linux-kernel - Re: [PATCH] tracing/perf: Fix double put of trace event when init fails

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Date:   Wed, 17 Aug 2022 10:03:31 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Krister Johansen <kjlx@...pleofstupid.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        David Reaver <me@...idreaver.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH] tracing/perf: Fix double put of trace event when init
 fails

On Tue, 16 Aug 2022 21:46:56 -0700
Krister Johansen <kjlx@...pleofstupid.com> wrote:

> Thanks again, Steven.  Is this one that you would consider tagging for a
> backport to stable at the appropriate time? I believe this one showed up
> in 5.15, if it's any help.

So the warning started with this commit:

   1d18538e6a092 ("tracing: Have dynamic events have a ref counter")

Which switched the module_put() to the trace_event_put(). I guess the
difference is that module_put() has

	ret = atomic_dec_if_positive(&module->refcnt);

Where it could be called more than once after reaching zero and not warn
about it. But the trace_event_put() will warn if you call it after it
reaches zero.

I'll add a stable tag.

-- Steve