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With the new ORC unwinder, ftrace stack tracing became disfunctional.

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One was that ORC didn't know how to handle the ftrace callbacks in general
 (which Josh fixed). The other was that ORC would just bail if it hit a
 dynamically allocated trampoline. Which means all ftrace stack tracing that
 happens from the function tracer would produce no results (that includes
 killing the max stack size tracer).  I added a check to the ORC unwinder to
 see if the trampoline belonged to ftrace, and if it did, use the orc entry
 of the static trampoline that was used to create the dynamic one (it would
 be identical).
 
 Finally, I noticed that the skip values of the stack tracing were out of
 whack. I went through and fixed them up.
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Merge tag 'trace-v4.15-rc9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "With the new ORC unwinder, ftrace stack tracing became disfunctional.

  One was that ORC didn't know how to handle the ftrace callbacks in
  general (which Josh fixed).

  The other was that ORC would just bail if it hit a dynamically
  allocated trampoline. Which means all ftrace stack tracing that
  happens from the function tracer would produce no results (that
  includes killing the max stack size tracer). I added a check to the
  ORC unwinder to see if the trampoline belonged to ftrace, and if it
  did, use the orc entry of the static trampoline that was used to
  create the dynamic one (it would be identical).

  Finally, I noticed that the skip values of the stack tracing were out
  of whack. I went through and fixed them up"

* tag 'trace-v4.15-rc9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Update stack trace skipping for ORC unwinder
  ftrace, orc, x86: Handle ftrace dynamically allocated trampolines
  x86/ftrace: Fix ORC unwinding from ftrace handlers
This commit is contained in:
Linus Torvalds 2018-01-24 10:08:16 -08:00
commit 03fae44b41
8 changed files with 155 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/kernel/Makefile
View File

@ -29,10 +29,13 @@ KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_test_nx.o := y
OBJECT_FILES_NON_STANDARD_paravirt_patch_$(BITS).o := y
ifdef CONFIG_FRAME_POINTER
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
endif
# If instrumentation of this dir is enabled, boot hangs during first second.
# Probably could be more selective here, but note that files related to irqs,
# boot, dumpstack/stacktrace, etc are either non-interesting or can lead to

24
arch/x86/kernel/ftrace_64.S
View File

@ -8,6 +8,7 @@
#include <asm/ftrace.h>
#include <asm/export.h>
#include <asm/nospec-branch.h>
#include <asm/unwind_hints.h>
.code64
.section .entry.text, "ax"
@ -20,7 +21,6 @@ EXPORT_SYMBOL(__fentry__)
EXPORT_SYMBOL(mcount)
#endif
/* All cases save the original rbp (8 bytes) */
#ifdef CONFIG_FRAME_POINTER
# ifdef CC_USING_FENTRY
/* Save parent and function stack frames (rip and rbp) */
@ -31,7 +31,7 @@ EXPORT_SYMBOL(mcount)
# endif
#else
/* No need to save a stack frame */
# define MCOUNT_FRAME_SIZE 8
# define MCOUNT_FRAME_SIZE 0
#endif /* CONFIG_FRAME_POINTER */
/* Size of stack used to save mcount regs in save_mcount_regs */
@ -64,10 +64,10 @@ EXPORT_SYMBOL(mcount)
*/
.macro save_mcount_regs added=0
/* Always save the original rbp */
#ifdef CONFIG_FRAME_POINTER
/* Save the original rbp */
pushq %rbp
#ifdef CONFIG_FRAME_POINTER
/*
* Stack traces will stop at the ftrace trampoline if the frame pointer
* is not set up properly. If fentry is used, we need to save a frame
@ -105,7 +105,11 @@ EXPORT_SYMBOL(mcount)
* Save the original RBP. Even though the mcount ABI does not
* require this, it helps out callers.
*/
#ifdef CONFIG_FRAME_POINTER
movq MCOUNT_REG_SIZE-8(%rsp), %rdx
#else
movq %rbp, %rdx
#endif
movq %rdx, RBP(%rsp)
/* Copy the parent address into %rsi (second parameter) */
@ -148,7 +152,7 @@ EXPORT_SYMBOL(mcount)
ENTRY(function_hook)
retq
END(function_hook)
ENDPROC(function_hook)
ENTRY(ftrace_caller)
/* save_mcount_regs fills in first two parameters */
@ -184,7 +188,7 @@ GLOBAL(ftrace_graph_call)
/* This is weak to keep gas from relaxing the jumps */
WEAK(ftrace_stub)
retq
END(ftrace_caller)
ENDPROC(ftrace_caller)
ENTRY(ftrace_regs_caller)
/* Save the current flags before any operations that can change them */
@ -255,7 +259,7 @@ GLOBAL(ftrace_regs_caller_end)
jmp ftrace_epilogue
END(ftrace_regs_caller)
ENDPROC(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
@ -313,9 +317,10 @@ ENTRY(ftrace_graph_caller)
restore_mcount_regs
retq
END(ftrace_graph_caller)
ENDPROC(ftrace_graph_caller)
GLOBAL(return_to_handler)
ENTRY(return_to_handler)
UNWIND_HINT_EMPTY
subq $24, %rsp
/* Save the return values */
@ -330,4 +335,5 @@ GLOBAL(return_to_handler)
movq (%rsp), %rax
addq $24, %rsp
JMP_NOSPEC %rdi
END(return_to_handler)
#endif

