Fix the problem of protecting the kgdb handle_exception exit
which had an NMI race condition, while trying to restore
normal system operation.
There was a small window after the master processor sets cpu_in_debug
to zero but before it has set kgdb_active to zero where a
non-master processor in an SMP system could receive an NMI and
re-enter the kgdb_wait() loop.
As long as the master processor sets the cpu_in_debug before sending
the cpu roundup the cpu_in_debug variable can also be used to guard
against the race condition.
The kgdb_wait() function no longer needs to check
kgdb_active because it is done in the arch specific code
and handled along with the nmi traps at the low level.
This also allows kgdb_wait() to exit correctly if it was
entered for some unknown reason due to a spurious NMI that
could not be handled by the arch specific code.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kgdb core fixes:
- Check to see that mm->mmap_cache is not null before calling
flush_cache_range(), else on arch=ARM it will cause a fatal
fault.
- Breakpoints should only be restored if they are in the BP_ACTIVE
state.
- Fix a typo in comments to "kgdb_register_io_module"
x86 kgdb fixes:
- Fix the x86 arch handler such that on a kill or detach that the
appropriate cleanup on the single stepping flags gets run.
- Add in the DIE_NMIWATCHDOG call for x86_64
- Touch the nmi watchdog before returning the system to normal
operation after performing any kind of kgdb operation, else
the possibility exists to trigger the watchdog.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Fix two regressions dealing with the kgdb core.
1) kgdb_skipexception and kgdb_post_primary_code are optional
functions that are only required on archs that need special exception
fixups.
2) The kernel address space scope must be set on any probe_kernel_*
function or archs such as ARCH=arm will not allow access to the kernel
memory space. As an example, it is required to allow the full kernel
address space is when you the kernel debugger to inspect a system
call.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Add HW breakpoints into the arch specific portion of x86 kgdb. In the
current x86 kernel.org kernels HW breakpoints are changed out in lazy
fashion because there is no infrastructure around changing them when
changing to a kernel task or entering the kernel mode via a system
call. This lazy approach means that if a user process uses HW
breakpoints the kgdb will loose out. This is an acceptable trade off
because the developer debugging the kernel is assumed to know what is
going on system wide and would be aware of this trade off.
There is a minor bug fix to the kgdb core so as to correctly call the
hw breakpoint functions with a valid value from the enum.
There is also a minor change to the x86_64 startup code when using
early HW breakpoints. When the debugger is connected, the cpu startup
code must not zero out the HW breakpoint registers or you cannot hit
the breakpoints you are interested in, in the first place.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
If kgdb does remove a breakpoint that had a problem on the recursion
check, it should also print the address of the breakpoint.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
In order to not trip the clocksource watchdog, kgdb must touch the
clocksource watchdog on the return to normal system run state.
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kgdb core code. Handles the protocol and the arch details.
[ mingo@elte.hu: heavily modified, simplified and cleaned up. ]
[ xemul@openvz.org: use find_task_by_pid_ns ]
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
When I cleaned up printk() and split up the printk locking logic in
commit 266c2e0abe ("Make printk() console
semaphore accesses sensible") I had incorrectly moved the call to
have_callable_console() outside of the console semaphore.
That was buggy. The console semaphore protects the console_drivers list
that is used by have_callable_console().
Thanks go to Bongani Hlope who saw this as a hang on shutdown and reboot
and bisected the bug to the right commit, and tested this patch. See
http://lkml.org/lkml/2008/4/11/315
Bisected-and-tested-by: Bongani Hlope <bonganilinux@mweb.co.za>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
revert "sched: fix fair sleepers" (e22ecef1d2),
because it is causing audio skipping, see:
http://bugzilla.kernel.org/show_bug.cgi?id=10428
the patch is correct and the real cause of the skipping is not
understood (tracing makes it go away), but time has run out so we'll
revert it and re-try in 2.6.26.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Extend the /proc/<pid>/cgroup file to include the appropriate hierarchy ID on
each line.
Currently this ID isn't really needed since a hierarchy can be completely
identified by the set of subsystems bound to it, but this is likely to change
in the near future in order to support stateless subsystems and
merging/rebinding of subsystems. Getting this change into 2.6.25 reduces the
need for an API change later.
Signed-off-by: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The prevent_tail_call() macro works around the problem of the compiler
clobbering argument words on the stack, which for asmlinkage functions
is the caller's (user's) struct pt_regs. The tail/sibling-call
optimization is not the only way that the compiler can decide to use
stack argument words as scratch space, which we have to prevent.
