Commit Graph

285 Commits

Author SHA1 Message Date
Steven Rostedt (Red Hat)
fcc742eaad ring-buffer: Add event descriptor to simplify passing data
Add rb_event_info descriptor to pass event info to functions a bit
easier than using a bunch of parameters. This will also allow for
changing the code around a bit to find better fast paths.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-07-20 22:30:46 -04:00
Steven Rostedt (Red Hat)
a497adb45b ring-buffer: Add enum names for the context levels
Instead of having hard coded numbers for the context levels, use
enums to describe them more.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-29 10:39:08 -04:00
Steven Rostedt (Red Hat)
3c6296f716 ring-buffer: Remove useless unused tracing_off_permanent()
The tracing_off_permanent() call is a way to disable all ring_buffers.
Nothing uses it and nothing should use it, as tracing_off() and
friends are better, as they disable the ring buffers related to
tracing. The tracing_off_permanent() even disabled non tracing
ring buffers. This is a bit drastic, and was added to handle NMIs
doing outputs that could corrupt the ring buffer when only tracing
used them. It is now obsolete and adds a little overhead, it should
be removed.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-28 16:47:39 -04:00
Steven Rostedt (Red Hat)
289a5a25c5 ring-buffer: Give NMIs a chance to lock the reader_lock
Currently, if an NMI does a dump of a ring buffer, it disables
all ring buffers from ever doing any writes again. This is because
it wont take the locks for the cpu_buffer and this can cause
corruption if it preempted a read, or a read happens on another
CPU for the current cpu buffer. This is a bit overkill.

First, it should at least try to take the lock, and if it fails
then disable it. Also, there's no need to disable all ring
buffers, even those that are unrelated to what is being read.
Only disable the per cpu ring buffer that is being read if
it can not get the lock for it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-28 16:47:01 -04:00
Steven Rostedt (Red Hat)
985e871b28 ring-buffer: Add trace_recursive checks to ring_buffer_write()
The ring_buffer_write() function isn't protected by the trace recursive
writes. Luckily, this function is not used as much and is unlikely
to ever recurse. But it should still have the protection, because
even a call to ring_buffer_lock_reserve() could cause ring buffer
corruption if called when ring_buffer_write() is being used.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-27 10:48:56 -04:00
Steven Rostedt (Red Hat)
6776221bfe ring-buffer: Allways do the trace_recursive checks
Currently the trace_recursive checks are only done if CONFIG_TRACING
is enabled. That was because there use to be a dependency with tracing
for the recursive checks (it used the task_struct trace recursive
variable). But now it uses its own variable and there is no dependency.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-27 10:44:43 -04:00
Steven Rostedt (Red Hat)
58a09ec6e3 ring-buffer: Move recursive check to per_cpu descriptor
Instead of using a global per_cpu variable to perform the recursive
checks into the ring buffer, use the already existing per_cpu descriptor
that is part of the ring buffer itself.

Not only does this simplify the code, it also allows for one ring buffer
to be used within the guts of the use of another ring buffer. For example
trace_printk() can now be used within the ring buffer to record changes
done by an instance into the main ring buffer. The recursion checks
will prevent the trace_printk() itself from causing recursive issues
with the main ring buffer (it is just ignored), but the recursive
checks wont prevent the trace_printk() from recording other ring buffers.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-27 10:42:36 -04:00
Steven Rostedt (Red Hat)
3205f8063b ring-buffer: Add unlikelys to make fast path the default
I was running the trace_event benchmark and noticed that the times
to record a trace_event was all over the place. I looked at the assembly
of the ring_buffer_lock_reserver() and saw this:

 <ring_buffer_lock_reserve>:
       31 c0                   xor    %eax,%eax
       48 83 3d 76 47 bd 00    cmpq   $0x1,0xbd4776(%rip)        # ffffffff81d10d60 <ring_buffer_flags>
       01
       55                      push   %rbp
       48 89 e5                mov    %rsp,%rbp
       75 1d                   jne    ffffffff8113c60d <ring_buffer_lock_reserve+0x2d>
       65 ff 05 69 e3 ec 7e    incl   %gs:0x7eece369(%rip)        # a960 <__preempt_count>
       8b 47 08                mov    0x8(%rdi),%eax
       85 c0                   test   %eax,%eax
 +---- 74 12                   je     ffffffff8113c610 <ring_buffer_lock_reserve+0x30>
 |     65 ff 0d 5b e3 ec 7e    decl   %gs:0x7eece35b(%rip)        # a960 <__preempt_count>
 |     0f 84 85 00 00 00       je     ffffffff8113c690 <ring_buffer_lock_reserve+0xb0>
 |     31 c0                   xor    %eax,%eax
 |     5d                      pop    %rbp
 |     c3                      retq
 |     90                      nop
 +---> 65 44 8b 05 48 e3 ec    mov    %gs:0x7eece348(%rip),%r8d        # a960 <__preempt_count>
       7e
       41 81 e0 ff ff ff 7f    and    $0x7fffffff,%r8d
       b0 08                   mov    $0x8,%al
       65 8b 0d 58 36 ed 7e    mov    %gs:0x7eed3658(%rip),%ecx        # fc80 <current_context>
       41 f7 c0 00 ff 1f 00    test   $0x1fff00,%r8d
       74 1e                   je     ffffffff8113c64f <ring_buffer_lock_reserve+0x6f>
       41 f7 c0 00 00 10 00    test   $0x100000,%r8d
       b0 01                   mov    $0x1,%al
       75 13                   jne    ffffffff8113c64f <ring_buffer_lock_reserve+0x6f>
       41 81 e0 00 00 0f 00    and    $0xf0000,%r8d
       49 83 f8 01             cmp    $0x1,%r8
       19 c0                   sbb    %eax,%eax
       83 e0 02                and    $0x2,%eax
       83 c0 02                add    $0x2,%eax
       85 c8                   test   %ecx,%eax
       75 ab                   jne    ffffffff8113c5fe <ring_buffer_lock_reserve+0x1e>
       09 c8                   or     %ecx,%eax
       65 89 05 24 36 ed 7e    mov    %eax,%gs:0x7eed3624(%rip)        # fc80 <current_context>

The arrow is the fast path.

After adding the unlikely's, the fast path looks a bit better:

 <ring_buffer_lock_reserve>:
       31 c0                   xor    %eax,%eax
       48 83 3d 76 47 bd 00    cmpq   $0x1,0xbd4776(%rip)        # ffffffff81d10d60 <ring_buffer_flags>
       01
       55                      push   %rbp
       48 89 e5                mov    %rsp,%rbp
       75 7b                   jne    ffffffff8113c66b <ring_buffer_lock_reserve+0x8b>
       65 ff 05 69 e3 ec 7e    incl   %gs:0x7eece369(%rip)        # a960 <__preempt_count>
       8b 47 08                mov    0x8(%rdi),%eax
       85 c0                   test   %eax,%eax
       0f 85 9f 00 00 00       jne    ffffffff8113c6a1 <ring_buffer_lock_reserve+0xc1>
       65 8b 0d 57 e3 ec 7e    mov    %gs:0x7eece357(%rip),%ecx        # a960 <__preempt_count>
       81 e1 ff ff ff 7f       and    $0x7fffffff,%ecx
       b0 08                   mov    $0x8,%al
       65 8b 15 68 36 ed 7e    mov    %gs:0x7eed3668(%rip),%edx        # fc80 <current_context>
       f7 c1 00 ff 1f 00       test   $0x1fff00,%ecx
       75 50                   jne    ffffffff8113c670 <ring_buffer_lock_reserve+0x90>
       85 d0                   test   %edx,%eax
       75 7d                   jne    ffffffff8113c6a1 <ring_buffer_lock_reserve+0xc1>
       09 d0                   or     %edx,%eax
       65 89 05 53 36 ed 7e    mov    %eax,%gs:0x7eed3653(%rip)        # fc80 <current_context>
       65 8b 05 fc da ec 7e    mov    %gs:0x7eecdafc(%rip),%eax        # a130 <cpu_number>
       89 c2                   mov    %eax,%edx

