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block: temporarily hold the new AioContext of bs_top in bdrv_append() 

bdrv_append() is called with bs_top AioContext held, but
bdrv_attach_child_noperm() could change the AioContext of bs_top.

bdrv_replace_node_noperm() calls bdrv_drained_begin() starting from
commit 2398747128 ("block: Don't poll in bdrv_replace_child_noperm()").
bdrv_drained_begin() can call BDRV_POLL_WHILE that assumes the new lock
is taken, so let's temporarily hold the new AioContext to prevent QEMU
from failing in BDRV_POLL_WHILE when it tries to release the wrong
AioContext.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2168209
Reported-by: Aihua Liang <aliang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20230214171621.11574-1-sgarzare@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefano Garzarella 2023-02-14 18:16:21 +01:00 committed by Kevin Wolf
parent e7b8d9d038
commit 60d90bf43c
1 changed files with 23 additions and 0 deletions
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23
block.c
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@ -5265,6 +5265,8 @@ int bdrv_drop_filter(BlockDriverState *bs, Error **errp)
* child.
*
* This function does not create any image files.
*
* The caller must hold the AioContext lock for @bs_top.
*/
int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
Error **errp)
@ -5272,11 +5274,14 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
int ret;
BdrvChild *child;
Transaction *tran = tran_new();
AioContext *old_context, *new_context = NULL;
GLOBAL_STATE_CODE();
assert(!bs_new->backing);
old_context = bdrv_get_aio_context(bs_top);
child = bdrv_attach_child_noperm(bs_new, bs_top, "backing",
&child_of_bds, bdrv_backing_role(bs_new),
tran, errp);
@ -5285,6 +5290,19 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
goto out;
}
/*
* bdrv_attach_child_noperm could change the AioContext of bs_top.
* bdrv_replace_node_noperm calls bdrv_drained_begin, so let's temporarily
* hold the new AioContext, since bdrv_drained_begin calls BDRV_POLL_WHILE
* that assumes the new lock is taken.
*/
new_context = bdrv_get_aio_context(bs_top);
if (old_context != new_context) {
aio_context_release(old_context);
aio_context_acquire(new_context);
}
ret = bdrv_replace_node_noperm(bs_top, bs_new, true, tran, errp);
if (ret < 0) {
goto out;
@ -5296,6 +5314,11 @@ out:
bdrv_refresh_limits(bs_top, NULL, NULL);
if (new_context && old_context != new_context) {
aio_context_release(new_context);
aio_context_acquire(old_context);
}
return ret;
}