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trigger_next should increase position index 

[ Upstream commit 6722b23e7a ]

if seq_file .next fuction does not change position index,
read after some lseek can generate unexpected output.

Without patch:
 # dd bs=30 skip=1 if=/sys/kernel/tracing/events/sched/sched_switch/trigger
 dd: /sys/kernel/tracing/events/sched/sched_switch/trigger: cannot skip to specified offset
 n traceoff snapshot stacktrace enable_event disable_event enable_hist disable_hist hist
 # Available triggers:
 # traceon traceoff snapshot stacktrace enable_event disable_event enable_hist disable_hist hist
 6+1 records in
 6+1 records out
 206 bytes copied, 0.00027916 s, 738 kB/s

Notice the printing of "# Available triggers:..." after the line.

With the patch:
 # dd bs=30 skip=1 if=/sys/kernel/tracing/events/sched/sched_switch/trigger
 dd: /sys/kernel/tracing/events/sched/sched_switch/trigger: cannot skip to specified offset
 n traceoff snapshot stacktrace enable_event disable_event enable_hist disable_hist hist
 2+1 records in
 2+1 records out
 88 bytes copied, 0.000526867 s, 167 kB/s

It only prints the end of the file, and does not restart.

Link: http://lkml.kernel.org/r/3c35ee24-dd3a-8119-9c19-552ed253388a@virtuozzo.com

https://bugzilla.kernel.org/show_bug.cgi?id=206283
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
5.4-rM2-2.2.x-imx-squashed
Vasily Averin 2020-01-24 10:03:06 +03:00 committed by Greg Kroah-Hartman
parent e349287276
commit 224c0751df
1 changed files with 3 additions and 2 deletions
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5
kernel/trace/trace_events_trigger.c
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@ -116,9 +116,10 @@ static void *trigger_next(struct seq_file *m, void *t, loff_t *pos)
{
struct trace_event_file *event_file = event_file_data(m->private);
if (t == SHOW_AVAILABLE_TRIGGERS)
if (t == SHOW_AVAILABLE_TRIGGERS) {
(*pos)++;
return NULL;
}
return seq_list_next(t, &event_file->triggers, pos);
}