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-21 17:39:29 -04:00
Steven Rostedt (Red Hat)
af658dca22 tracing: Rename ftrace_event.h to trace_events.h
The term "ftrace" is really the infrastructure of the function hooks,
and not the trace events. Rename ftrace_event.h to trace_events.h to
represent the trace_event infrastructure and decouple the term ftrace
from it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-05-13 14:05:12 -04:00
Steven Rostedt (Red Hat)
d631c8cceb ring-buffer: Remove duplicate use of '&' in recursive code
A clean up of the recursive protection code changed

  val = this_cpu_read(current_context);
  val--;
  val &= this_cpu_read(current_context);

to

  val = this_cpu_read(current_context);
  val &= val & (val - 1);

Which has a duplicate use of '&' as the above is the same as

  val = val & (val - 1);

Actually, it would be best to remove that line altogether and
just add it to where it is used.

And Christoph even mentioned that it can be further compacted to
just a single line:

  __this_cpu_and(current_context, __this_cpu_read(current_context) - 1);

Link: http://lkml.kernel.org/alpine.DEB.2.11.1503271423580.23114@gentwo.org

Suggested-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-03-30 13:36:31 -04:00
Steven Rostedt
80a9b64e2c ring-buffer: Replace this_cpu_*() with __this_cpu_*()
It has come to my attention that this_cpu_read/write are horrible on
architectures other than x86. Worse yet, they actually disable
preemption or interrupts! This caused some unexpected tracing results
on ARM.

   101.356868: preempt_count_add <-ring_buffer_lock_reserve
   101.356870: preempt_count_sub <-ring_buffer_lock_reserve

The ring_buffer_lock_reserve has recursion protection that requires
accessing a per cpu variable. But since preempt_disable() is traced, it
too got traced while accessing the variable that is suppose to prevent
recursion like this.

The generic version of this_cpu_read() and write() are:

 #define this_cpu_generic_read(pcp)					\
 ({	typeof(pcp) ret__;						\
	preempt_disable();						\
	ret__ = *this_cpu_ptr(&(pcp));					\
	preempt_enable();						\
	ret__;								\
 })

 #define this_cpu_generic_to_op(pcp, val, op)				\
 do {									\
	unsigned long flags;						\
	raw_local_irq_save(flags);					\
	*__this_cpu_ptr(&(pcp)) op val;					\
	raw_local_irq_restore(flags);					\
 } while (0)

Which is unacceptable for locations that know they are within preempt
disabled or interrupt disabled locations.

Paul McKenney stated that __this_cpu_() versions produce much better code on
other architectures than this_cpu_() does, if we know that the call is done in
a preempt disabled location.

I also changed the recursive_unlock() to use two local variables instead
of accessing the per_cpu variable twice.

Link: http://lkml.kernel.org/r/20150317114411.GE3589@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20150317104038.312e73d1@gandalf.local.home

Cc: stable@vger.kernel.org
Acked-by: Christoph Lameter <cl@linux.com>
Reported-by: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Tested-by: Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-03-25 08:56:49 -04:00
Steven Rostedt (Red Hat)
1e0d6714ac ring-buffer: Do not wake up a splice waiter when page is not full
When an application connects to the ring buffer via splice, it can only
read full pages. Splice does not work with partial pages. If there is
not enough data to fill a page, the splice command will either block
or return -EAGAIN (if set to nonblock).

Code was added where if the page is not full, to just sleep again.
The problem is, it will get woken up again on the next event. That
is, when something is written into the ring buffer, if there is a waiter
it will wake it up. The waiter would then check the buffer, see that
it still does not have enough data to fill a page and go back to sleep.
To make matters worse, when the waiter goes back to sleep, it could
cause another event, which would wake it back up again to see it
doesn't have enough data and sleep again. This produces a tremendous
overhead and fills the ring buffer with noise.

For example, recording sched_switch on an idle system for 10 seconds
produces 25,350,475 events!!!

Create another wait queue for those waiters wanting full pages.
When an event is written, it only wakes up waiters if there's a full
page of data. It does not wake up the waiter if the page is not yet
full.

After this change, recording sched_switch on an idle system for 10
seconds produces only 800 events. Getting rid of 25,349,675 useless
events (99.9969% of events!!), is something to take seriously.

Cc: stable@vger.kernel.org # 3.16+
Cc: Rabin Vincent <rabin@rab.in>
Fixes: e30f53aad2 "tracing: Do not busy wait in buffer splice"
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-02-11 07:41:42 -05:00
Steven Rostedt (Red Hat)
3efb5f21a3 tracing: Remove unneeded includes of debugfs.h and fs.h
The creation of tracing files and directories is for the most part
encapsulated in helper functions in trace.c. Other files do not need to
include debugfs.h or fs.h, as they may have needed to in the past.

Remove them from the files that do not need them.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-01-22 11:19:48 -05:00
Linus Torvalds
1dd7dcb6ea There was a lot of clean ups and minor fixes. One of those clean ups was
to the trace_seq code. It also removed the return values to the
 trace_seq_*() functions and use trace_seq_has_overflowed() to see if
 the buffer filled up or not. This is similar to work being done to the
 seq_file code as well in another tree.
 
 Some of the other goodies include:
 
  o Added some "!" (NOT) logic to the tracing filter.
 
  o Fixed the frame pointer logic to the x86_64 mcount trampolines
 
  o Added the logic for dynamic trampolines on !CONFIG_PREEMPT systems.
    That is, the ftrace trampoline can be dynamically allocated
    and be called directly by functions that only have a single hook
    to them.
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Merge tag 'trace-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "There was a lot of clean ups and minor fixes.  One of those clean ups
  was to the trace_seq code.  It also removed the return values to the
  trace_seq_*() functions and use trace_seq_has_overflowed() to see if
  the buffer filled up or not.  This is similar to work being done to
  the seq_file code as well in another tree.

  Some of the other goodies include:

   - Added some "!" (NOT) logic to the tracing filter.