Other optimizations can do it too.
Until we have new compiler support to make "asmlinkage" binding on the
compiler's own use of the stack argument frame, we have work around all
the manifestations of this issue that crop up.
More cases seem to be prevented by also keeping the incoming argument
variables live at the end of the function. This makes their original
stack slots attractive places to leave those variables, so the compiler
tends not clobber them for something else. It's still no guarantee, but
it handles some observed cases that prevent_tail_call() did not.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The effects of cgroup_disable=foo are:
- foo isn't auto-mounted if you mount all cgroups in a single hierarchy
- foo isn't visible as an individually mountable subsystem
As a result there will only ever be one call to foo->create(), at init time;
all processes will stay in this group, and the group will never be mounted on
a visible hierarchy. Any additional effects (e.g. not allocating metadata)
are up to the foo subsystem.
This doesn't handle early_init subsystems (their "disabled" bit isn't set be,
but it could easily be extended to do so if any of the early_init systems
wanted it - I think it would just involve some nastier parameter processing
since it would occur before the command-line argument parser had been run.
Hugh said:
Ballpark figures, I'm trying to get this question out rather than
processing the exact numbers: CONFIG_CGROUP_MEM_RES_CTLR adds 15% overhead
to the affected paths, booting with cgroup_disable=memory cuts that back to
1% overhead (due to slightly bigger struct page).
I'm no expert on distros, they may have no interest whatever in
CONFIG_CGROUP_MEM_RES_CTLR=y; and the rest of us can easily build with or
without it, or apply the cgroup_disable=memory patches.
Unix bench's execl test result on x86_64 was
== just after boot without mounting any cgroup fs.==
mem_cgorup=off : Execl Throughput 43.0 3150.1 732.6
mem_cgroup=on : Execl Throughput 43.0 2932.6 682.0
==
[lizf@cn.fujitsu.com: fix boot option parsing]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Sudhir Kumar <skumar@linux.vnet.ibm.com>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Markers do not mix well with CONFIG_PREEMPT_RCU because it uses
preempt_disable/enable() and not rcu_read_lock/unlock for minimal
intrusiveness. We would need call_sched and sched_barrier primitives.
Currently, the modification (connection and disconnection) of probes
from markers requires changes to the data structure done in RCU-style :
a new data structure is created, the pointer is changed atomically, a
quiescent state is reached and then the old data structure is freed.
The quiescent state is reached once all the currently running
preempt_disable regions are done running. We use the call_rcu mechanism
to execute kfree() after such quiescent state has been reached.
However, the new CONFIG_PREEMPT_RCU version of call_rcu and rcu_barrier
does not guarantee that all preempt_disable code regions have finished,
hence the race.
The "proper" way to do this is to use rcu_read_lock/unlock, but we don't
want to use it to minimize intrusiveness on the traced system. (we do
not want the marker code to call into much of the OS code, because it
would quickly restrict what can and cannot be instrumented, such as the
scheduler).
The temporary fix, until we get call_rcu_sched and rcu_barrier_sched in
mainline, is to use synchronize_sched before each call_rcu calls, so we
wait for the quiescent state in the system call code path. It will slow
down batch marker enable/disable, but will make sure the race is gone.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Silence two kerneldoc warnings.
Warning(kernel/audit.c:1276): No description found for parameter 'string'
Warning(kernel/audit.c:1276): No description found for parameter 'len'
[also fix a typo for bonus points]
Signed-off-by: Dave Jones <davej@codemonkey.org.uk>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The futex init function is called init(). This is a pain in the neck
when debugging when you code dies in ... init :-)
This renames it to futex_init().
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/linux-2.6-hrt:
NOHZ: reevaluate idle sleep length after add_timer_on()
clocksource: revert: use init_timer_deferrable for clocksource_watchdog
relay doesn't reference the pages it adds, however we need a non-NULL
hook or splice_to_pipe() can oops.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
I found that relay files can be read by pread(2). I fix it,
for relay files are not capable of seeking.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
add_timer_on() can add a timer on a CPU which is currently in a long
idle sleep, but the timer wheel is not reevaluated by the nohz code on
that CPU. So a timer can be delayed for quite a long time. This
triggered a false positive in the clocksource watchdog code.
To avoid this we need to wake up the idle CPU and enforce the
reevaluation of the timer wheel for the next timer event.
