From 808d2c94f53b9b29f44c2c5d9baea66d63ceddfc Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Wed, 14 Aug 2019 09:20:43 +0100 Subject: [PATCH 07/10] block: Fix AioContext switch for bs->drv == NULL RH-Author: Kevin Wolf Message-id: <20190814092043.15421-2-kwolf@redhat.com> Patchwork-id: 89976 O-Subject: [RHEL-8.1.0 qemu-kvm PATCH 1/1] block: Fix AioContext switch for bs->drv == NULL Bugzilla: 1716347 RH-Acked-by: Paolo Bonzini RH-Acked-by: Max Reitz RH-Acked-by: John Snow Even for block nodes with bs->drv == NULL, we can't just ignore a bdrv_set_aio_context() call. Leaving the node in its old context can mean that it's still in an iothread context in bdrv_close_all() during shutdown, resulting in an attempted unlock of the AioContext lock which we don't hold. This is an example stack trace of a related crash: #0 0x00007ffff59da57f in raise () at /lib64/libc.so.6 #1 0x00007ffff59c4895 in abort () at /lib64/libc.so.6 #2 0x0000555555b97b1e in error_exit (err=, msg=msg@entry=0x555555d386d0 <__func__.19059> "qemu_mutex_unlock_impl") at util/qemu-thread-posix.c:36 #3 0x0000555555b97f7f in qemu_mutex_unlock_impl (mutex=mutex@entry=0x5555568002f0, file=file@entry=0x555555d378df "util/async.c", line=line@entry=507) at util/qemu-thread-posix.c:97 #4 0x0000555555b92f55 in aio_context_release (ctx=ctx@entry=0x555556800290) at util/async.c:507 #5 0x0000555555b05cf8 in bdrv_prwv_co (child=child@entry=0x7fffc80012f0, offset=offset@entry=131072, qiov=qiov@entry=0x7fffffffd4f0, is_write=is_write@entry=true, flags=flags@entry=0) at block/io.c:833 #6 0x0000555555b060a9 in bdrv_pwritev (qiov=0x7fffffffd4f0, offset=131072, child=0x7fffc80012f0) at block/io.c:990 #7 0x0000555555b060a9 in bdrv_pwrite (child=0x7fffc80012f0, offset=131072, buf=, bytes=) at block/io.c:990 #8 0x0000555555ae172b in qcow2_cache_entry_flush (bs=bs@entry=0x555556810680, c=c@entry=0x5555568cc740, i=i@entry=0) at block/qcow2-cache.c:51 #9 0x0000555555ae18dd in qcow2_cache_write (bs=bs@entry=0x555556810680, c=0x5555568cc740) at block/qcow2-cache.c:248 #10 0x0000555555ae15de in qcow2_cache_flush (bs=0x555556810680, c=) at block/qcow2-cache.c:259 #11 0x0000555555ae16b1 in qcow2_cache_flush_dependency (c=0x5555568a1700, c=0x5555568a1700, bs=0x555556810680) at block/qcow2-cache.c:194 #12 0x0000555555ae16b1 in qcow2_cache_entry_flush (bs=bs@entry=0x555556810680, c=c@entry=0x5555568a1700, i=i@entry=0) at block/qcow2-cache.c:194 #13 0x0000555555ae18dd in qcow2_cache_write (bs=bs@entry=0x555556810680, c=0x5555568a1700) at block/qcow2-cache.c:248 #14 0x0000555555ae15de in qcow2_cache_flush (bs=bs@entry=0x555556810680, c=) at block/qcow2-cache.c:259 #15 0x0000555555ad242c in qcow2_inactivate (bs=bs@entry=0x555556810680) at block/qcow2.c:2124 #16 0x0000555555ad2590 in qcow2_close (bs=0x555556810680) at block/qcow2.c:2153 #17 0x0000555555ab0c62 in bdrv_close (bs=0x555556810680) at block.c:3358 #18 0x0000555555ab0c62 in bdrv_delete (bs=0x555556810680) at block.c:3542 #19 0x0000555555ab0c62 in bdrv_unref (bs=0x555556810680) at block.c:4598 #20 0x0000555555af4d72 in blk_remove_bs (blk=blk@entry=0x5555568103d0) at block/block-backend.c:785 #21 0x0000555555af4dbb in blk_remove_all_bs () at block/block-backend.c:483 #22 0x0000555555aae02f in bdrv_close_all () at block.c:3412 #23 0x00005555557f9796 in main (argc=, argv=, envp=) at vl.c:4776 The reproducer I used is a qcow2 image on gluster volume, where the virtual disk size (4 GB) is larger than the gluster volume size (64M), so we can easily trigger an ENOSPC. This backend is assigned to a virtio-blk device using an iothread, and then from the guest a 'dd if=/dev/zero of=/dev/vda bs=1G count=1' causes the VM to stop because of an I/O error. qemu_gluster_co_flush_to_disk() sets bs->drv = NULL on error, so when virtio-blk stops the dataplane, the block nodes stay in the iothread AioContext. A 'quit' monitor command issued from this paused state crashes the process. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1631227 Cc: qemu-stable@nongnu.org Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake Reviewed-by: Max Reitz Reviewed-by: Stefano Garzarella (cherry picked from commit 1bffe1ae7a7b707c3a14ea2ccd00d3609d3ce4d8) Signed-off-by: Kevin Wolf Signed-off-by: Danilo C. L. de Paula --- block.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/block.c b/block.c index 8f3ceea..37af100 100644 --- a/block.c +++ b/block.c @@ -4923,10 +4923,6 @@ void bdrv_detach_aio_context(BlockDriverState *bs) BdrvAioNotifier *baf, *baf_tmp; BdrvChild *child; - if (!bs->drv) { - return; - } - assert(!bs->walking_aio_notifiers); bs->walking_aio_notifiers = true; QLIST_FOREACH_SAFE(baf, &bs->aio_notifiers, list, baf_tmp) { @@ -4941,7 +4937,7 @@ void bdrv_detach_aio_context(BlockDriverState *bs) */ bs->walking_aio_notifiers = false; - if (bs->drv->bdrv_detach_aio_context) { + if (bs->drv && bs->drv->bdrv_detach_aio_context) { bs->drv->bdrv_detach_aio_context(bs); } QLIST_FOREACH(child, &bs->children, next) { @@ -4960,10 +4956,6 @@ void bdrv_attach_aio_context(BlockDriverState *bs, BdrvAioNotifier *ban, *ban_tmp; BdrvChild *child; - if (!bs->drv) { - return; - } - if (bs->quiesce_counter) { aio_disable_external(new_context); } @@ -4973,7 +4965,7 @@ void bdrv_attach_aio_context(BlockDriverState *bs, QLIST_FOREACH(child, &bs->children, next) { bdrv_attach_aio_context(child->bs, new_context); } - if (bs->drv->bdrv_attach_aio_context) { + if (bs->drv && bs->drv->bdrv_attach_aio_context) { bs->drv->bdrv_attach_aio_context(bs, new_context); } -- 1.8.3.1