From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55722) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YL87w-0007w4-RH for qemu-devel@nongnu.org; Tue, 10 Feb 2015 05:33:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YL87t-0006H8-Jx for qemu-devel@nongnu.org; Tue, 10 Feb 2015 05:33:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56212) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YL87t-0006H2-Cv for qemu-devel@nongnu.org; Tue, 10 Feb 2015 05:33:05 -0500 Date: Tue, 10 Feb 2015 11:32:59 +0100 From: Kevin Wolf Message-ID: <20150210103259.GC5202@noname.str.redhat.com> References: <1423545380-8748-1-git-send-email-wu.wubin@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1423545380-8748-1-git-send-email-wu.wubin@huawei.com> Subject: Re: [Qemu-devel] [PATCH v3] qemu-coroutine: segfault when restarting co_queue List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bin Wu Cc: pbonzini@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com Am 10.02.2015 um 06:16 hat Bin Wu geschrieben: > From: Bin Wu > > We tested VMs migration with their disk images by drive_mirror. With > migration, two VMs copyed large files between each other. During the > test, a segfault occured. The stack was as follow: > > 00) 0x00007fa5a0c63fc5 in qemu_co_queue_run_restart (co=0x7fa5a1798648) at > qemu-coroutine-lock.c:66 > 01) 0x00007fa5a0c63bed in coroutine_swap (from=0x7fa5a178f160, > to=0x7fa5a1798648) at qemu-coroutine.c:97 > 02) 0x00007fa5a0c63dbf in qemu_coroutine_yield () at qemu-coroutine.c:140 > 03) 0x00007fa5a0c9e474 in nbd_co_receive_reply (s=0x7fa5a1a3cfd0, > request=0x7fa28c2ffa10, reply=0x7fa28c2ffa30, qiov=0x0, offset=0) at > block/nbd-client.c:165 > 04) 0x00007fa5a0c9e8b5 in nbd_co_writev_1 (client=0x7fa5a1a3cfd0, > sector_num=8552704, nb_sectors=2040, qiov=0x7fa5a1757468, offset=0) at > block/nbd-client.c:262 > 05) 0x00007fa5a0c9e9dd in nbd_client_session_co_writev (client=0x7fa5a1a3cfd0, > sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468) at > block/nbd-client.c:296 > 06) 0x00007fa5a0c9dda1 in nbd_co_writev (bs=0x7fa5a198fcb0, sector_num=8552704, > nb_sectors=2048, qiov=0x7fa5a1757468) at block/nbd.c:291 > 07) 0x00007fa5a0c509a4 in bdrv_aligned_pwritev (bs=0x7fa5a198fcb0, > req=0x7fa28c2ffbb0, offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, > flags=0) at block.c:3321 > 08) 0x00007fa5a0c50f3f in bdrv_co_do_pwritev (bs=0x7fa5a198fcb0, > offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, flags=(unknown: 0)) at > block.c:3447 > 09) 0x00007fa5a0c51007 in bdrv_co_do_writev (bs=0x7fa5a198fcb0, > sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468, flags=(unknown: 0)) at > block.c:3471 > 10) 0x00007fa5a0c51074 in bdrv_co_writev (bs=0x7fa5a198fcb0, sector_num=8552704, > nb_sectors=2048, qiov=0x7fa5a1757468) at block.c:3480 > 11) 0x00007fa5a0c652ec in raw_co_writev (bs=0x7fa5a198c110, sector_num=8552704, > nb_sectors=2048, qiov=0x7fa5a1757468) at block/raw_bsd.c:62 > 12) 0x00007fa5a0c509a4 in bdrv_aligned_pwritev (bs=0x7fa5a198c110, > req=0x7fa28c2ffe30, offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, > flags=0) at block.c:3321 > 13) 0x00007fa5a0c50f3f in bdrv_co_do_pwritev (bs=0x7fa5a198c110, > offset=4378984448, bytes=1048576, qiov=0x7fa5a1757468, flags=(unknown: 0)) at > block.c:3447 > 14) 0x00007fa5a0c51007 in bdrv_co_do_writev (bs=0x7fa5a198c110, > sector_num=8552704, nb_sectors=2048, qiov=0x7fa5a1757468, flags=(unknown: 0)) at > block.c:3471 > 15) 0x00007fa5a0c542b3 in bdrv_co_do_rw (opaque=0x7fa5a17a0000) at block.c:4706 > 16) 0x00007fa5a0c64e6e in coroutine_trampoline (i0=-1585909408, i1=32677) at > coroutine-ucontext.c:121 > 17) 0x00007fa59dc5aa50 in __correctly_grouped_prefixwc () from /lib64/libc.so.6 > 18) 0x0000000000000000 in ?? () > > After analyzing the stack and reviewing the code, we find the > qemu_co_queue_run_restart should not be put in the coroutine_swap function which > can be invoked by qemu_coroutine_enter or qemu_coroutine_yield. Only > qemu_coroutine_enter needs to restart the co_queue. > > The error scenario is as follow: coroutine C1 enters C2, C2 yields > back to C1, then C1 ternimates and the related coroutine memory > becomes invalid. After a while, the C2 coroutine is entered again. > At this point, C1 is used as a parameter passed to > qemu_co_queue_run_restart. Therefore, qemu_co_queue_run_restart > accesses an invalid memory and a segfault error ocurrs. > > The qemu_co_queue_run_restart function re-enters coroutines waiting > in the co_queue. However, this function should be only used int the > qemu_coroutine_enter context. Only in this context, when the current > coroutine gets execution control again(after the execution of > qemu_coroutine_switch), we can restart the target coutine because the > target coutine has yielded back to the current coroutine or it has > terminated. > > First we want to put qemu_co_queue_run_restart in qemu_coroutine_enter, > but we find we can not access the target coroutine if it terminates. > > Signed-off-by: Bin Wu As I replied for v2, I'll send a series with a simpler fix and some cleanup that should result in a nicer design in the end. Kevin