48
arch/x86/kernel/unwind_orc.c
View File

@ -74,8 +74,50 @@ static struct orc_entry *orc_module_find(unsigned long ip)
}
#endif
#ifdef CONFIG_DYNAMIC_FTRACE
static struct orc_entry *orc_find(unsigned long ip);
/*
* Ftrace dynamic trampolines do not have orc entries of their own.
* But they are copies of the ftrace entries that are static and
* defined in ftrace_*.S, which do have orc entries.
*
* If the undwinder comes across a ftrace trampoline, then find the
* ftrace function that was used to create it, and use that ftrace
* function's orc entrie, as the placement of the return code in
* the stack will be identical.
*/
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
struct ftrace_ops *ops;
unsigned long caller;
ops = ftrace_ops_trampoline(ip);
if (!ops)
return NULL;
if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
caller = (unsigned long)ftrace_regs_call;
else
caller = (unsigned long)ftrace_call;
/* Prevent unlikely recursion */
if (ip == caller)
return NULL;
return orc_find(caller);
}
#else
static struct orc_entry *orc_ftrace_find(unsigned long ip)
{
return NULL;
}
#endif
static struct orc_entry *orc_find(unsigned long ip)
{
static struct orc_entry *orc;
if (!orc_init)
return NULL;
@ -111,7 +153,11 @@ static struct orc_entry *orc_find(unsigned long ip)
__stop_orc_unwind_ip - __start_orc_unwind_ip, ip);
/* Module lookup: */
return orc_module_find(ip);
orc = orc_module_find(ip);
if (orc)
return orc;
return orc_ftrace_find(ip);
}
static void orc_sort_swap(void *_a, void *_b, int size)

2
include/linux/ftrace.h
View File

@ -332,6 +332,8 @@ extern int ftrace_text_reserved(const void *start, const void *end);
extern int ftrace_nr_registered_ops(void);
struct ftrace_ops *ftrace_ops_trampoline(unsigned long addr);
bool is_ftrace_trampoline(unsigned long addr);
/*

29
kernel/trace/ftrace.c
View File

@ -1119,15 +1119,11 @@ static struct ftrace_ops global_ops = {
};
/*
* This is used by __kernel_text_address() to return true if the
* address is on a dynamically allocated trampoline that would
* not return true for either core_kernel_text() or
* is_module_text_address().
* Used by the stack undwinder to know about dynamic ftrace trampolines.
*/
bool is_ftrace_trampoline(unsigned long addr)
struct ftrace_ops *ftrace_ops_trampoline(unsigned long addr)
{
struct ftrace_ops *op;
bool ret = false;
struct ftrace_ops *op = NULL;
/*
* Some of the ops may be dynamically allocated,
@ -1144,15 +1140,24 @@ bool is_ftrace_trampoline(unsigned long addr)
if (op->trampoline && op->trampoline_size)
if (addr >= op->trampoline &&
addr < op->trampoline + op->trampoline_size) {
ret = true;
goto out;
preempt_enable_notrace();
return op;
}
} while_for_each_ftrace_op(op);
out:
preempt_enable_notrace();
return ret;
return NULL;
}
/*
* This is used by __kernel_text_address() to return true if the
* address is on a dynamically allocated trampoline that would
* not return true for either core_kernel_text() or
* is_module_text_address().
*/
bool is_ftrace_trampoline(unsigned long addr)
{
return ftrace_ops_trampoline(addr) != NULL;
}
struct ftrace_page {

