From e1c7e2a6e67fe9db19dd15e71614526a31b5fdb1 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Wed, 24 Jun 2009 09:52:29 +0800 Subject: [PATCH] tracing/events: Don't increment @pos in s_start() While testing syscall tracepoints posted by Jason, I found 3 entries were missing when reading available_events. The output size of available_events is < 4 pages, which means we lost 1 entry per page. The cause is, it's wrong to increment @pos in s_start(). Actually there's another bug here -- reading avaiable_events/set_events can race with module unload: # cat available_events | s_start() | s_stop() | | # rmmod foo.ko s_start() | call = list_entry(m->private) | @call might be freed and accessing it will lead to crash. Reviewed-by: Liming Wang Signed-off-by: Li Zefan Cc: Steven Rostedt Cc: Frederic Weisbecker LKML-Reference: <4A4186DD.6090405@cn.fujitsu.com> Signed-off-by: Ingo Molnar --- kernel/trace/trace_events.c | 28 ++++++++++++++++++++++------ 1 file changed, 22 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index aa08be69a1b6..53c8fd376a88 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -300,10 +300,18 @@ t_next(struct seq_file *m, void *v, loff_t *pos) static void *t_start(struct seq_file *m, loff_t *pos) { + struct ftrace_event_call *call = NULL; + loff_t l; + mutex_lock(&event_mutex); - if (*pos == 0) - m->private = ftrace_events.next; - return t_next(m, NULL, pos); + + m->private = ftrace_events.next; + for (l = 0; l <= *pos; ) { + call = t_next(m, NULL, &l); + if (!call) + break; + } + return call; } static void * @@ -332,10 +340,18 @@ s_next(struct seq_file *m, void *v, loff_t *pos) static void *s_start(struct seq_file *m, loff_t *pos) { + struct ftrace_event_call *call = NULL; + loff_t l; + mutex_lock(&event_mutex); - if (*pos == 0) - m->private = ftrace_events.next; - return s_next(m, NULL, pos); + + m->private = ftrace_events.next; + for (l = 0; l <= *pos; ) { + call = s_next(m, NULL, &l); + if (!call) + break; + } + return call; } static int t_show(struct seq_file *m, void *v)