linux-kernel - Re: [PATCH] perf: Fix sys_perf_event

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Message-ID: <Y3Vkmvi2vib7fwHn@zn.tnic>
Date:   Wed, 16 Nov 2022 23:30:50 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>, nslusarek@....net,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Fix sys_perf_event_open() race against self

On Mon, May 23, 2022 at 04:03:29PM +0530, Ravi Bangoria wrote:
> On 21-May-22 12:08 AM, Peter Zijlstra wrote:
> > 
> > Norbert reported that it's possible to race sys_perf_event_open() such
> > that the looser ends up in another context from the group leader,
> > triggering many WARNs.
> > 
> > The move_group case checks for races against itself, but the
> > !move_group case doesn't, seemingly relying on the previous
> > group_leader->ctx == ctx check. However, that check is racy due to not
> > holding any locks at that time.
> > 
> > Therefore, re-check the result after acquiring locks and bailing
> > if they no longer match.
> > 
> > Additionally, clarify the not_move_group case from the
> > move_group-vs-move_group race.
> 
> Tested-by: Ravi Bangoria <ravi.bangoria@....com>
> 
> Below is a quick test to reproduce the issue. It triggers WARN_ON()
> as normal user. No warnings with the patch.

Shouldn't this test be in tools/perf/tests/ or so?

If that hasn't happened yet, I mean.

Thx.

-- 
Regards/Gruss,
    Boris.

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