linux-kernel - Re: [PATCH 1/2] tracing: Check total refcount before releasing bufs in profile

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Date:	Wed, 7 Oct 2009 14:08:27 +1100
From:	Paul Mackerras <paulus@...ba.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Li Zefan <lizf@...fujitsu.com>
Subject: Re: [PATCH 1/2] tracing: Check total refcount before releasing bufs in profile_enable failure

Frederic Weisbecker writes:

> When we call the profile_enable() callback of an event, we release the
> shared perf event tracing buffers unconditionnaly in the failure path.
> This is wrong because there may be other users of these. Then check the
> total refcount before doing this.

[snip]

> -	kfree(trace_profile_buf_nmi);
>  fail_buf_nmi:
> -	kfree(trace_profile_buf);
> +	if (!total_profile_count) {

A small problem here: total_profile_count will be 1, not 0, in the
case where we need to free...

> +		kfree(trace_profile_buf_nmi);
> +		kfree(trace_profile_buf);
> +		trace_profile_buf_nmi = NULL;
> +		trace_profile_buf = NULL;
> +	}
>  fail_buf:
> -	total_profile_count--;

since we don't decrement total_profile_count until here.

Paul.
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