tracing: Fix preempt count leak

While running my ftrace stress test, this showed up:

BUG: sleeping function called from invalid context at mm/mmap.c:233
...
note: cat[3293] exited with preempt_count 1

The bug was introduced by commit 91e86e560d0b3ce4c5fc64fd2bbb99f856a30a4e
("tracing: Fix recursive user stack trace")

Cc: <stable@kernel.org>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
LKML-Reference: <4D0089AC.1020802@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 2 insertions, 4 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f8cf959bad4..dc53ecb8058 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1313,12 +1313,10 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
 
         __this_cpu_inc(user_stack_count);
 
-
-
         event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK,
                                           sizeof(*entry), flags, pc);
         if (!event)
-                return;
+                goto out_drop_count;
         entry   = ring_buffer_event_data(event);
 
         entry->tgid             = current->tgid;
@@ -1333,8 +1331,8 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
         if (!filter_check_discard(call, entry, buffer, event))
                 ring_buffer_unlock_commit(buffer, event);
 
+ out_drop_count:
         __this_cpu_dec(user_stack_count);
-
  out:
         preempt_enable();
 }