   - Fixed the frame pointer logic to the x86_64 mcount trampolines

   - Added the logic for dynamic trampolines on !CONFIG_PREEMPT systems.
     That is, the ftrace trampoline can be dynamically allocated and be
     called directly by functions that only have a single hook to them"

* tag 'trace-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (55 commits)
  tracing: Truncated output is better than nothing
  tracing: Add additional marks to signal very large time deltas
  Documentation: describe trace_buf_size parameter more accurately
  tracing: Allow NOT to filter AND and OR clauses
  tracing: Add NOT to filtering logic
  ftrace/fgraph/x86: Have prepare_ftrace_return() take ip as first parameter
  ftrace/x86: Get rid of ftrace_caller_setup
  ftrace/x86: Have save_mcount_regs macro also save stack frames if needed
  ftrace/x86: Add macro MCOUNT_REG_SIZE for amount of stack used to save mcount regs
  ftrace/x86: Simplify save_mcount_regs on getting RIP
  ftrace/x86: Have save_mcount_regs store RIP in %rdi for first parameter
  ftrace/x86: Rename MCOUNT_SAVE_FRAME and add more detailed comments
  ftrace/x86: Move MCOUNT_SAVE_FRAME out of header file
  ftrace/x86: Have static tracing also use ftrace_caller_setup
  ftrace/x86: Have static function tracing always test for function graph
  kprobes: Add IPMODIFY flag to kprobe_ftrace_ops
  ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict
  kprobes/ftrace: Recover original IP if pre_handler doesn't change it
  tracing/trivial: Fix typos and make an int into a bool
  tracing: Deletion of an unnecessary check before iput()
  ...
2014-12-10 19:58:13 -08:00
Steven Rostedt (Red Hat)
c0cd93aa16 ring-buffer: Remove check of trace_seq_{puts,printf}() return values
Remove checking the return value of all trace_seq_puts(). It was wrong
anyway as only the last return value mattered. But as the trace_seq_puts()
is going to be a void function in the future, we should not be checking
the return value of it anyway.

Just return !trace_seq_has_overflowed() instead.

Reviewed-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-11-19 15:25:40 -05:00
Rabin Vincent
e30f53aad2 tracing: Do not busy wait in buffer splice
On a !PREEMPT kernel, attempting to use trace-cmd results in a soft
lockup:

 # trace-cmd record -e raw_syscalls:* -F false
 NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [trace-cmd:61]
 ...
 Call Trace:
  [<ffffffff8105b580>] ? __wake_up_common+0x90/0x90
  [<ffffffff81092e25>] wait_on_pipe+0x35/0x40
  [<ffffffff810936e3>] tracing_buffers_splice_read+0x2e3/0x3c0
  [<ffffffff81093300>] ? tracing_stats_read+0x2a0/0x2a0
  [<ffffffff812d10ab>] ? _raw_spin_unlock+0x2b/0x40
  [<ffffffff810dc87b>] ? do_read_fault+0x21b/0x290
  [<ffffffff810de56a>] ? handle_mm_fault+0x2ba/0xbd0
  [<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
  [<ffffffff810951e2>] ? trace_buffer_lock_reserve+0x22/0x60
  [<ffffffff81095c80>] ? trace_event_buffer_lock_reserve+0x40/0x80
  [<ffffffff8112415d>] do_splice_to+0x6d/0x90
  [<ffffffff81126971>] SyS_splice+0x7c1/0x800
  [<ffffffff812d1edd>] tracesys_phase2+0xd3/0xd8

The problem is this: tracing_buffers_splice_read() calls
ring_buffer_wait() to wait for data in the ring buffers.  The buffers
are not empty so ring_buffer_wait() returns immediately.  But
tracing_buffers_splice_read() calls ring_buffer_read_page() with full=1,
meaning it only wants to read a full page.  When the full page is not
available, tracing_buffers_splice_read() tries to wait again with
ring_buffer_wait(), which again returns immediately, and so on.

Fix this by adding a "full" argument to ring_buffer_wait() which will
make ring_buffer_wait() wait until the writer has left the reader's
page, i.e.  until full-page reads will succeed.

Link: http://lkml.kernel.org/r/1415645194-25379-1-git-send-email-rabin@rab.in

Cc: stable@vger.kernel.org # 3.16+
Fixes: b1169cc69b ("tracing: Remove mock up poll wait function")
Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-11-10 16:45:43 -05:00
Steven Rostedt (Red Hat)
24607f114f ring-buffer: Fix infinite spin in reading buffer
Commit 651e22f270 "ring-buffer: Always reset iterator to reader page"
fixed one bug but in the process caused another one. The reset is to
update the header page, but that fix also changed the way the cached
reads were updated. The cache reads are used to test if an iterator
needs to be updated or not.

A ring buffer iterator, when created, disables writes to the ring buffer
but does not stop other readers or consuming reads from happening.
Although all readers are synchronized via a lock, they are only
synchronized when in the ring buffer functions. Those functions may
be called by any number of readers. The iterator continues down when
its not interrupted by a consuming reader. If a consuming read
occurs, the iterator starts from the beginning of the buffer.

The way the iterator sees that a consuming read has happened since
its last read is by checking the reader "cache". The cache holds the
last counts of the read and the reader page itself.

Commit 651e22f270 changed what was saved by the cache_read when
the rb_iter_reset() occurred, making the iterator never match the cache.
Then if the iterator calls rb_iter_reset(), it will go into an
infinite loop by checking if the cache doesn't match, doing the reset
and retrying, just to see that the cache still doesn't match! Which
should never happen as the reset is suppose to set the cache to the
current value and there's locks that keep a consuming reader from
having access to the data.

Fixes: 651e22f270 "ring-buffer: Always reset iterator to reader page"
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-10-02 16:51:18 -04:00
Josef Bacik
4ce97dbf50 trace: Fix epoll hang when we race with new entries
Epoll on trace_pipe can sometimes hang in a weird case.  If the ring buffer is
empty when we set waiters_pending but an event shows up exactly at that moment
we can miss being woken up by the ring buffers irq work.  Since
ring_buffer_empty() is inherently racey we will sometimes think that the buffer
is not empty.  So we don't get woken up and we don't think there are any events
even though there were some ready when we added the watch, which makes us hang.
This patch fixes this by making sure that we are actually on the wait list
before we set waiters_pending, and add a memory barrier to make sure
ring_buffer_empty() is going to be correct.

Link: http://lkml.kernel.org/p/1408989581-23727-1-git-send-email-jbacik@fb.com

Cc: stable@vger.kernel.org # 3.10+
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-08-25 20:18:11 -04:00
Linus Torvalds
fc335c1b68 This contains a fix for two long standing bugs. Both of which are
rarely ever hit, and requires the user to do something that users rarely
 do. It took a few special test cases to even trigger this bug,
 and one of them was just one test in the process of finishing up as another
 one started.
 
 Both bugs have to do with the ring buffer iterator rb_iter_peek(), but one
 is more indirect than the other.
 
 The fist bug fix is simply an increase in the safety net loop counter.
 The counter makes sure that the rb_iter_peek() only iterates the number
 of times we expect it can, and no more. Well, there was one way it could
 iterate one more than we expected, and that caused the ring buffer
 to shutdown with a nasty warning. The fix was simply to up that counter by
 one.
 
 The other bug has to be with rb_iter_reset() (called by rb_iter_peek()).
 This happens when a user reads both the trace_pipe and trace files.
 The trace_pipe is a consuming read and does not use the ring buffer
 iterator, but the trace file is not a consuming read and does use the
 ring buffer iterator. When the trace file is being read, if it detects
 that a consuming read occurred, it resets the iterator and starts over.
 But the reset code that does this (rb_iter_reset()), checks if the
 reader_page is linked to the ring buffer or not, and will look into
 the ring buffer itself if it is not. This is wrong, as it should always
 try to read the reader page first. Not to mention, the code that looked
 into the ring buffer did it wrong, and used the header_page "read" offset
 to start reading on that page. That offset is bogus for pages in the
 writable ring buffer, and was corrupting the iterator, and it would start
 returning bogus events.
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Merge tag 'trace-fixes-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull trace file read iterator fixes from Steven Rostedt:
 "This contains a fix for two long standing bugs.  Both of which are
  rarely ever hit, and requires the user to do something that users
  rarely do.  It took a few special test cases to even trigger this bug,
  and one of them was just one test in the process of finishing up as
  another one started.

