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Fri, 15 Feb 2019 10:58:32 +0100 Subject: Re: [PATCH v4 04/12] btrfs: extent_io: Move the BUG_ON() in flush_write_bio() one level up From: Qu Wenruo To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org References: <20190125050925.30754-1-wqu@suse.com> <20190125050925.30754-5-wqu@suse.com> <20190130151914.GU2900@twin.jikos.cz> <3893155e-d3c3-5fd0-6f61-ae067d341d81@gmx.com> <20190131143637.GF2900@twin.jikos.cz> Openpgp: preference=signencrypt Autocrypt: addr=quwenruo.btrfs@gmx.com; prefer-encrypt=mutual; keydata= mQENBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAG0IlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT6JAVQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWCnQUJCWYC bgAKCRDCPZHzoSX+qAR8B/94VAsSNygx1C6dhb1u1Wp1Jr/lfO7QIOK/nf1PF0VpYjTQ2au8 ihf/RApTna31sVjBx3jzlmpy+lDoPdXwbI3Czx1PwDbdhAAjdRbvBmwM6cUWyqD+zjVm4RTG rFTPi3E7828YJ71Vpda2qghOYdnC45xCcjmHh8FwReLzsV2A6FtXsvd87bq6Iw2axOHVUax2 FGSbardMsHrya1dC2jF2R6n0uxaIc1bWGweYsq0LXvLcvjWH+zDgzYCUB0cfb+6Ib/ipSCYp 3i8BevMsTs62MOBmKz7til6Zdz0kkqDdSNOq8LgWGLOwUTqBh71+lqN2XBpTDu1eLZaNbxSI ilaVuQENBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAGJATwEGAEIACYWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCWdWBrwIbDAUJA8JnAAAK CRDCPZHzoSX+qA3xB/4zS8zYh3Cbm3FllKz7+RKBw/ETBibFSKedQkbJzRlZhBc+XRwF61mi f0SXSdqKMbM1a98fEg8H5kV6GTo62BzvynVrf/FyT+zWbIVEuuZttMk2gWLIvbmWNyrQnzPl mnjK4AEvZGIt1pk+3+N/CMEfAZH5Aqnp0PaoytRZ/1vtMXNgMxlfNnb96giC3KMR6U0E+siA 4V7biIoyNoaN33t8m5FwEwd2FQDG9dAXWhG13zcm9gnk63BN3wyCQR+X5+jsfBaS4dvNzvQv h8Uq/YGjCoV1ofKYh3WKMY8avjq25nlrhzD/Nto9jHp8niwr21K//pXVA81R2qaXqGbql+zo Message-ID: <58b95afa-d627-6aa8-17a3-8e19d7eccafe@gmx.com> Date: Fri, 15 Feb 2019 17:58:26 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="1vcLowf7xC0353BwxDhbzmkOT71jGxwAi" X-Provags-ID: V03:K1:xxok3AY6RmkCnQ5VZdN7h6rifQCCaQ2f7TZDcyCavCVxiER8FJB yc33loXhCDPNNsCpuQpPTxYcqKKWhbYOsyqlb4OQHZopI+TgmwH9Itb5f/dOJCCyJrQkJWC ymP+2pgQl/7OgfGZEcAuFU1SV0oiy8mpONaHRjbadE3KoqakQDl2+svEUL1pRAadHgOMi7f zTKvJGpfya0IMfFQxiraw== X-UI-Out-Filterresults: notjunk:1;V03:K0:EKfgFSCp0q4=:XyVIKBk60Hpx0KsSdMfU2q kRelaFHHYYaya+2kW7IZrGwn5+CC35/Jo2BQ3W0nENpZnmJcFEYCOb4MCaHZuTcdHfkGuLAKb 79Sn3W08s4O50nbtlYf0fpNRuDSn31s3Gjxv4K2vVWFwgK48NGzB7Sr/95tV4OhnOS6ESTAdf KY7Ui7iXCymaqZc6rZzCmfiEDMx5qO60dILH8bg8Uj6m2jaXu0oZE8qPzQYQcOgVYAQgo2q1P VvCNC9rwraSXGb9AweQ4DXoAB7JrzI47PU6BuBF8G26fC/tfQ+izvQ/O9uBkk5HKGpqu2Z7Ex BJ35co5aJuNtmTqox3h1zEn0uc3FAphnJzkNGETgGv9LDKLaVad3CrDHni2gu12LBIeM3LnOl IKLTzB5kuOp0W/nwkHSNeKN7sDMj325plp909HR86aq2z7VhlvjIOcZhvW2YI9kLEPrDrRzQ+ BlUZZpTURjzWJUB+4UGOlbYHOZS9MfXdjACg+4DrvoHWSO2bn04ovSsNOxAYWHk/a0SGmfeQT kuwtA3eoMOEKUMOzFHN57iaZuVcZmzLTMLCevePJC6XBDum2r0b+IPHDoROU1fTAhr8dWiu/x X2VYrPEGo8X992nJCq+gYrivfBwRyMaEQUC9zMtcOjtn+o0KKMxPfiBHXbbbVRelQSPM6uHZJ u2WvU2VH7RjT9cj/XCMxJ0bZ0SDd6A2AaNtuSaIC/VAZNhSERi63xTwITTQixooJt2sjY0rzl 9xuSQBqToxjDtwKeePDAtFEZiWJJLDdGCrN1YD9ePWO2VVMcjIWES+/yXm7c6e5OlNDPKOAh4 y2mnTYFh0aQ6MIKl6gSg7FBfHp8kL0htX1mGz+gy+D02nrChOgEhJ0cJXyCg/iOBdFY5mcz+U HbGEwwYWs33KhlYaOPNTKGBythADgqV5b6mHMrcQqRry2Y56h0BUth5cTQZGFG Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --1vcLowf7xC0353BwxDhbzmkOT71jGxwAi