From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51561) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCqnz-00018H-40 for qemu-devel@nongnu.org; Tue, 14 Jun 2016 12:03:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bCqnu-0003p3-WE for qemu-devel@nongnu.org; Tue, 14 Jun 2016 12:03:07 -0400 Received: from mo53.mail-out.ovh.net ([178.32.228.53]:33152) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bCqnu-0003oq-Le for qemu-devel@nongnu.org; Tue, 14 Jun 2016 12:03:02 -0400 Received: from player159.ha.ovh.net (b9.ovh.net [213.186.33.59]) by mo53.mail-out.ovh.net (Postfix) with ESMTP id CE79DFF8EDB for ; Tue, 14 Jun 2016 18:03:00 +0200 (CEST) References: <1464694565-16784-1-git-send-email-clg@kaod.org> <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> From: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= Message-ID: <57602AAC.1050304@kaod.org> Date: Tue, 14 Jun 2016 18:02:52 +0200 MIME-Version: 1.0 In-Reply-To: <20160614083832.GC4916@noname.str.redhat.com> Content-Type: text/plain; charset=windows-1252 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: Kevin Wolf Cc: Eric Blake , Peter Crosthwaite , Max Reitz , qemu-block@nongnu.org, qemu-devel@nongnu.org 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=3D0x7fa81d4dd050,= 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, offs= et=3D8, bytes=3D512, qiov=3D0x7fa80d5191c0,=20 >>>> flags=3D(BDRV_REQ_COPY_ON_READ | BDRV_REQ_ZERO_WRITE | BDRV_REQ_= MAY_UNMAP | BDRV_REQ_NO_SERIALISING | BDRV_REQ_FUA | unknown: 4278124256)= , 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, offs= et=3D30878208, bytes=3D256, qiov=3D0x7fa80d5191c0,=20 >>>> flags=3D(unknown: 0)) at /home/legoater/work/qemu/qemu-ast2400-m= ainline.git/block/block-backend.c:788 >>>> #7 0x00007fa81c65e49b in blk_aio_write_entry (opaque=3D0x7fa7e849ac= a0) >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/bloc= k-backend.c:977 >>>> #8 0x00007fa81c6c823a in coroutine_trampoline (i0=3D= , i1=3D) >>>> at /home/legoater/work/qemu/qemu-ast2400-mainline.git/util/corou= tine-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 coroutines,= to >>> see who's sending the bad parameters. I recently debugged a bogus fl= ags >>> in bdrv_aio_preadv, by hoisting an assert to occur before coroutines = 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, and= /or >>> the hack for catching the bug prior to coroutines, will help you debu= g >>> 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=3D0x7fa81d4dd050,= 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 2= 56} >> >> So, it seems that the issue is coming from the fact that bdrv_co_pwrit= ev() >> 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 latte= r > function). >=20 > It's just unclear to me why this code extended bytes, but didn't add th= e > tail_buf iovec to local_qiov. The gdb backtrace is bogus. It does not make sense. May be a gdb issue with multithread on jessie. In the path tracking the tail bytes, we have :=20 if ((offset + bytes) & (align - 1)) { ... tail_bytes =3D (offset + bytes) & (align - 1); qemu_iovec_add(&local_qiov, tail_buf + tail_bytes, align - tail_b= ytes); bytes =3D ROUND_UP(bytes, align); } This is where the issue is I think. The qiov holds 256 and bytes 512. I have no idea how to fix that though. Thanks, C.=20