From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bD5hM-0003Xh-U8 for qemu-devel@nongnu.org; Wed, 15 Jun 2016 03:57:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bD5hK-0001MM-MU for qemu-devel@nongnu.org; Wed, 15 Jun 2016 03:57:15 -0400 Date: Wed, 15 Jun 2016 09:57:04 +0200 From: Kevin Wolf Message-ID: <20160615075704.GC4566@noname.redhat.com> References: <574D9F0F.7060904@redhat.com> <574D9FBB.60100@kaod.org> <574DA17D.5070505@redhat.com> <575EDE86.6080201@kaod.org> <575EE3B7.5080209@redhat.com> <575EF0AC.20305@kaod.org> <575F01EE.2050208@redhat.com> <575FB9F9.4000003@kaod.org> <20160614083832.GC4916@noname.str.redhat.com> <57602AAC.1050304@kaod.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <57602AAC.1050304@kaod.org> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] m25p80: fix test on blk_pread() return value List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?iso-8859-1?Q?C=E9dric?= Le Goater Cc: Eric Blake , Peter Crosthwaite , Max Reitz , qemu-block@nongnu.org, qemu-devel@nongnu.org Am 14.06.2016 um 18:02 hat C=E9dric Le Goater geschrieben: > On 06/14/2016 10:38 AM, Kevin Wolf wrote: > > Am 14.06.2016 um 10:02 hat C=E9dric Le Goater geschrieben: > >>>> #4 0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=3D0x7fa81d4dd05= 0, req=3D, offset=3D30878208,=20 > >>>> bytes=3D512, qiov=3D0x7fa7f47fee60, flags=3D0) > >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io= .c:1243 > >>>> #5 0x00007fa81c669ecb in bdrv_co_pwritev (bs=3D0x7fa81d4dd050, of= fset=3D8, bytes=3D512, qiov=3D0x7fa80d5191c0,=20 > >>>> flags=3D(BDRV_REQ_COPY_ON_READ | BDRV_REQ_ZERO_WRITE | BDRV_RE= Q_MAY_UNMAP | BDRV_REQ_NO_SERIALISING | BDRV_REQ_FUA | unknown: 427812425= 6), flags@entry=3D(unknown: 0)) > >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io= .c:1492 > >>> > >>> That 'flags' value looks bogus... > >>> > >>>> #6 0x00007fa81c65e367 in blk_co_pwritev (blk=3D0x7fa81d4c5b60, of= fset=3D30878208, bytes=3D256, qiov=3D0x7fa80d5191c0,=20 > >>>> flags=3D(unknown: 0)) at /home/legoater/work/qemu/qemu-ast2400= -mainline.git/block/block-backend.c:788 > >>>> #7 0x00007fa81c65e49b in blk_aio_write_entry (opaque=3D0x7fa7e849= aca0) > >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/bl= ock-backend.c:977 > >>>> #8 0x00007fa81c6c823a in coroutine_trampoline (i0=3D, i1=3D) > >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/util/cor= outine-ucontext.c:78 > >>>> #9 0x00007fa818ea8f00 in ?? () from /lib/x86_64-linux-gnu/libc.so= .6 > >>> > >>> and we don't get anything further in the backtrace beyond coroutine= s, to > >>> see who's sending the bad parameters. I recently debugged a bogus = flags > >>> in bdrv_aio_preadv, by hoisting an assert to occur before coroutine= s are > >>> used in blk_aio_prwv(): > >>> > >>> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02948.html > >>> > >>> I've just posted v2 of that patch (now a 2/2 series), but in v2 no > >>> longer kept the assert at that point. But maybe the correct fix, a= nd/or > >>> the hack for catching the bug prior to coroutines, will help you de= bug > >>> where the bad arguments are coming from. > >> > >> That does not fix the assert. > >> =20 > >>>> #10 0x00007fa80d5189d0 in ?? () > >>>> #11 0x0000000000000000 in ?? () > >>>> (gdb) up 4 > >>>> #4 0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=3D0x7fa81d4dd05= 0, req=3D, offset=3D30878208,=20 > >>>> bytes=3D512, qiov=3D0x7fa7f47fee60, flags=3D0) > >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io= .c:1243 > >>>> 1243 assert(!qiov || bytes =3D=3D qiov->size); > >>>> (gdb) p *qiov=20 > >>>> $1 =3D {iov =3D 0x7fa81da671d0, niov =3D 1, nalloc =3D 1, size =3D= 256} > >> > >> So, it seems that the issue is coming from the fact that bdrv_co_pwr= itev() > >> does not handle alignments less than BDRV_SECTOR_SIZE : > >> > >> /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface = */ > >> uint64_t align =3D MAX(BDRV_SECTOR_SIZE, bs->request_alignment); > >> > >> It calls bdrv_aligned_pwritev() which does the assert :=20 > >> > >> assert(!qiov || bytes =3D=3D qiov->size); > >=20 > > Yes, but between these two places, there is code that should actually > > enforce the right alignment: > >=20 > > if ((offset + bytes) & (align - 1)) { > > ... > > } > >=20 > > You can see in your backtrace that bdrv_aligned_pwritev() gets a > > different qiov than bdrv_co_pwritev() (which is local_qiov in the lat= ter > > function). > >=20 > > It's just unclear to me why this code extended bytes, but didn't add = the > > tail_buf iovec to local_qiov. >=20 > The gdb backtrace is bogus. It does not make sense. May be a gdb issue > with multithread on jessie. >=20 > In the path tracking the tail bytes, we have :=20 >=20 > if ((offset + bytes) & (align - 1)) { > ... if (!use_local_qiov) { qemu_iovec_init(&local_qiov, qiov->niov + 1); qemu_iovec_concat(&local_qiov, qiov, 0, qiov->size); use_local_qiov =3D true; } > tail_bytes =3D (offset + bytes) & (align - 1); > qemu_iovec_add(&local_qiov, tail_buf + tail_bytes, align - tail= _bytes); >=20 > bytes =3D ROUND_UP(bytes, align); > } >=20 > This is where the issue is I think. The qiov holds 256 and bytes 512. >=20 > I have no idea how to fix that though. Added some more context above. qiov->size as passed from the device is already 256 bytes, which are added to local_qiov with qemu_iovec_concat(). And then we add another 256 from tail_buf in the lines that you quoted, so in theory we should end up with a properly aligned 256 + 256 =3D 512 byte qiov. Kevin