  Both bugs have to do with the ring buffer iterator rb_iter_peek(), but
  one is more indirect than the other.

  The fist bug fix is simply an increase in the safety net loop counter.
  The counter makes sure that the rb_iter_peek() only iterates the
  number of times we expect it can, and no more.  Well, there was one
  way it could iterate one more than we expected, and that caused the
  ring buffer to shutdown with a nasty warning.  The fix was simply to
  up that counter by one.

  The other bug has to be with rb_iter_reset() (called by
  rb_iter_peek()).  This happens when a user reads both the trace_pipe
  and trace files.  The trace_pipe is a consuming read and does not use
  the ring buffer iterator, but the trace file is not a consuming read
  and does use the ring buffer iterator.  When the trace file is being
  read, if it detects that a consuming read occurred, it resets the
  iterator and starts over.  But the reset code that does this
  (rb_iter_reset()), checks if the reader_page is linked to the ring
  buffer or not, and will look into the ring buffer itself if it is not.
  This is wrong, as it should always try to read the reader page first.
  Not to mention, the code that looked into the ring buffer did it
  wrong, and used the header_page "read" offset to start reading on that
  page.  That offset is bogus for pages in the writable ring buffer, and
  was corrupting the iterator, and it would start returning bogus
  events"

* tag 'trace-fixes-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ring-buffer: Always reset iterator to reader page
  ring-buffer: Up rb_iter_peek() loop count to 3
2014-08-09 17:29:36 -07:00
Steven Rostedt (Red Hat)
651e22f270 ring-buffer: Always reset iterator to reader page
When performing a consuming read, the ring buffer swaps out a
page from the ring buffer with a empty page and this page that
was swapped out becomes the new reader page. The reader page
is owned by the reader and since it was swapped out of the ring
buffer, writers do not have access to it (there's an exception
to that rule, but it's out of scope for this commit).

When reading the "trace" file, it is a non consuming read, which
means that the data in the ring buffer will not be modified.
When the trace file is opened, a ring buffer iterator is allocated
and writes to the ring buffer are disabled, such that the iterator
will not have issues iterating over the data.

Although the ring buffer disabled writes, it does not disable other
reads, or even consuming reads. If a consuming read happens, then
the iterator is reset and starts reading from the beginning again.

My tests would sometimes trigger this bug on my i386 box:

WARNING: CPU: 0 PID: 5175 at kernel/trace/trace.c:1527 __trace_find_cmdline+0x66/0xaa()
Modules linked in:
CPU: 0 PID: 5175 Comm: grep Not tainted 3.16.0-rc3-test+ #8
Hardware name:                  /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006
 00000000 00000000 f09c9e1c c18796b3 c1b5d74c f09c9e4c c103a0e3 c1b5154b
 f09c9e78 00001437 c1b5d74c 000005f7 c10bd85a c10bd85a c1cac57c f09c9eb0
 ed0e0000 f09c9e64 c103a185 00000009 f09c9e5c c1b5154b f09c9e78 f09c9e80^M
Call Trace:
 [<c18796b3>] dump_stack+0x4b/0x75
 [<c103a0e3>] warn_slowpath_common+0x7e/0x95
 [<c10bd85a>] ? __trace_find_cmdline+0x66/0xaa
 [<c10bd85a>] ? __trace_find_cmdline+0x66/0xaa
 [<c103a185>] warn_slowpath_fmt+0x33/0x35
 [<c10bd85a>] __trace_find_cmdline+0x66/0xaa^M
 [<c10bed04>] trace_find_cmdline+0x40/0x64
 [<c10c3c16>] trace_print_context+0x27/0xec
 [<c10c4360>] ? trace_seq_printf+0x37/0x5b
 [<c10c0b15>] print_trace_line+0x319/0x39b
 [<c10ba3fb>] ? ring_buffer_read+0x47/0x50
 [<c10c13b1>] s_show+0x192/0x1ab
 [<c10bfd9a>] ? s_next+0x5a/0x7c
 [<c112e76e>] seq_read+0x267/0x34c
 [<c1115a25>] vfs_read+0x8c/0xef
 [<c112e507>] ? seq_lseek+0x154/0x154
 [<c1115ba2>] SyS_read+0x54/0x7f
 [<c188488e>] syscall_call+0x7/0xb
---[ end trace 3f507febd6b4cc83 ]---
>>>> ##### CPU 1 buffer started ####

Which was the __trace_find_cmdline() function complaining about the pid
in the event record being negative.

After adding more test cases, this would trigger more often. Strangely
enough, it would never trigger on a single test, but instead would trigger
only when running all the tests. I believe that was the case because it
required one of the tests to be shutting down via delayed instances while
a new test started up.

After spending several days debugging this, I found that it was caused by
the iterator becoming corrupted. Debugging further, I found out why
the iterator became corrupted. It happened with the rb_iter_reset().

As consuming reads may not read the full reader page, and only part
of it, there's a "read" field to know where the last read took place.
The iterator, must also start at the read position. In the rb_iter_reset()
code, if the reader page was disconnected from the ring buffer, the iterator
would start at the head page within the ring buffer (where writes still
happen). But the mistake there was that it still used the "read" field
to start the iterator on the head page, where it should always start
at zero because readers never read from within the ring buffer where
writes occur.

I originally wrote a patch to have it set the iter->head to 0 instead
of iter->head_page->read, but then I questioned why it wasn't always
setting the iter to point to the reader page, as the reader page is
still valid.  The list_empty(reader_page->list) just means that it was
successful in swapping out. But the reader_page may still have data.

There was a bug report a long time ago that was not reproducible that
had something about trace_pipe (consuming read) not matching trace
(iterator read). This may explain why that happened.

Anyway, the correct answer to this bug is to always use the reader page
an not reset the iterator to inside the writable ring buffer.

Cc: stable@vger.kernel.org # 2.6.28+
Fixes: d769041f86 "ring_buffer: implement new locking"
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-08-06 16:06:34 -04:00
Steven Rostedt (Red Hat)
021de3d904 ring-buffer: Up rb_iter_peek() loop count to 3
After writting a test to try to trigger the bug that caused the
ring buffer iterator to become corrupted, I hit another bug:

 WARNING: CPU: 1 PID: 5281 at kernel/trace/ring_buffer.c:3766 rb_iter_peek+0x113/0x238()
 Modules linked in: ipt_MASQUERADE sunrpc [...]
 CPU: 1 PID: 5281 Comm: grep Tainted: G        W     3.16.0-rc3-test+ #143
 Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
  0000000000000000 ffffffff81809a80 ffffffff81503fb0 0000000000000000
  ffffffff81040ca1 ffff8800796d6010 ffffffff810c138d ffff8800796d6010
  ffff880077438c80 ffff8800796d6010 ffff88007abbe600 0000000000000003
 Call Trace:
  [<ffffffff81503fb0>] ? dump_stack+0x4a/0x75
  [<ffffffff81040ca1>] ? warn_slowpath_common+0x7e/0x97
  [<ffffffff810c138d>] ? rb_iter_peek+0x113/0x238
  [<ffffffff810c138d>] ? rb_iter_peek+0x113/0x238
  [<ffffffff810c14df>] ? ring_buffer_iter_peek+0x2d/0x5c
  [<ffffffff810c6f73>] ? tracing_iter_reset+0x6e/0x96
  [<ffffffff810c74a3>] ? s_start+0xd7/0x17b
  [<ffffffff8112b13e>] ? kmem_cache_alloc_trace+0xda/0xea
  [<ffffffff8114cf94>] ? seq_read+0x148/0x361
  [<ffffffff81132d98>] ? vfs_read+0x93/0xf1
  [<ffffffff81132f1b>] ? SyS_read+0x60/0x8e
  [<ffffffff8150bf9f>] ? tracesys+0xdd/0xe2

