linux-kernel - Re: [PATCH v6] taskstats: fix data-race

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Message-ID: <20191129175752.GB29789@willie-the-truck>
Date:   Fri, 29 Nov 2019 17:57:53 +0000
From:   Will Deacon <will@...nel.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org, bsingharora@...il.com,
        dvyukov@...gle.com, elver@...gle.com, parri.andrea@...il.com,
        stable@...r.kernel.org,
        syzbot+c5d03165a1bd1dead0c1@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v6] taskstats: fix data-race

On Mon, Oct 21, 2019 at 01:33:27PM +0200, Christian Brauner wrote:
> When assiging and testing taskstats in taskstats_exit() there's a race
> when writing and reading sig->stats when a thread-group with more than
> one thread exits:
> 
> cpu0:
> thread catches fatal signal and whole thread-group gets taken down
>  do_exit()
>  do_group_exit()

Nit: I don't think this is the signal-handling path.

>  taskstats_exit()
>  taskstats_tgid_alloc()
> The tasks reads sig->stats without holding sighand lock.
> 
> cpu1:
> task calls exit_group()
>  do_exit()
>  do_group_exit()

Nit: These ^^ seem to be the wrong way round.

Will