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SubjectRe: [PATCH] tracing/perf: Fix double put of trace event when init fails
On Tue, Aug 16, 2022 at 07:28:17PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
>
> If in perf_trace_event_init(), the perf_trace_event_open() fails, then it
> will call perf_trace_event_unreg() which will not only unregister the perf
> trace event, but will also call the put() function of the tp_event.
>
> The problem here is that the trace_event_try_get_ref() is called by the
> caller of perf_trace_event_init() and if perf_trace_event_init() returns a
> failure, it will then call trace_event_put(). But since the
> perf_trace_event_unreg() already called the trace_event_put() function, it
> triggers a WARN_ON().
>
> WARNING: CPU: 1 PID: 30309 at kernel/trace/trace_dynevent.c:46 trace_event_dyn_put_ref+0x15/0x20
>
> If perf_trace_event_reg() does not call the trace_event_try_get_ref() then
> the perf_trace_event_unreg() should not be calling trace_event_put(). This
> breaks symmetry and causes bugs like these.
>
> Pull out the trace_event_put() from perf_trace_event_unreg() and call it
> in the locations that perf_trace_event_unreg() is called. This not only
> fixes this bug, but also brings back the proper symmetry of the reg/unreg
> vs get/put logic.
>
> Link: https://lore.kernel.org/all/cover.1660347763.git.kjlx@templeofstupid.com/
>
> Reported-by: Krister Johansen <kjlx@templeofstupid.com>
> Reviewed-by: Krister Johansen <kjlx@templeofstupid.com>
> Tested-by: Krister Johansen <kjlx@templeofstupid.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

LGTM

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
> kernel/trace/trace_event_perf.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index a114549720d6..61e3a2620fa3 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -157,7 +157,7 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
> int i;
>
> if (--tp_event->perf_refcount > 0)
> - goto out;
> + return;
>
> tp_event->class->reg(tp_event, TRACE_REG_PERF_UNREGISTER, NULL);
>
> @@ -176,8 +176,6 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
> perf_trace_buf[i] = NULL;
> }
> }
> -out:
> - trace_event_put_ref(tp_event);
> }
>
> static int perf_trace_event_open(struct perf_event *p_event)
> @@ -241,6 +239,7 @@ void perf_trace_destroy(struct perf_event *p_event)
> mutex_lock(&event_mutex);
> perf_trace_event_close(p_event);
> perf_trace_event_unreg(p_event);
> + trace_event_put_ref(p_event->tp_event);
> mutex_unlock(&event_mutex);
> }
>
> @@ -292,6 +291,7 @@ void perf_kprobe_destroy(struct perf_event *p_event)
> mutex_lock(&event_mutex);
> perf_trace_event_close(p_event);
> perf_trace_event_unreg(p_event);
> + trace_event_put_ref(p_event->tp_event);
> mutex_unlock(&event_mutex);
>
> destroy_local_trace_kprobe(p_event->tp_event);
> @@ -347,6 +347,7 @@ void perf_uprobe_destroy(struct perf_event *p_event)
> mutex_lock(&event_mutex);
> perf_trace_event_close(p_event);
> perf_trace_event_unreg(p_event);
> + trace_event_put_ref(p_event->tp_event);
> mutex_unlock(&event_mutex);
> destroy_local_trace_uprobe(p_event->tp_event);
> }
> --
> 2.35.1
>

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