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qcow2: Fix open with 'file' in iothread 

qcow2_open() doesn't work correctly when opening the 'file' child moves
bs to an iothread, for several reasons:

- It uses BDRV_POLL_WHILE() to wait for the qcow2_open_entry()
  coroutine, which involves dropping the AioContext lock for bs when it
  is not in the main context - but we don't hold it, so this crashes.

- It runs the qcow2_open_entry() coroutine in the current thread instead
  of the new AioContext of bs.

- qcow2_open_entry() doesn't notify the main loop when it's done.

This patches fixes these issues around delegating work to a coroutine.
Temporarily dropping the main AioContext lock is not necessary because
we know we run in the main thread.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-7-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
master
Kevin Wolf 2023-05-25 14:47:07 +02:00
parent 2626d27f50
commit aa269ff888
2 changed files with 12 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
block.c
View File

@ -3646,6 +3646,9 @@ done:
* BlockdevRef.
*
* The BlockdevRef will be removed from the options QDict.
*
* @parent can move to a different AioContext in this function. Callers must
* make sure that their AioContext locking is still correct after this.
*/
BdrvChild *bdrv_open_child(const char *filename,
QDict *options, const char *bdref_key,
@ -3670,6 +3673,9 @@ BdrvChild *bdrv_open_child(const char *filename,
/*
* Wrapper on bdrv_open_child() for most popular case: open primary child of bs.
*
* @parent can move to a different AioContext in this function. Callers must
* make sure that their AioContext locking is still correct after this.
*/
int bdrv_open_file_child(const char *filename,
QDict *options, const char *bdref_key,

8
block/qcow2.c
View File

@ -1904,6 +1904,8 @@ static void coroutine_fn qcow2_open_entry(void *opaque)
qoc->ret = qcow2_do_open(qoc->bs, qoc->options, qoc->flags, true,
qoc->errp);
qemu_co_mutex_unlock(&s->lock);
aio_wait_kick();
}
static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
@ -1929,8 +1931,10 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
assert(!qemu_in_coroutine());
assert(qemu_get_current_aio_context() == qemu_get_aio_context());
qemu_coroutine_enter(qemu_coroutine_create(qcow2_open_entry, &qoc));
BDRV_POLL_WHILE(bs, qoc.ret == -EINPROGRESS);
aio_co_enter(bdrv_get_aio_context(bs),
qemu_coroutine_create(qcow2_open_entry, &qoc));
AIO_WAIT_WHILE_UNLOCKED(NULL, qoc.ret == -EINPROGRESS);
return qoc.ret;
}