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Fri, 13 Sep 2019 11:48:37 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-116-81.ams2.redhat.com [10.36.116.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D9049600CE; Fri, 13 Sep 2019 11:48:32 +0000 (UTC) To: qemu-block@nongnu.org References: <20190910124136.10565-1-mreitz@redhat.com> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <9029d621-0b48-9a65-5699-7c55151e6b81@redhat.com> Date: Fri, 13 Sep 2019 13:48:31 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190910124136.10565-1-mreitz@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="MGGTposjemt39S0EnSri9tK0Odgi1DG70" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 13 Sep 2019 11:48:37 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 0/7] block/curl: Fix hang and potential crash X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , John Snow , qemu-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --MGGTposjemt39S0EnSri9tK0Odgi1DG70 Content-Type: multipart/mixed; boundary="dEJ6YMG357DKtGuMaNsZEEoddL3hM1Mwx"; protected-headers="v1" From: Max Reitz To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, John Snow , Kevin Wolf , qemu-stable@nongnu.org Message-ID: <9029d621-0b48-9a65-5699-7c55151e6b81@redhat.com> Subject: Re: [PATCH v2 0/7] block/curl: Fix hang and potential crash References: <20190910124136.10565-1-mreitz@redhat.com> In-Reply-To: <20190910124136.10565-1-mreitz@redhat.com> --dEJ6YMG357DKtGuMaNsZEEoddL3hM1Mwx Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 10.09.19 14:41, Max Reitz wrote: > Hi, >=20 > As reported in https://bugzilla.redhat.com/show_bug.cgi?id=3D1740193, o= ur > curl block driver can spontaneously hang. This becomes visible e.g. > when reading compressed qcow2 images: >=20 > $ qemu-img convert -p -O raw -n \ > https://download.cirros-cloud.net/0.4.0/cirros-0.4.0-x86_64-disk.img = \ > null-co:// >=20 > (Hangs at 74.21 %, usually.) >=20 > A more direct way is: >=20 > $ qemu-img bench -f raw http://download.qemu.org/qemu-4.1.0.tar.xz \ > -d 1 -S 524288 -c 2 >=20 > (Which simply performs two requests, and the second one hangs. You can= > use any HTTP resource (probably FTP, too) you=E2=80=99d like that is at= least > 1 MB in size.) >=20 > It turns out that this is because cURL 7.59.0 has added a protective > feature against some misuse we had in our code: curl_multi_add_handle()= > must not be called from within a cURL callback, but in some cases we > did. As of 7.59.0, this fails, our new request is not registered and > the I/O request stalls. This is fixed by patch 6. >=20 > Patch 7 makes us check for curl_multi_add_handle()=E2=80=99s return cod= e, > because if we had done that before, debugging would have been much > simpler. >=20 >=20 > On the way to fixing it, I had a look over the whole cURL code and foun= d > a suspicious QLIST_FOREACH_SAFE() loop that actually does not seem very= > safe at all. I think this may lead to crashes, although I have never > seen any myself. https://bugzilla.redhat.com/show_bug.cgi?id=3D1744602= #c5 > shows one in exactly the function in question, so I think it actually i= s > a problem. >=20 > This is fixed by patch 5, patches 1, 2, and 4 prepare for it. >=20 > (Patch 3 is kind of a misc patch that should ensure that we always end > up calling curl_multi_check_completion() whenever a request might have > been completed.) Thanks for the review, applied to my block branch: https://git.xanclic.moe/XanClic/qemu/commits/branch/block Max --dEJ6YMG357DKtGuMaNsZEEoddL3hM1Mwx-- --MGGTposjemt39S0EnSri9tK0Odgi1DG70 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl17gg8ACgkQ9AfbAGHV z0A6iAf+OWuzCyaWNXk0mrwFwcwfRefl76baF5j7yqlWfV9nz96y5ZP41khBDWL7 1eGebNGaO2vdM3pzFBP0Ps590C8/tyNhPs5bFP6k6QQ5EPs+vHgAngv8Znev2MTO 20Wku6Io5AWSABM/uiQ9VpC+f1rrLkZJf6fGQf3SskFqtOWSWPfTRzWIbErSw1ZM g0+Pyi93QfyFtDu8/SD9evGVyEws0ELaQZu2hbmthilvURlvYzA7+zKKGh04osjY 7/jvZViKA32YNG8M+FR0gyi8eMXH/1eBW8y652goYB3VEEYWNgULR+5s7iPAV85E WZQCPWYbrL46UmbRuMKavJwAdYM1DA== =h9u1 -----END PGP SIGNATURE----- --MGGTposjemt39S0EnSri9tK0Odgi1DG70--