Debugging this bug, which triggers when the rb_iter_peek() loops too
many times (more than 2 times), I discovered there's a case that can
cause that function to legitimately loop 3 times!

rb_iter_peek() is different than rb_buffer_peek() as the rb_buffer_peek()
only deals with the reader page (it's for consuming reads). The
rb_iter_peek() is for traversing the buffer without consuming it, and as
such, it can loop for one more reason. That is, if we hit the end of
the reader page or any page, it will go to the next page and try again.

That is, we have this:

 1. iter->head > iter->head_page->page->commit
    (rb_inc_iter() which moves the iter to the next page)
    try again

 2. event = rb_iter_head_event()
    event->type_len == RINGBUF_TYPE_TIME_EXTEND
    rb_advance_iter()
    try again

 3. read the event.

But we never get to 3, because the count is greater than 2 and we
cause the WARNING and return NULL.

Up the counter to 3.

Cc: stable@vger.kernel.org # 2.6.37+
Fixes: 69d1b839f7 "ring-buffer: Bind time extend and data events together"
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-08-06 16:06:33 -04:00
Linus Torvalds
b8c0aa46b3 This pull request has a lot of work done. The main thing is the changes
to the ftrace function callback infrastructure. It's introducing a
 way to allow different functions to call directly different trampolines
 instead of all calling the same "mcount" one.
 
 The only user of this for now is the function graph tracer, which always
 had a different trampoline, but the function tracer trampoline was called
 and did basically nothing, and then the function graph tracer trampoline
 was called. The difference now, is that the function graph tracer
 trampoline can be called directly if a function is only being traced by
 the function graph trampoline. If function tracing is also happening on
 the same function, the old way is still done.
 
 The accounting for this takes up more memory when function graph tracing
 is activated, as it needs to keep track of which functions it uses.
 I have a new way that wont take as much memory, but it's not ready yet
 for this merge window, and will have to wait for the next one.
 
 Another big change was the removal of the ftrace_start/stop() calls that
 were used by the suspend/resume code that stopped function tracing when
 entering into suspend and resume paths. The stop of ftrace was done
 because there was some function that would crash the system if one called
 smp_processor_id()! The stop/start was a big hammer to solve the issue
 at the time, which was when ftrace was first introduced into Linux.
 Now ftrace has better infrastructure to debug such issues, and I found
 the problem function and labeled it with "notrace" and function tracing
 can now safely be activated all the way down into the guts of suspend
 and resume.
 
 Other changes include clean ups of uprobe code.
 Clean up of the trace_seq() code.
 And other various small fixes and clean ups to ftrace and tracing.
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Merge tag 'trace-3.17' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "This pull request has a lot of work done.  The main thing is the
  changes to the ftrace function callback infrastructure.  It's
  introducing a way to allow different functions to call directly
  different trampolines instead of all calling the same "mcount" one.

  The only user of this for now is the function graph tracer, which
  always had a different trampoline, but the function tracer trampoline
  was called and did basically nothing, and then the function graph
  tracer trampoline was called.  The difference now, is that the
  function graph tracer trampoline can be called directly if a function
  is only being traced by the function graph trampoline.  If function
  tracing is also happening on the same function, the old way is still
  done.

  The accounting for this takes up more memory when function graph
  tracing is activated, as it needs to keep track of which functions it
  uses.  I have a new way that wont take as much memory, but it's not
  ready yet for this merge window, and will have to wait for the next
  one.

  Another big change was the removal of the ftrace_start/stop() calls
  that were used by the suspend/resume code that stopped function
  tracing when entering into suspend and resume paths.  The stop of
  ftrace was done because there was some function that would crash the
  system if one called smp_processor_id()! The stop/start was a big
  hammer to solve the issue at the time, which was when ftrace was first
  introduced into Linux.  Now ftrace has better infrastructure to debug
  such issues, and I found the problem function and labeled it with
  "notrace" and function tracing can now safely be activated all the way
  down into the guts of suspend and resume

  Other changes include clean ups of uprobe code, clean up of the
  trace_seq() code, and other various small fixes and clean ups to
  ftrace and tracing"

* tag 'trace-3.17' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (57 commits)
  ftrace: Add warning if tramp hash does not match nr_trampolines
  ftrace: Fix trampoline hash update check on rec->flags
  ring-buffer: Use rb_page_size() instead of open coded head_page size
  ftrace: Rename ftrace_ops field from trampolines to nr_trampolines
  tracing: Convert local function_graph functions to static
  ftrace: Do not copy old hash when resetting
  tracing: let user specify tracing_thresh after selecting function_graph
  ring-buffer: Always run per-cpu ring buffer resize with schedule_work_on()
  tracing: Remove function_trace_stop and HAVE_FUNCTION_TRACE_MCOUNT_TEST
  s390/ftrace: remove check of obsolete variable function_trace_stop
  arm64, ftrace: Remove check of obsolete variable function_trace_stop
  Blackfin: ftrace: Remove check of obsolete variable function_trace_stop
  metag: ftrace: Remove check of obsolete variable function_trace_stop
  microblaze: ftrace: Remove check of obsolete variable function_trace_stop
  MIPS: ftrace: Remove check of obsolete variable function_trace_stop
  parisc: ftrace: Remove check of obsolete variable function_trace_stop
  sh: ftrace: Remove check of obsolete variable function_trace_stop
  sparc64,ftrace: Remove check of obsolete variable function_trace_stop
  tile: ftrace: Remove check of obsolete variable function_trace_stop
  ftrace: x86: Remove check of obsolete variable function_trace_stop
  ...
2014-08-04 11:50:00 -07:00
Steven Rostedt (Red Hat)
10e83fd01c ring-buffer: Use rb_page_size() instead of open coded head_page size
There's a helper function to get a ring buffer page size (the number
of bytes of data recorded on the page), called rb_page_size().
Use that instead of open coding it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-07-23 19:45:12 -04:00
Corey Minyard
021c5b3445 ring-buffer: Always run per-cpu ring buffer resize with schedule_work_on()
The code for resizing the trace ring buffers has to run the per-cpu
resize on the CPU itself.  The code was using preempt_off() and
running the code for the current CPU directly, otherwise calling
schedule_work_on().

At least on RT this could result in the following:

|BUG: sleeping function called from invalid context at kernel/rtmutex.c:673
|in_atomic(): 1, irqs_disabled(): 0, pid: 607, name: bash
|3 locks held by bash/607:
|CPU: 0 PID: 607 Comm: bash Not tainted 3.12.15-rt25+ #124
|(rt_spin_lock+0x28/0x68)
|(free_hot_cold_page+0x84/0x3b8)
|(free_buffer_page+0x14/0x20)
|(rb_update_pages+0x280/0x338)
|(ring_buffer_resize+0x32c/0x3dc)
|(free_snapshot+0x18/0x38)
|(tracing_set_tracer+0x27c/0x2ac)

probably via
|cd /sys/kernel/debug/tracing/
|echo 1 > events/enable ; sleep 2
|echo 1024 > buffer_size_kb

If we just always use schedule_work_on(), there's no need for the
preempt_off().  So do that.

