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

From: Peter Hurley
Date: Thu Sep 17 2015 - 13:42:15 EST


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>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/