From 7717c6be699975f6733d278b13b7c4295d73caf6 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Wed, 13 Jan 2016 15:48:54 -0500 Subject: [PATCH] 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: sync-2394 [005] 502.457086: ext4_sync_fs: (ffffffff81317650) sync-2394 [005] 502.457087: kernel_stack: 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: => 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: => 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: => iterate_supers (ffffffff8126412e) => sys_sync (ffffffff8129c4b6) => entry_SYSCALL_64_fastpath (ffffffff8181f0b2) Cc: stable@vger.kernel.org # v4.4+ Fixes: 73dddbb57bb0 "tracing: Only create stacktrace option when STACKTRACE is configured" Reported-by: Brendan Gregg Tested-by: Brendan Gregg Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 87fb9801bd9e..d9293402ee68 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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); -- 2.20.1