From: Mike Snitzer <snitzer@redhat.com>
To: NeilBrown <neilb@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org,
device-mapper development <dm-devel@redhat.com>,
Milan Broz <gmazyland@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: block: be more careful about status in __bio_chain_endio
Date: Fri, 22 Feb 2019 16:10:06 -0500 [thread overview]
Message-ID: <20190222211006.GA10987@redhat.com> (raw)
In-Reply-To: <87eflmpqkb.fsf@notabene.neil.brown.name>
On Thu, Feb 15 2018 at 4:09am -0500,
NeilBrown <neilb@suse.com> wrote:
>
> If two bios are chained under the one parent (with bio_chain())
> it is possible that one will succeed and the other will fail.
> __bio_chain_endio must ensure that the failure error status
> is reported for the whole, rather than the success.
>
> It currently tries to be careful, but this test is racy.
> If both children finish at the same time, they might both see that
> parent->bi_status as zero, and so will assign their own status.
> If the assignment to parent->bi_status by the successful bio happens
> last, the error status will be lost which can lead to silent data
> corruption.
>
> Instead, __bio_chain_endio should only assign a non-zero status
> to parent->bi_status. There is then no need to test the current
> value of parent->bi_status - a test that would be racy anyway.
>
> Note that this bug hasn't been seen in practice. It was only discovered
> by examination after a similar bug was found in dm.c
>
> Signed-off-by: NeilBrown <neilb@suse.com>
> ---
> block/bio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index e1708db48258..ad77140edc6f 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -312,7 +312,7 @@ static struct bio *__bio_chain_endio(struct bio *bio)
> {
> struct bio *parent = bio->bi_private;
>
> - if (!parent->bi_status)
> + if (bio->bi_status)
> parent->bi_status = bio->bi_status;
> bio_put(bio);
> return parent;
> --
> 2.14.0.rc0.dirty
>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Jens, this one slipped through the crack just over a year ago.
It is available in patchwork here:
https://patchwork.kernel.org/patch/10220727/
next parent reply other threads:[~2019-02-22 21:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <70cda2a3-f246-d45b-f600-1f9d15ba22ff@gmail.com>
[not found] ` <87eflmpqkb.fsf@notabene.neil.brown.name>
2019-02-22 21:10 ` Mike Snitzer [this message]
2019-02-22 22:46 ` block: be more careful about status in __bio_chain_endio Jens Axboe
2019-02-22 23:55 ` Mike Snitzer
2019-02-23 2:02 ` John Dorminy
2019-02-23 2:44 ` Mike Snitzer
2019-02-23 3:10 ` John Dorminy
2019-06-12 2:56 ` John Dorminy
2019-06-12 7:01 ` Christoph Hellwig
2019-06-17 7:32 ` Hannes Reinecke
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