Link: http://lkml.kernel.org/p/1405537633-31518-1-git-send-email-cminyard@mvista.com

Reported-by: Stanislav Meduna <stano@meduna.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-07-18 13:58:12 -04:00
Martin Lau
97b8ee8453 ring-buffer: Fix polling on trace_pipe
ring_buffer_poll_wait() should always put the poll_table to its wait_queue
even there is immediate data available.  Otherwise, the following epoll and
read sequence will eventually hang forever:

1. Put some data to make the trace_pipe ring_buffer read ready first
2. epoll_ctl(efd, EPOLL_CTL_ADD, trace_pipe_fd, ee)
3. epoll_wait()
4. read(trace_pipe_fd) till EAGAIN
5. Add some more data to the trace_pipe ring_buffer
6. epoll_wait() -> this epoll_wait() will block forever

~ During the epoll_ctl(efd, EPOLL_CTL_ADD,...) call in step 2,
  ring_buffer_poll_wait() returns immediately without adding poll_table,
  which has poll_table->_qproc pointing to ep_poll_callback(), to its
  wait_queue.
~ During the epoll_wait() call in step 3 and step 6,
  ring_buffer_poll_wait() cannot add ep_poll_callback() to its wait_queue
  because the poll_table->_qproc is NULL and it is how epoll works.
~ When there is new data available in step 6, ring_buffer does not know
  it has to call ep_poll_callback() because it is not in its wait queue.
  Hence, block forever.

Other poll implementation seems to call poll_wait() unconditionally as the very
first thing to do.  For example, tcp_poll() in tcp.c.

Link: http://lkml.kernel.org/p/20140610060637.GA14045@devbig242.prn2.facebook.com

Cc: stable@vger.kernel.org # 2.6.27
Fixes: 2a2cc8f7c4 "ftrace: allow the event pipe to be polled"
Reviewed-by: Chris Mason <clm@fb.com>
Signed-off-by: Martin Lau <kafai@fb.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-07-15 17:07:47 -04:00
Steven Rostedt (Red Hat)
8b8b36834d ring-buffer: Check if buffer exists before polling
The per_cpu buffers are created one per possible CPU. But these do
not mean that those CPUs are online, nor do they even exist.

With the addition of the ring buffer polling, it assumes that the
caller polls on an existing buffer. But this is not the case if
the user reads trace_pipe from a CPU that does not exist, and this
causes the kernel to crash.

Simple fix is to check the cpu against buffer bitmask against to see
if the buffer was allocated or not and return -ENODEV if it is
not.

More updates were done to pass the -ENODEV back up to userspace.

Link: http://lkml.kernel.org/r/5393DB61.6060707@oracle.com

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-06-10 09:46:00 -04:00
Srivatsa S. Bhat
d39ad278a3 trace, ring-buffer: Fix CPU hotplug callback registration
Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the tracing ring-buffer code by using this latter form of callback
registration.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-03-20 13:43:48 +01:00
Steven Rostedt (Red Hat)
d651aa1d68 ring-buffer: Fix first commit on sub-buffer having non-zero delta
Each sub-buffer (buffer page) has a full 64 bit timestamp. The events on
that page use a 27 bit delta against that timestamp in order to save on
bits written to the ring buffer. If the time between events is larger than
what the 27 bits can hold, a "time extend" event is added to hold the
entire 64 bit timestamp again and the events after that hold a delta from
that timestamp.

As a "time extend" is always paired with an event, it is logical to just
allocate the event with the time extend, to make things a bit more efficient.

Unfortunately, when the pairing code was written, it removed the "delta = 0"
from the first commit on a page, causing the events on the page to be
slightly skewed.

Fixes: 69d1b839f7 "ring-buffer: Bind time extend and data events together"
Cc: stable@vger.kernel.org # 2.6.37+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-02-11 13:38:54 -05:00
Peter Zijlstra
35af99e646 sched/clock, x86: Use a static_key for sched_clock_stable
In order to avoid the runtime condition and variable load turn
sched_clock_stable into a static_key.

Also provide a shorter implementation of local_clock() and
cpu_clock(int) when sched_clock_stable==1.

                        MAINLINE   PRE       POST

    sched_clock_stable: 1          1         1
    (cold) sched_clock: 329841     221876    215295
    (cold) local_clock: 301773     234692    220773
    (warm) sched_clock: 38375      25602     25659
    (warm) local_clock: 100371     33265     27242
    (warm) rdtsc:       27340      24214     24208
    sched_clock_stable: 0          0         0
    (cold) sched_clock: 382634     235941    237019
    (cold) local_clock: 396890     297017    294819
    (warm) sched_clock: 38194      25233     25609
    (warm) local_clock: 143452     71234     71232
    (warm) rdtsc:       27345      24245     24243

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-eummbdechzz37mwmpags1gjr@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-01-13 15:13:13 +01:00
zhangwei(Jovi)
d611851b42 tracing: Typo fix on ring buffer comments
There have some mismatch between comments with
real function name, update it.

This patch also add some missed function arguments
description.

Link: http://lkml.kernel.org/r/51E3B3B2.4080307@huawei.com

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-18 21:31:26 -04:00
zhangwei(Jovi)
146c3442f2 tracing: Use trace_seq_puts()/trace_seq_putc() where possible
For string without format specifiers, use trace_seq_puts()
or trace_seq_putc().

Link: http://lkml.kernel.org/r/51E3B3AC.1000605@huawei.com

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
[ fixed a trace_seq_putc(s, " ") to trace_seq_putc(s, ' ') ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-07-18 21:30:36 -04:00
Steven Rostedt (Red Hat)
6721cb6002 ring-buffer: Do not poll non allocated cpu buffers
The tracing infrastructure sets up for possible CPUs, but it uses
the ring buffer polling, it is possible to call the ring buffer
polling code with a CPU that hasn't been allocated. This will cause
a kernel oops when it access a ring buffer cpu buffer that is part
of the possible cpus but hasn't been allocated yet as the CPU has never
been online.

Reported-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-05-28 10:53:20 -04:00
Linus Torvalds
9e8529afc4 Tracing updates for Linux 3.10
Along with the usual minor fixes and clean ups there are a few major
 changes with this pull request.
 
 1) Multiple buffers for the ftrace facility
 
 This feature has been requested by many people over the last few years.
 I even heard that Google was about to implement it themselves. I finally
 had time and cleaned up the code such that you can now create multiple
 instances of the ftrace buffer and have different events go to different
 buffers. This way, a low frequency event will not be lost in the noise
 of a high frequency event.
 
 Note, currently only events can go to different buffers, the tracers
 (ie. function, function_graph and the latency tracers) still can only
 be written to the main buffer.
 
 2) The function tracer triggers have now been extended.
 
 The function tracer had two triggers. One to enable tracing when a
 function is hit, and one to disable tracing. Now you can record a
 stack trace on a single (or many) function(s), take a snapshot of the
 buffer (copy it to the snapshot buffer), and you can enable or disable
 an event to be traced when a function is hit.
 