Content-Type: multipart/mixed; boundary="RPPaDlEQNLRQFmKwfDEfqDxXwqU6nNcMP"; protected-headers="v1" From: Qu Wenruo To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org Message-ID: <58b95afa-d627-6aa8-17a3-8e19d7eccafe@gmx.com> Subject: Re: [PATCH v4 04/12] btrfs: extent_io: Move the BUG_ON() in flush_write_bio() one level up References: <20190125050925.30754-1-wqu@suse.com> <20190125050925.30754-5-wqu@suse.com> <20190130151914.GU2900@twin.jikos.cz> <3893155e-d3c3-5fd0-6f61-ae067d341d81@gmx.com> <20190131143637.GF2900@twin.jikos.cz> In-Reply-To: --RPPaDlEQNLRQFmKwfDEfqDxXwqU6nNcMP Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2019/2/15 =E4=B8=8B=E5=8D=883:18, Qu Wenruo wrote: >=20 >=20 > On 2019/1/31 =E4=B8=8B=E5=8D=8810:36, David Sterba wrote: >> On Thu, Jan 31, 2019 at 08:45:42AM +0800, Qu Wenruo wrote: >>> >>> >>> On 2019/1/30 =E4=B8=8B=E5=8D=8811:19, David Sterba wrote: >>>> On Fri, Jan 25, 2019 at 01:09:17PM +0800, Qu Wenruo wrote: >>>>> +static int __must_check flush_write_bio(struct extent_page_data *e= pd) >>>>> { >>>>> - if (epd->bio) { >>>>> - int ret; >>>>> + int ret =3D 0; >>>>> =20 >>>>> + if (epd->bio) { >>>>> ret =3D submit_one_bio(epd->bio, 0, 0); >>>>> - BUG_ON(ret < 0); /* -ENOMEM */ >>>>> epd->bio =3D NULL; >>>> >>>> I'm not sure if resetting epd->bio to NULL is all that needs to be d= one >>>> here. With the BUG_ON the error case never happens so if all goes fi= ne >>>> it's also ok to set it to NULL and continue. But the callers might n= eed >>>> to send the flush again. >>> >>> If flush_write_bio() get called again on the failed one, it will just= >>> get skipped as epd->bio is NULL, submit_one_bio() will not be trigge= red. >> >> Yes that's clear, but what is the state of the bio that went to >> flush_write_bio and submit_one_bio failed? >> >=20 > You got me. >=20 > In fact current simple "epd->bio =3D NULL" on failure will just leak ep= d->bio. >=20 > We need to at least call "bio_put(epd->bio);" before setting "epd->bio = =3D > NULL;" Facepalm, I'm always too quick to draw a conclusion. With proper test, the epd->bio is freed by its endio function. So at flush_write_bio() call time, no matter whether submit_one_bio() returns error or not, endio of epd->bio will be or has already been triggered thus free the bio. Either by successful bio submission, or by manual bio_endio(bio) call in submit_bio_hook. So in fact just setting "epd->bio =3D NULL" is completely fine in this context. Thanks, Qu >=20 > Thanks for pointing this problem out, > Qu >=20 --RPPaDlEQNLRQFmKwfDEfqDxXwqU6nNcMP-- --1vcLowf7xC0353BwxDhbzmkOT71jGxwAi Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAlxmjUIACgkQwj2R86El /qjv3wf+MiGHRzKleMIEKGAYU3NgFG7/FffiVu37HR3EBIWr1ewftGB2LPD4yNa/ 2rLHN723+qLyX7CdW/fkk/5nPEi+VK+3L0JyvFzD1ilmxDqQYH38bqzPBIpmdvUN 9ylRGuGE3KCoo6jjpqNXUuDudxIOCHxK3EIVXjyHQ5FvH3UghRglwGTDHYsv2E5w pcUP2zuxSIfJY65yv3gwX1tdlv35UnzZPexiZIikNGU6Wk1nLmvXdnz1ASh4fCGG b0D6HrEvUqo+rCeQSGEhhwMKr+fnw3ijUg7yQV6KniBlp7shhNpEo3Ij/ZLrnsCR R7XFrHq0ZRXED9K9d7sj6s5ORrPERw== =pJWU -----END PGP SIGNATURE----- --1vcLowf7xC0353BwxDhbzmkOT71jGxwAi--