Re: [PATCH v5 3/3] tty: fix data race on tty_buffer.commit

[Peter Hurley]

On Thu, Sep 17, 2015 at 11:17 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Race on buffer data happens when newly committed data is
> picked up by an old flush work in the following scenario:
> __tty_buffer_request_room does a plain write of tail->commit,
> no barriers were executed before that.
> At this point flush_to_ldisc reads this new value of commit,
> and reads buffer data, no barriers in between.
> The committed buffer data is not necessary visible to flush_to_ldisc.
>
> Similar bug happens when tty_schedule_flip commits data.
>
> Update commit with smp_store_release and read commit with
> smp_load_acquire, as it is commit that signals data readiness.
> This is orthogonal to the existing synchronization on tty_buffer.next,
> which is required to not dismiss a buffer with unconsumed data.
>
> The data race was found with KernelThreadSanitizer (KTSAN).

Reviewed-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
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