 3) A perf clock has been added.
 
 A "perf" clock can be chosen to be used when tracing. This will cause
 ftrace to use the same clock as perf uses, and hopefully this will make
 it easier to interleave the perf and ftrace data for analysis.
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Merge tag 'trace-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "Along with the usual minor fixes and clean ups there are a few major
  changes with this pull request.

   1) Multiple buffers for the ftrace facility

  This feature has been requested by many people over the last few
  years.  I even heard that Google was about to implement it themselves.
  I finally had time and cleaned up the code such that you can now
  create multiple instances of the ftrace buffer and have different
  events go to different buffers.  This way, a low frequency event will
  not be lost in the noise of a high frequency event.

  Note, currently only events can go to different buffers, the tracers
  (ie function, function_graph and the latency tracers) still can only
  be written to the main buffer.

   2) The function tracer triggers have now been extended.

  The function tracer had two triggers.  One to enable tracing when a
  function is hit, and one to disable tracing.  Now you can record a
  stack trace on a single (or many) function(s), take a snapshot of the
  buffer (copy it to the snapshot buffer), and you can enable or disable
  an event to be traced when a function is hit.

   3) A perf clock has been added.

  A "perf" clock can be chosen to be used when tracing.  This will cause
  ftrace to use the same clock as perf uses, and hopefully this will
  make it easier to interleave the perf and ftrace data for analysis."

* tag 'trace-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (82 commits)
  tracepoints: Prevent null probe from being added
  tracing: Compare to 1 instead of zero for is_signed_type()
  tracing: Remove obsolete macro guard _TRACE_PROFILE_INIT
  ftrace: Get rid of ftrace_profile_bits
  tracing: Check return value of tracing_init_dentry()
  tracing: Get rid of unneeded key calculation in ftrace_hash_move()
  tracing: Reset ftrace_graph_filter_enabled if count is zero
  tracing: Fix off-by-one on allocating stat->pages
  kernel: tracing: Use strlcpy instead of strncpy
  tracing: Update debugfs README file
  tracing: Fix ftrace_dump()
  tracing: Rename trace_event_mutex to trace_event_sem
  tracing: Fix comment about prefix in arch_syscall_match_sym_name()
  tracing: Convert trace_destroy_fields() to static
  tracing: Move find_event_field() into trace_events.c
  tracing: Use TRACE_MAX_PRINT instead of constant
  tracing: Use pr_warn_once instead of open coded implementation
  ring-buffer: Add ring buffer startup selftest
  tracing: Bring Documentation/trace/ftrace.txt up to date
  tracing: Add "perf" trace_clock
  ...

Conflicts:
	kernel/trace/ftrace.c
	kernel/trace/trace.c
2013-04-29 13:55:38 -07:00
Steven Rostedt (Red Hat)
6c43e554a2 ring-buffer: Add ring buffer startup selftest
When testing my large changes to the ftrace system, there was
a bug that looked like the ring buffer was dropping events.
I wrote up a quick integrity checker of the ring buffer to
see if it was.

Although the bug ended up being something stupid I did in ftrace,
and had nothing to do with the ring buffer, I figured if I spent
the time to write up this test, I might as well include it in the
kernel.

I cleaned it up a bit, as the original version was rather ugly.
Not saying this version is pretty, but it's a beauty queen
compared to what I original wrote.

To enable the start up test, set CONFIG_RING_BUFFER_STARTUP_TEST.

Note, it runs for 10 seconds, so it will slow your boot time
by at least 10 more seconds.

What it does is documented in both the comments and the Kconfig
help.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-03-15 13:21:16 -04:00
Steven Rostedt (Red Hat)
f5eb558826 ring-buffer: Do not use schedule_work_on() for current CPU
The ring buffer updates when done while the ring buffer is active,
needs to be completed on the CPU that is used for the ring buffer
per_cpu buffer. To accomplish this, schedule_work_on() is used to
schedule work on the given CPU.

Now there's no reason to use schedule_work_on() if the process
doing the update happens to be on the CPU that it is processing.
It has already filled the requirement. Instead, just do the work
and continue.

This is needed for tracing_snapshot_alloc() where it may be called
really early in boot, where the work queues have not been set up yet.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-03-15 00:35:52 -04:00
Steven Rostedt (Red Hat)
f1dc672588 ring-buffer: Init waitqueue for blocked readers
The move of blocked readers to the ring buffer left out the
init of the wait queue that is used. Tests missed this due to running
stress tests against the buffers, which didn't allow for any
readers to end up waiting. Running a simple read and wait triggered
a bug.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-03-15 00:34:55 -04:00
Steven Rostedt (Red Hat)
15693458c4 tracing/ring-buffer: Move poll wake ups into ring buffer code
Move the logic to wake up on ring buffer data into the ring buffer
code itself. This simplifies the tracing code a lot and also has the
added benefit that waiters on one of the instance buffers can be woken
only when data is added to that instance instead of data added to
any instance.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-03-15 00:34:50 -04:00
Linus Torvalds
8fd5e7a2d9 ImgTec Meta architecture changes for v3.9-rc1
This adds core architecture support for Imagination's Meta processor
 cores, followed by some later miscellaneous arch/metag cleanups and
 fixes which I kept separate to ease review:
 
  - Support for basic Meta 1 (ATP) and Meta 2 (HTP) core architecture
  - A few fixes all over, particularly for symbol prefixes
  - A few privilege protection fixes
  - Several cleanups (setup.c includes, split out a lot of metag_ksyms.c)
  - Fix some missing exports
  - Convert hugetlb to use vm_unmapped_area()
  - Copy device tree to non-init memory
  - Provide dma_get_sgtable()
 
 Signed-off-by: James Hogan <james.hogan@imgtec.com>
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Merge tag 'metag-v3.9-rc1-v4' of git://git.kernel.org/pub/scm/linux/kernel/git/jhogan/metag

Pull new ImgTec Meta architecture from James Hogan:
 "This adds core architecture support for Imagination's Meta processor
  cores, followed by some later miscellaneous arch/metag cleanups and
  fixes which I kept separate to ease review:

   - Support for basic Meta 1 (ATP) and Meta 2 (HTP) core architecture
   - A few fixes all over, particularly for symbol prefixes
   - A few privilege protection fixes
   - Several cleanups (setup.c includes, split out a lot of
     metag_ksyms.c)
   - Fix some missing exports
   - Convert hugetlb to use vm_unmapped_area()
   - Copy device tree to non-init memory
   - Provide dma_get_sgtable()"