34
kernel/trace/trace.c
View File

@ -2374,6 +2374,15 @@ void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
}
EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
/*
* Skip 3:
*
* trace_buffer_unlock_commit_regs()
* trace_event_buffer_commit()
* trace_event_raw_event_xxx()
*/
# define STACK_SKIP 3
void trace_buffer_unlock_commit_regs(struct trace_array *tr,
struct ring_buffer *buffer,
struct ring_buffer_event *event,
@ -2383,16 +2392,12 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr,
__buffer_unlock_commit(buffer, event);
/*
* If regs is not set, then skip the following callers:
* trace_buffer_unlock_commit_regs
* event_trigger_unlock_commit
* trace_event_buffer_commit
* trace_event_raw_event_sched_switch
* If regs is not set, then skip the necessary functions.
* Note, we can still get here via blktrace, wakeup tracer
* and mmiotrace, but that's ok if they lose a function or
* two. They are that meaningful.
* two. They are not that meaningful.
*/
ftrace_trace_stack(tr, buffer, flags, regs ? 0 : 4, pc, regs);
ftrace_trace_stack(tr, buffer, flags, regs ? 0 : STACK_SKIP, pc, regs);
ftrace_trace_userstack(buffer, flags, pc);
}
@ -2579,11 +2584,13 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
trace.skip = skip;
/*
* Add two, for this function and the call to save_stack_trace()
* Add one, for this function and the call to save_stack_trace()
* If regs is set, then these functions will not be in the way.
*/
#ifndef CONFIG_UNWINDER_ORC
if (!regs)
trace.skip += 2;
trace.skip++;
#endif
/*
* Since events can happen in NMIs there's no safe way to
@ -2711,11 +2718,10 @@ void trace_dump_stack(int skip)
local_save_flags(flags);
/*
* Skip 3 more, seems to get us at the caller of
* this function.
*/
skip += 3;
#ifndef CONFIG_UNWINDER_ORC
/* Skip 1 to skip this function. */
skip++;
#endif
__ftrace_trace_stack(global_trace.trace_buffer.buffer,
flags, skip, preempt_count(), NULL);
}

17
kernel/trace/trace_events_trigger.c
View File

@ -1123,13 +1123,22 @@ static __init int register_trigger_snapshot_cmd(void) { return 0; }
#endif /* CONFIG_TRACER_SNAPSHOT */
#ifdef CONFIG_STACKTRACE
/*
* Skip 3:
* stacktrace_trigger()
#ifdef CONFIG_UNWINDER_ORC
/* Skip 2:
* event_triggers_post_call()
* trace_event_raw_event_xxx()
*/
#define STACK_SKIP 3
# define STACK_SKIP 2
#else
/*
* Skip 4:
* stacktrace_trigger()
* event_triggers_post_call()
* trace_event_buffer_commit()
* trace_event_raw_event_xxx()
*/
#define STACK_SKIP 4
#endif
static void
stacktrace_trigger(struct event_trigger_data *data, void *rec)

51
kernel/trace/trace_functions.c
View File

@ -154,6 +154,24 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
preempt_enable_notrace();
}
#ifdef CONFIG_UNWINDER_ORC
/*
* Skip 2:
*
* function_stack_trace_call()
* ftrace_call()
*/
#define STACK_SKIP 2
#else
/*
* Skip 3:
* __trace_stack()
* function_stack_trace_call()
* ftrace_call()
*/
#define STACK_SKIP 3
#endif
static void
function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct pt_regs *pt_regs)
@ -180,15 +198,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
if (likely(disabled == 1)) {
pc = preempt_count();
trace_function(tr, ip, parent_ip, flags, pc);
/*
* skip over 5 funcs:
* __ftrace_trace_stack,
* __trace_stack,
* function_stack_trace_call
* ftrace_list_func
* ftrace_call
*/
__trace_stack(tr, flags, 5, pc);
__trace_stack(tr, flags, STACK_SKIP, pc);
}
atomic_dec(&data->disabled);
@ -367,14 +377,27 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
tracer_tracing_off(tr);
}
#ifdef CONFIG_UNWINDER_ORC
/*
* Skip 4:
* ftrace_stacktrace()
* Skip 3:
*
* function_trace_probe_call()
* ftrace_ops_list_func()
* ftrace_ops_assist_func()
* ftrace_call()
*/
#define STACK_SKIP 4
#define FTRACE_STACK_SKIP 3
#else
/*
* Skip 5:
*
* __trace_stack()
* ftrace_stacktrace()
* function_trace_probe_call()
* ftrace_ops_assist_func()
* ftrace_call()
*/
#define FTRACE_STACK_SKIP 5
#endif
static __always_inline void trace_stack(struct trace_array *tr)
{
@ -384,7 +407,7 @@ static __always_inline void trace_stack(struct trace_array *tr)
local_save_flags(flags);
pc = preempt_count();
__trace_stack(tr, flags, STACK_SKIP, pc);
__trace_stack(tr, flags, FTRACE_STACK_SKIP, pc);
}
static void