linux-kernel - Re: [PATCH] events: Reuse value read using READ

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Message-ID: <20210910162107.GK4323@worktop.programming.kicks-ass.net>
Date:   Fri, 10 Sep 2021 18:21:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Baptiste Lepers <baptiste.lepers@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] events: Reuse value read using READ_ONCE instead of
 re-reading it

On Mon, Sep 06, 2021 at 11:53:10AM +1000, Baptiste Lepers wrote:
> In perf_event_addr_filters_apply, the task associated with
> the event (event->ctx->task) is read using READ_ONCE at the beginning
> of the function, checked, and then re-read from event->ctx->task,
> voiding all guarantees of the checks. Reuse the value that was read by
> READ_ONCE to ensure the consistency of the task struct throughout the
> function.
> 
> Signed-off-by: Baptiste Lepers <baptiste.lepers@...il.com>
> Fixes: 375637bc52495 ("perf/core: Introduce address range filtering")

Thanks!