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tracing: Fix stacktrace skip depth in trace_buffer_unlock_commit_regs() 

While cleaning the stacktrace code I unintentially changed the skip depth of
trace_buffer_unlock_commit_regs() from 0 to 6. kprobes uses this function,
and with skipping 6 call backs, it can easily produce no stack.

Here's how I tested it:

 # echo 'p:ext4_sync_fs ext4_sync_fs ' > /sys/kernel/debug/tracing/kprobe_events
 # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
 # cat /sys/kernel/debug/trace
            sync-2394  [005]   502.457060: ext4_sync_fs: (ffffffff81317650)
            sync-2394  [005]   502.457063: kernel_stack:         <stack trace>
            sync-2394  [005]   502.457086: ext4_sync_fs: (ffffffff81317650)
            sync-2394  [005]   502.457087: kernel_stack:         <stack trace>
            sync-2394  [005]   502.457091: ext4_sync_fs: (ffffffff81317650)

After putting back the skip stack to zero, we have:

            sync-2270  [000]   748.052693: ext4_sync_fs: (ffffffff81317650)
            sync-2270  [000]   748.052695: kernel_stack:         <stack trace>
 => iterate_supers (ffffffff8126412e)
 => sys_sync (ffffffff8129c4b6)
 => entry_SYSCALL_64_fastpath (ffffffff8181f0b2)
            sync-2270  [000]   748.053017: ext4_sync_fs: (ffffffff81317650)
            sync-2270  [000]   748.053019: kernel_stack:         <stack trace>
 => iterate_supers (ffffffff8126412e)
 => sys_sync (ffffffff8129c4b6)
 => entry_SYSCALL_64_fastpath (ffffffff8181f0b2)
            sync-2270  [000]   748.053381: ext4_sync_fs: (ffffffff81317650)
            sync-2270  [000]   748.053383: kernel_stack:         <stack trace>
 => iterate_supers (ffffffff8126412e)
 => sys_sync (ffffffff8129c4b6)
 => entry_SYSCALL_64_fastpath (ffffffff8181f0b2)

Cc: stable@vger.kernel.org # v4.4+
Fixes: 73dddbb57b "tracing: Only create stacktrace option when STACKTRACE is configured"
Reported-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Tested-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2016-01-13 15:48:54 -05:00 committed by Steven Rostedt
parent afd2ff9b7e
commit 7717c6be69
1 changed files with 1 additions and 1 deletions
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2
kernel/trace/trace.c
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@ -1751,7 +1751,7 @@ void trace_buffer_unlock_commit_regs(struct trace_array *tr,
{
__buffer_unlock_commit(buffer, event);
ftrace_trace_stack(tr, buffer, flags, 6, pc, regs);
ftrace_trace_stack(tr, buffer, flags, 0, pc, regs);
ftrace_trace_userstack(buffer, flags, pc);
}
EXPORT_SYMBOL_GPL(trace_buffer_unlock_commit_regs);