Add a function, which checks a given CPU for idle state, marks the
idle task with NEED_RESCHED and sends a reschedule IPI to notify the
other CPU of the change in the timer wheel.
Call this function from add_timer_on().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: stable@kernel.org
--
include/linux/sched.h | 6 ++++++
kernel/sched.c | 43 +++++++++++++++++++++++++++++++++++++++++++
kernel/timer.c | 10 +++++++++-
3 files changed, 58 insertions(+), 1 deletion(-)
Revert
commit 1077f5a917
Author: Parag Warudkar <parag.warudkar@gmail.com>
Date: Wed Jan 30 13:30:01 2008 +0100
clocksource.c: use init_timer_deferrable for clocksource_watchdog
clocksource_watchdog can use a deferrable timer - reduces wakeups from
idle per second.
The watchdog timer needs to run with the specified interval. Otherwise
it will miss the possible wrap of the watchdog clocksource.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
The printk() logic on when/how to get the console semaphore was
unreadable, this splits the code up into a few helper functions and
makes it easier to follow what is going on.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In case we're accounting from a sub-namespace, the tgids reported will not
refer to the right namespace.
Save the pid_namespace we're accounting in on the acct_glbs and use it in
do_acct_process.
Two less :) places using the task_struct.tgid member.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is minor, but dereferencing even current real_parent is not safe on debug
kernels, since the memory, this points to, can be unmapped - RCU protection is
required.
Besides, the tgid field is deprecated and is to be replaced with task_tgid_xxx
call (the 2nd patch), so RCU will be required anyway.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
As Paul pointed out, the ACCESS_ONCE are not needed because we already have
the explicit surrounding memory barriers.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Mason <mmlnx@us.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: David Smith <dsmith@redhat.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Adrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add comments requested by Andrew.
Updated comments about synchronize_sched(). Since we use call_rcu and
rcu_barrier now, these comments were out of sync with the code.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Mason <mmlnx@us.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: David Smith <dsmith@redhat.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Adrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The printk() can deadlock because it can wake up klogd(), and
task enqueueing will try to read the time in order to set a hrtimer.
Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Debugged-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Will be called each time the scheduling domains are rebuild.
Needed for architectures that don't have a static cpu topology.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Needed so it can be called from outside of sched.c.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
TREE_AVG and APPROX_AVG are initial task placement policies that have been
disabled for a long while.. time to remove them.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
From: Pavel Emelyanov <xemul@openvz.org>
This patch is based on the one from Thomas.
The kauditd_thread() calls the netlink_unicast() and passes
the audit_pid to it. The audit_pid, in turn, is received from
the user space and the tool (I've checked the audit v1.6.9)
uses getpid() to pass one in the kernel. Besides, this tool
doesn't bind the netlink socket to this id, but simply creates
it allowing the kernel to auto-bind one.
That's the preamble.
The problem is that netlink_autobind() _does_not_ guarantees
that the socket will be auto-bound to the current pid. Instead
it uses the current pid as a hint to start looking for a free
id. So, in case of conflict, the audit messages can be sent
to a wrong socket. This can happen (it's unlikely, but can be)
in case some task opens more than one netlink sockets and then
the audit one starts - in this case the audit's pid can be busy
and its socket will be bound to another id.
The proposal is to introduce an audit_nlk_pid in audit subsys,
that will point to the netlink socket to send packets to. It
will most often be equal to audit_pid. The socket id can be
got from the skb's netlink CB right in the audit_receive_msg.
The audit_nlk_pid reset to 0 is not required, since all the
decisions are taken based on audit_pid value only.
Later, if the audit tools will bind the socket themselves, the
kernel will have to provide a way to setup the audit_nlk_pid
as well.
A good side effect of this patch is that audit_pid can later
be converted to struct pid, as it is not longer safe to use
pid_t-s in the presence of pid namespaces. But audit code still
uses the tgid from task_struct in the audit_signal_info and in
the audit_filter_syscall.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Revert commit 1ada5cba6a ("clocksource:
make clocksource watchdog cycle through online CPUs") due to the
regression reported by Gabriel C at
http://lkml.org/lkml/2008/2/24/281
(short vesion: it makes TSC be marked as always unstable on his
machine).
Cc: Andi Kleen <ak@suse.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Robert Hancock <hancockr@shaw.ca>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Gabriel C <nix.or.die@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Wakeup-buddy tasks are cache-hot - this makes it a bit harder
for the load-balancer to tear them apart. (but it's still possible,
if the load is sufficiently assymetric)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
improve affine wakeups. Maintain the 'overlap' metric based on CFS's
sum_exec_runtime - which means the amount of time a task executes
after it wakes up some other task.
