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| author |   Steven Rostedt <srostedt@redhat.com> | 2012-05-30 13:26:37 -0400 |
|---|---|---|
| committer |   Steven Rostedt <rostedt@goodmis.org> | 2012-05-31 23:12:17 -0400 |
| commit | a192cd0413b71c2a3e4e48dd365af704be72b748 (patch) | |
| tree | 739c64a3fd4bf58b7c34a9eb5bc83aa844a06bf3 /arch/x86/kernel/traps.c | |
| parent | Merge tag 'perf-urgent-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/urgent (diff) | |
| download | linux-dev-a192cd0413b71c2a3e4e48dd365af704be72b748.tar.xz linux-dev-a192cd0413b71c2a3e4e48dd365af704be72b748.zip | |
ftrace: Synchronize variable setting with breakpoints
When the function tracer starts modifying the code via breakpoints
it sets a variable (modifying_ftrace_code) to inform the breakpoint
handler to call the ftrace int3 code.
But there's no synchronization between setting this code and the
handler, thus it is possible for the handler to be called on another
CPU before it sees the variable. This will cause a kernel crash as
the int3 handler will not know what to do with it.
I originally added smp_mb()'s to force the visibility of the variable
but H. Peter Anvin suggested that I just make it atomic.
[ Added comments as suggested by Peter Zijlstra ]
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to '')
| -rw-r--r-- | arch/x86/kernel/traps.c | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index ff08457a025d..05b31d92f69c 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -303,8 +303,12 @@ gp_in_kernel: dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_code) { #ifdef CONFIG_DYNAMIC_FTRACE - /* ftrace must be first, everything else may cause a recursive crash */ - if (unlikely(modifying_ftrace_code) && ftrace_int3_handler(regs)) + /* + * ftrace must be first, everything else may cause a recursive crash. + * See note by declaration of modifying_ftrace_code in ftrace.c + */ + if (unlikely(atomic_read(&modifying_ftrace_code)) && + ftrace_int3_handler(regs)) return; #endif #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP |