Messages in this thread Patch in this message | | | Date | Fri, 19 Jun 2009 14:45:41 +0800 | From | Li Zefan <> | Subject | [PATCH 1/5] tracing/events: don't increment @pos in s_start() |
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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 item 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.
[ Impact fix missing entries when reading available_events/set_events ]
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> --- kernel/trace/trace_events.c | 28 ++++++++++++++++++++++------ 1 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index aa341ff..4ab596e 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) -- 1.5.4.rc3
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