From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Roman Kagan <rvkagan@yandex-team.ru>, qemu-devel@nongnu.org
Cc: yc-core@yandex-team.ru, Eric Blake <eblake@redhat.com>,
Max Reitz <mreitz@redhat.com>, Kevin Wolf <kwolf@redhat.com>,
qemu-block@nongnu.org
Subject: Re: [PATCH 1/7] block/nbd: avoid touching freed connect_thread
Date: Mon, 15 Mar 2021 18:40:12 +0300 [thread overview]
Message-ID: <b551f5f1-fc80-db3c-57a8-627195048bf4@virtuozzo.com> (raw)
In-Reply-To: <20210315060611.2989049-2-rvkagan@yandex-team.ru>
15.03.2021 09:06, Roman Kagan wrote:
> When the NBD connection is being torn down, the connection thread gets
> canceled and "detached", meaning it is about to get freed.
>
> If this happens while the connection coroutine yielded waiting for the
> connection thread to complete, when it resumes it may access the
> invalidated connection thread data.
>
> To prevent this, revalidate the ->connect_thread pointer in
> nbd_co_establish_connection_cancel before using after the the yield.
>
> Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
Seems possible. Do you have a reproducer? Would be great to make an iotest.
> ---
> block/nbd.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/block/nbd.c b/block/nbd.c
> index c26dc5a54f..447d176b76 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -486,6 +486,15 @@ nbd_co_establish_connection(BlockDriverState *bs, Error **errp)
> s->wait_connect = true;
> qemu_coroutine_yield();
>
> + /*
> + * If nbd_co_establish_connection_cancel had a chance to run it may have
> + * invalidated ->connect_thread.
> + */
> + thr = s->connect_thread;
> + if (!thr) {
> + return -ECONNABORTED;
> + }
> +
> qemu_mutex_lock(&thr->mutex);
>
> switch (thr->state) {
>
Patch looks a bit like s->connect_thread may become something other than NULL during the yield.. But it can't actually. Maybe it will be possible with further patches?
Anyway, make sense to me:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
--
Best regards,
Vladimir
next prev parent reply other threads:[~2021-03-15 15:43 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 6:06 [PATCH 0/7] block/nbd: decouple reconnect from drain Roman Kagan
2021-03-15 6:06 ` [PATCH 1/7] block/nbd: avoid touching freed connect_thread Roman Kagan
2021-03-15 15:40 ` Vladimir Sementsov-Ogievskiy [this message]
2021-03-16 15:29 ` Roman Kagan
2021-04-06 16:21 ` Vladimir Sementsov-Ogievskiy
2021-03-15 6:06 ` [PATCH 2/7] block/nbd: use uniformly nbd_client_connecting_wait Roman Kagan
2021-03-15 15:48 ` Vladimir Sementsov-Ogievskiy
2021-03-15 6:06 ` [PATCH 3/7] block/nbd: assert attach/detach runs in the proper context Roman Kagan
2021-03-15 16:41 ` Vladimir Sementsov-Ogievskiy
2021-03-15 19:57 ` Roman Kagan
2021-03-15 6:06 ` [PATCH 4/7] block/nbd: transfer reconnection stuff across aio_context switch Roman Kagan
2021-03-15 6:06 ` [PATCH 5/7] block/nbd: better document a case in nbd_co_establish_connection Roman Kagan
2021-03-15 6:06 ` [PATCH 6/7] block/nbd: decouple reconnect from drain Roman Kagan
2021-03-15 20:10 ` Vladimir Sementsov-Ogievskiy
2021-03-16 16:03 ` Roman Kagan
2021-03-16 18:09 ` Vladimir Sementsov-Ogievskiy
2021-03-26 6:16 ` Roman Kagan
2021-03-15 6:06 ` [PATCH 7/7] block/nbd: stop manipulating in_flight counter Roman Kagan
2021-03-15 20:15 ` Vladimir Sementsov-Ogievskiy
2021-03-16 16:08 ` Roman Kagan
2021-03-16 18:37 ` Vladimir Sementsov-Ogievskiy
2021-03-26 7:41 ` Roman Kagan
2021-03-15 19:45 ` [PATCH 0/7] block/nbd: decouple reconnect from drain Vladimir Sementsov-Ogievskiy
2021-03-16 15:52 ` Roman Kagan
2021-03-16 14:41 ` Eric Blake
2021-03-16 16:10 ` Roman Kagan
2021-03-17 8:35 ` Vladimir Sementsov-Ogievskiy
2021-03-26 8:07 ` Roman Kagan
2021-04-07 7:45 ` Roman Kagan
2021-04-07 10:13 ` Vladimir Sementsov-Ogievskiy
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