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Thu, 25 May 2023 18:51:28 +0000 (UTC) Received: from localhost (unknown [10.39.192.5]) by smtp.corp.redhat.com (Postfix) with ESMTP id 964A7407DEC3; Thu, 25 May 2023 18:51:27 +0000 (UTC) Date: Thu, 25 May 2023 14:51:25 -0400 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-block@nongnu.org, hreitz@redhat.com, eblake@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 06/12] qcow2: Fix open with 'file' in iothread Message-ID: <20230525185125.GH132697@fedora> References: <20230525124713.401149-1-kwolf@redhat.com> <20230525124713.401149-7-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="9KZsKTe07G3aj37j" Content-Disposition: inline In-Reply-To: <20230525124713.401149-7-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org --9KZsKTe07G3aj37j Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, May 25, 2023 at 02:47:07PM +0200, Kevin Wolf wrote: > qcow2_open() doesn't work correctly when opening the 'file' child moves > bs to an iothread, for several reasons: >=20 > - It uses BDRV_POLL_WHILE() to wait for the qcow2_open_entry() > coroutine, which involves dropping the AioContext lock for bs when it > is not in the main context - but we don't hold it, so this crashes. >=20 > - It runs the qcow2_open_entry() coroutine in the current thread instead > of the new AioContext of bs. >=20 > - qcow2_open_entry() doesn't notify the main loop when it's done. >=20 > This patches fixes these issues around delegating work to a coroutine. > Temporarily dropping the main AioContext lock is not necessary because > we know we run in the main thread. >=20 > Signed-off-by: Kevin Wolf > --- > block/qcow2.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) >=20 > diff --git a/block/qcow2.c b/block/qcow2.c > index b00b4e7575..7f3948360d 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -1904,6 +1904,8 @@ static void coroutine_fn qcow2_open_entry(void *opa= que) > qoc->ret =3D qcow2_do_open(qoc->bs, qoc->options, qoc->flags, true, > qoc->errp); > qemu_co_mutex_unlock(&s->lock); > + > + aio_wait_kick(); > } > =20 > static int qcow2_open(BlockDriverState *bs, QDict *options, int flags, > @@ -1929,8 +1931,10 @@ static int qcow2_open(BlockDriverState *bs, QDict = *options, int flags, > =20 > assert(!qemu_in_coroutine()); > assert(qemu_get_current_aio_context() =3D=3D qemu_get_aio_context()); > - qemu_coroutine_enter(qemu_coroutine_create(qcow2_open_entry, &qoc)); > - BDRV_POLL_WHILE(bs, qoc.ret =3D=3D -EINPROGRESS); > + > + aio_co_enter(bdrv_get_aio_context(bs), > + qemu_coroutine_create(qcow2_open_entry, &qoc)); > + AIO_WAIT_WHILE_UNLOCKED(NULL, qoc.ret =3D=3D -EINPROGRESS); Want to update the doc comment for bdrv_open_file_child() with a warning that @parent's AioContext can change? Otherwise: Reviewed-by: Stefan Hajnoczi --9KZsKTe07G3aj37j Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmRvri0ACgkQnKSrs4Gr c8iPUAf+PddWdSru0kM1p1MsBZe9h3G4NtSmpOsIS1oJto0IFdGEqwdwsSm1NrtJ Ukp78rxLMBtzXH/E2ZZfeFFhFnvv8Yh50kCaJW/uHOhpmnAd9uQ0eJ3FS5c1xVA+ GsYcCxs5BT1qlC9HW3AqDAm3VA12/39CuXXKUIfTMOLCF2/DRxUUZgFP3P8HaHSA tL6IXj93k1fOHoCOV5aqH8REsdKR8bu6veM/bcaBeEyHyTfN0hHBB5JavObZnnPF lElZro+7TYSkjJ89/rZT0b2J61ISOVcd2mvswTpI9aIOp6Q8kO0wlRoA/RULZ3j2 Qtq0/kt8LSiNrN0DLSyAqvsh7QkuJQ== =zRfm -----END PGP SIGNATURE----- --9KZsKTe07G3aj37j--