[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <20200415214033.47e3f95f@oasis.local.home>
Date: Wed, 15 Apr 2020 21:40:33 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Xiao Yang <yangx.jy@...fujitsu.com>
Subject: [GIT PULL] tracing: Fix the race between registering 'snapshot'
event trigger and triggering 'snapshot' operation
Linus,
This fixes a small race between allocating a snapshot buffer and setting the
snapshot trigger. On a slow machine, the trigger can occur before the
snapshot is allocated causing a warning to be displayed in the ring buffer,
and no snapshot triggering. Reversing the allocation and the enabling of the
trigger fixes the problem.
Please pull the latest trace-v5.7-rc1 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v5.7-rc1
Tag SHA1: c27f0128144b8ec3d133d39c81ccdbb53ce811e8
Head SHA1: 0bbe7f719985efd9adb3454679ecef0984cb6800
Xiao Yang (1):
tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation
----
kernel/trace/trace_events_trigger.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
---------------------------
commit 0bbe7f719985efd9adb3454679ecef0984cb6800
Author: Xiao Yang <yangx.jy@...fujitsu.com>
Date: Tue Apr 14 09:51:45 2020 +0800
tracing: Fix the race between registering 'snapshot' event trigger and triggering 'snapshot' operation
Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger()
or snapshot_count_trigger()) when register_snapshot_trigger() has completed
registration but doesn't allocate buffer for 'snapshot' event trigger. In
the rare case, 'snapshot' operation always detects the lack of allocated
buffer so make register_snapshot_trigger() allocate buffer first.
trigger-snapshot.tc in kselftest reproduces the issue on slow vm:
-----------------------------------------------------------
cat trace
...
ftracetest-3028 [002] .... 236.784290: sched_process_fork: comm=ftracetest pid=3028 child_comm=ftracetest child_pid=3036
<...>-2875 [003] .... 240.460335: tracing_snapshot_instance_cond: *** SNAPSHOT NOT ALLOCATED ***
<...>-2875 [003] .... 240.460338: tracing_snapshot_instance_cond: *** stopping trace here! ***
-----------------------------------------------------------
Link: http://lkml.kernel.org/r/20200414015145.66236-1-yangx.jy@cn.fujitsu.com
Cc: stable@...r.kernel.org
Fixes: 93e31ffbf417a ("tracing: Add 'snapshot' event trigger command")
Signed-off-by: Xiao Yang <yangx.jy@...fujitsu.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index dd34a1b46a86..3a74736da363 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1088,14 +1088,10 @@ register_snapshot_trigger(char *glob, struct event_trigger_ops *ops,
struct event_trigger_data *data,
struct trace_event_file *file)
{
- int ret = register_trigger(glob, ops, data, file);
-
- if (ret > 0 && tracing_alloc_snapshot_instance(file->tr) != 0) {
- unregister_trigger(glob, ops, data, file);
- ret = 0;
- }
+ if (tracing_alloc_snapshot_instance(file->tr) != 0)
+ return 0;
- return ret;
+ return register_trigger(glob, ops, data, file);
}
static int
Powered by blists - more mailing lists