Use the 'overlap' for the wakeup decisions: if the 'overlap' is short,
it means there's strong workload coupling between this task and the
woken up task. If the 'overlap' is large then the workload is decoupled
and the scheduler will move them to separate CPUs more easily.
( Also slightly move the preempt_check within try_to_wake_up() - this has
no effect on functionality but allows 'early wakeups' (for still-on-rq
tasks) to be correctly accounted as well.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
split out the affine-wakeup bits.
No code changed:
kernel/sched.o:
text data bss dec hex filename
42521 2858 232 45611 b22b sched.o.before
42521 2858 232 45611 b22b sched.o.after
md5:
9d76738f1272aa82f0b7affd2f51df6b sched.o.before.asm
09b31c44e9aff8666f72773dc433e2df sched.o.after.asm
(the md5's changed because stack slots changed and some registers
get scheduled by gcc in a different order - but otherwise the before
and after assembly is instruction for instruction equivalent.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
If subbuf_pages was larger than the max number of pages the pipe
buffer will hold, subbuf_splice_actor() would happily go beyond
the array size.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Use the existing calc_delta_mine() calculation for sched_slice(). This
saves a divide and simplifies the code because we share it with the
other /cfs_rq->load users.
It also improves code size:
text data bss dec hex filename
42659 2740 144 45543 b1e7 sched.o.before
42093 2740 144 44977 afb1 sched.o.after
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Fair sleepers need to scale their latency target down by runqueue
weight. Otherwise busy systems will gain ever larger sleep bonus.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Currently we schedule to the leftmost task in the runqueue. When the
runtimes are very short because of some server/client ping-pong,
especially in over-saturated workloads, this will cycle through all
tasks trashing the cache.
Reduce cache trashing by keeping dependent tasks together by running
newly woken tasks first. However, by not running the leftmost task first
we could starve tasks because the wakee can gain unlimited runtime.
Therefore we only run the wakee if its within a small
(wakeup_granularity) window of the leftmost task. This preserves
fairness, but does alternate server/client task groups.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Clear the cached inverse value when updating load. This is needed for
calc_delta_mine() to work correctly when using the rq load.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Current min_vruntime tracking is incorrect and will cause serious
problems when we don't run the leftmost task for some reason.
min_vruntime does two things; 1) it's used to determine a forward
direction when the u64 vruntime wraps, 2) it's used to track the
leftmost vruntime to position newly enqueued tasks from.
The current logic advances min_vruntime whenever the current task's
vruntime advance. Because the current task may pass the leftmost task
still waiting we're failing the second goal. This causes new tasks to be
placed too far ahead and thus penalizes their runtime.
Fix this by making min_vruntime the min_vruntime of the waiting tasks by
tracking it in enqueue/dequeue, and compare against current's vruntime
to obtain the absolute minimum when placing new tasks.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Fix a hard to trigger crash seen in the -rt kernel that also affects
the vanilla scheduler.
There is a race condition between schedule() and some dequeue/enqueue
functions; rt_mutex_setprio(), __setscheduler() and sched_move_task().
When scheduling to idle, idle_balance() is called to pull tasks from
other busy processor. It might drop the rq lock. It means that those 3
functions encounter on_rq=0 and running=1. The current task should be
put when running.
Here is a possible scenario:
CPU0 CPU1
| schedule()
| ->deactivate_task()
| ->idle_balance()
| -->load_balance_newidle()
rt_mutex_setprio() |
| --->double_lock_balance()
*get lock *rel lock
* on_rq=0, ruuning=1 |
* sched_class is changed |
*rel lock *get lock
: |
:
->put_prev_task_rt()
->pick_next_task_fair()
=> panic
The current process of CPU1(P1) is scheduling. Deactivated P1, and the
scheduler looks for another process on other CPU's runqueue because CPU1
will be idle. idle_balance(), load_balance_newidle() and
double_lock_balance() are called and double_lock_balance() could drop
the rq lock. On the other hand, CPU0 is trying to boost the priority of
P1. The result of boosting only P1's prio and sched_class are changed to
RT. The sched entities of P1 and P1's group are never put. It makes
cfs_rq invalid, because the cfs_rq has curr and no leaf, but
pick_next_task_fair() is called, then the kernel panics.
Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
