| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 016/117] tracing: Fix stacktrace skip depth in trace_buffer_unlock_commit_regs() | Date | Sun, 14 Feb 2016 14:20:53 -0800 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>
commit 7717c6be699975f6733d278b13b7c4295d73caf6 upstream.
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)
Fixes: 73dddbb57bb0 "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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1751,7 +1751,7 @@ void trace_buffer_unlock_commit_regs(str { __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);
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