* tag 'metag-v3.9-rc1-v4' of git://git.kernel.org/pub/scm/linux/kernel/git/jhogan/metag: (61 commits)
  metag: Provide dma_get_sgtable()
  metag: prom.h: remove declaration of metag_dt_memblock_reserve()
  metag: copy devicetree to non-init memory
  metag: cleanup metag_ksyms.c includes
  metag: move mm/init.c exports out of metag_ksyms.c
  metag: move usercopy.c exports out of metag_ksyms.c
  metag: move setup.c exports out of metag_ksyms.c
  metag: move kick.c exports out of metag_ksyms.c
  metag: move traps.c exports out of metag_ksyms.c
  metag: move irq enable out of irqflags.h on SMP
  genksyms: fix metag symbol prefix on crc symbols
  metag: hugetlb: convert to vm_unmapped_area()
  metag: export clear_page and copy_page
  metag: export metag_code_cache_flush_all
  metag: protect more non-MMU memory regions
  metag: make TXPRIVEXT bits explicit
  metag: kernel/setup.c: sort includes
  perf: Enable building perf tools for Meta
  metag: add boot time LNKGET/LNKSET check
  metag: add __init to metag_cache_probe()
  ...
2013-03-03 12:06:09 -08:00
James Hogan
649508f684 trace/ring_buffer: handle 64bit aligned structs
Some 32 bit architectures require 64 bit values to be aligned (for
example Meta which has 64 bit read/write instructions). These require 8
byte alignment of event data too, so use
!CONFIG_HAVE_64BIT_ALIGNED_ACCESS instead of !CONFIG_64BIT ||
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS to decide alignment, and align
buffer_data_page::data accordingly.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org> (previous version subtly different)
2013-03-02 20:09:16 +00:00
Steven Rostedt (Red Hat)
ad964704ba ring-buffer: Add stats field for amount read from trace ring buffer
Add a stat about the number of events read from the ring buffer:

 #  cat /debug/tracing/per_cpu/cpu0/stats
entries: 39869
overrun: 870512
commit overrun: 0
bytes: 1449912
oldest event ts:  6561.368690
now ts:  6565.246426
dropped events: 0
read events: 112    <-- Added

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-01-30 11:01:53 -05:00
Steven Rostedt
0b07436d95 ring-buffer: Remove trace.h from ring_buffer.c
ring_buffer.c use to require declarations from trace.h, but
these have moved to the generic header files. There's nothing
in trace.h that ring_buffer.c requires.

There's some headers that trace.h included that ring_buffer.c
needs, but it's best that it includes them directly, and not
include trace.h.

Also, some things may use ring_buffer.c without having tracing
configured. This removes the dependency that may come in the
future.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-01-22 23:38:03 -05:00
Steven Rostedt
567cd4da54 ring-buffer: User context bit recursion checking
Using context bit recursion checking, we can help increase the
performance of the ring buffer.

Before this patch:

 # echo function > /debug/tracing/current_tracer
 # for i in `seq 10`; do ./hackbench 50; done
Time: 10.285
Time: 10.407
Time: 10.243
Time: 10.372
Time: 10.380
Time: 10.198
Time: 10.272
Time: 10.354
Time: 10.248
Time: 10.253

(average: 10.3012)

Now we have:

 # echo function > /debug/tracing/current_tracer
 # for i in `seq 10`; do ./hackbench 50; done
Time: 9.712
Time: 9.824
Time: 9.861
Time: 9.827
Time: 9.962
Time: 9.905
Time: 9.886
Time: 10.088
Time: 9.861
Time: 9.834

(average: 9.876)

 a 4% savings!

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-01-22 23:38:03 -05:00
Steven Rostedt
771e03842a ring-buffer: Remove unnecessary recusive call in rb_advance_iter()
The original ring-buffer code had special checks at the start
of rb_advance_iter() and instead of repeating them again at the
end of the function if a certain condition existed, I just did
a recursive call to rb_advance_iter() because the special condition
would cause rb_advance_iter() to return early (after the checks).

But as things have changed, the special checks no longer exist
and the only thing done for the special_condition is to call
rb_inc_iter() and return. Instead of doing a confusing recursive call,
just call rb_inc_iter instead.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2013-01-21 13:22:29 -05:00
Linus Torvalds
da830e589a Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull perf fixes from Ingo Molnar:
 "These are late-v3.7 pending fixes for tracing."

Fix up trivial conflict in kernel/trace/ring_buffer.c: the NULL pointer
fix clashed with the change of type of the 'ret' variable.

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  ring-buffer: Fix race between integrity check and readers
  ring-buffer: Fix NULL pointer if rb_set_head_page() fails
  ftrace: Clear bits properly in reset_iter_read()
2012-12-11 18:18:58 -08:00
Steven Rostedt
9366c1ba13 ring-buffer: Fix race between integrity check and readers
The function rb_check_pages() was added to make sure the ring buffer's
pages were sane. This check is done when the ring buffer size is modified
as well as when the iterator is released (closing the "trace" file),
as that was considered a non fast path and a good place to do a sanity
check.

The problem is that the check does not have any locks around it.
If one process were to read the trace file, and another were to read
the raw binary file, the check could happen while the reader is reading
the file.

The issues with this is that the check requires to clear the HEAD page
before doing the full check and it restores it afterward. But readers
require the HEAD page to exist before it can read the buffer, otherwise
it gives a nasty warning and disables the buffer.

By adding the reader lock around the check, this keeps the race from
happening.

Cc: stable@vger.kernel.org # 3.6
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-11-30 11:09:57 -05:00
Steven Rostedt
54f7be5b83 ring-buffer: Fix NULL pointer if rb_set_head_page() fails
The function rb_set_head_page() searches the list of ring buffer
pages for a the page that has the HEAD page flag set. If it does
not find it, it will do a WARN_ON(), disable the ring buffer and
return NULL, as this should never happen.

But if this bug happens to happen, not all callers of this function
can handle a NULL pointer being returned from it. That needs to be
fixed.

Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-11-30 11:09:28 -05:00
Yoshihiro YUNOMAE
50ecf2c3af ring-buffer: Change unsigned long type of ring_buffer_oldest_event_ts() to u64
ring_buffer_oldest_event_ts() should return a value of u64 type, because
ring_buffer_per_cpu->buffer_page->buffer_data_page->time_stamp is u64 type.

Link: http://lkml.kernel.org/r/1349998076-15495-5-git-send-email-dhsharp@google.com

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Signed-off-by: David Sharp <dhsharp@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-11-02 10:21:48 -04:00
David Sharp
01e3e710a9 tracing: Trivial cleanup
Remove ftrace_format_syscall() declaration; it is neither defined nor
used. Also update a comment and formatting.

Link: http://lkml.kernel.org/r/1339112785-21806-1-git-send-email-vnagarnaik@google.com

Signed-off-by: David Sharp <dhsharp@google.com>
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-10-31 16:45:33 -04:00
Slava Pestov
884bfe89a4 ring-buffer: Add a 'dropped events' counter
The existing 'overrun' counter is incremented when the ring
buffer wraps around, with overflow on (the default). We wanted
a way to count requests lost from the buffer filling up with
overflow off, too. I decided to add a new counter instead
of retro-fitting the existing one because it seems like a
different statistic to count conceptually, and also because
of how the code was structured.

Link: http://lkml.kernel.org/r/1310765038-26399-1-git-send-email-slavapestov@google.com

Signed-off-by: Slava Pestov <slavapestov@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-10-31 16:45:27 -04:00
Vaibhav Nagarnaik
8e49f418c9 ring-buffer: Check for uninitialized cpu buffer before resizing
With a system where, num_present_cpus < num_possible_cpus, even if all
CPUs are online, non-present CPUs don't have per_cpu buffers allocated.
If per_cpu/<cpu>/buffer_size_kb is modified for such a CPU, it can cause
a panic due to NULL dereference in ring_buffer_resize().

To fix this, resize operation is allowed only if the per-cpu buffer has
been initialized.

Link: http://lkml.kernel.org/r/1349912427-6486-1-git-send-email-vnagarnaik@google.com

Cc: stable@vger.kernel.org # 3.5+
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2012-10-11 12:21:48 -04:00