From 30dd65f307b647eef8156c4a33bd007823ef85cb Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Tue, 10 Mar 2020 12:38:29 +0100 Subject: [PATCH] block: Fix cross-AioContext blockdev-snapshot external_snapshot_prepare() tries to move the overlay to the AioContext of the backing file (the snapshotted node). However, it's possible that this doesn't work, but the backing file can instead be moved to the overlay's AioContext (e.g. opening the backing chain for a mirror target). bdrv_append() already indirectly uses bdrv_attach_node(), which takes care to move nodes to make sure they use the same AioContext and which tries both directions. So the problem has a simple fix: Just delete the unnecessary extra bdrv_try_set_aio_context() call in external_snapshot_prepare() and instead assert in bdrv_append() that both nodes were indeed moved to the same AioContext. Signed-off-by: Kevin Wolf Message-Id: <20200310113831.27293-6-kwolf@redhat.com> Tested-by: Peter Krempa Signed-off-by: Kevin Wolf --- block.c | 1 + blockdev.c | 16 ---------------- 2 files changed, 1 insertion(+), 16 deletions(-) diff --git a/block.c b/block.c index 79a5a2770f..8fc7b56937 100644 --- a/block.c +++ b/block.c @@ -4365,6 +4365,7 @@ void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to, bdrv_ref(from); assert(qemu_get_current_aio_context() == qemu_get_aio_context()); + assert(bdrv_get_aio_context(from) == bdrv_get_aio_context(to)); bdrv_drained_begin(from); /* Put all parents into @list and calculate their cumulative permissions */ diff --git a/blockdev.c b/blockdev.c index ea89896f27..fa8630cb41 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1470,9 +1470,7 @@ static void external_snapshot_prepare(BlkActionState *common, DO_UPCAST(ExternalSnapshotState, common, common); TransactionAction *action = common->action; AioContext *aio_context; - AioContext *old_context; uint64_t perm, shared; - int ret; /* 'blockdev-snapshot' and 'blockdev-snapshot-sync' have similar * purpose but a different set of parameters */ @@ -1608,20 +1606,6 @@ static void external_snapshot_prepare(BlkActionState *common, goto out; } - /* Honor bdrv_try_set_aio_context() context acquisition requirements. */ - old_context = bdrv_get_aio_context(state->new_bs); - aio_context_release(aio_context); - aio_context_acquire(old_context); - - ret = bdrv_try_set_aio_context(state->new_bs, aio_context, errp); - - aio_context_release(old_context); - aio_context_acquire(aio_context); - - if (ret < 0) { - goto out; - } - /* This removes our old bs and adds the new bs. This is an operation that * can fail, so we need to do it in .prepare; undoing it for abort is * always possible. */