linux-kernel - Re: [PATCH] perf/core: Fix reversed NULL check in perf_event_groups

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Date:   Fri, 13 Mar 2020 13:27:25 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Ian Rogers <irogers@...gle.com>, 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>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] perf/core: Fix reversed NULL check in
 perf_event_groups_less()

On Thu, Mar 12, 2020 at 01:56:37PM +0300, Dan Carpenter wrote:
> This NULL check is reversed so it leads to a Smatch warning and
> presumably a NULL dereference.
> 
>     kernel/events/core.c:1598 perf_event_groups_less()
>     error: we previously assumed 'right->cgrp->css.cgroup' could be null
> 	(see line 1590)
> 
> Fixes: 95ed6c707f26 ("perf/cgroup: Order events in RB tree by cgroup id")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 6a47c3e54fe9..607c04ec7cfa 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1587,7 +1587,7 @@ perf_event_groups_less(struct perf_event *left, struct perf_event *right)
>  			 */
>  			return true;
>  		}
> -		if (!right->cgrp || right->cgrp->css.cgroup) {
> +		if (!right->cgrp || !right->cgrp->css.cgroup) {
>  			/*
>  			 * Right has no cgroup but left does, no cgroups come
>  			 * first.

Thanks!