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block: protect BlockBackend->queued_requests with a lock 

The CoQueue API offers thread-safety via the lock argument that
qemu_co_queue_wait() and qemu_co_enter_next() take. BlockBackend
currently does not make use of the lock argument. This means that
multiple threads submitting I/O requests can corrupt the CoQueue's
QSIMPLEQ.

Add a QemuMutex and pass it to CoQueue APIs so that the queue is
protected. While we're at it, also assert that the queue is empty when
the BlockBackend is deleted.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230307210427.269214-4-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-03-07 16:04:27 -05:00 committed by Kevin Wolf
parent ef80ec5067
commit 407ae2ae07
1 changed files with 16 additions and 2 deletions
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18
block/block-backend.c
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@ -81,6 +81,7 @@ struct BlockBackend {
QLIST_HEAD(, BlockBackendAioNotifier) aio_notifiers;
int quiesce_counter; /* atomic: written under BQL, read by other threads */
QemuMutex queued_requests_lock; /* protects queued_requests */
CoQueue queued_requests;
bool disable_request_queuing; /* atomic */
@ -368,6 +369,7 @@ BlockBackend *blk_new(AioContext *ctx, uint64_t perm, uint64_t shared_perm)
block_acct_init(&blk->stats);
qemu_mutex_init(&blk->queued_requests_lock);
qemu_co_queue_init(&blk->queued_requests);
notifier_list_init(&blk->remove_bs_notifiers);
notifier_list_init(&blk->insert_bs_notifiers);
@ -485,6 +487,8 @@ static void blk_delete(BlockBackend *blk)
assert(QLIST_EMPTY(&blk->remove_bs_notifiers.notifiers));
assert(QLIST_EMPTY(&blk->insert_bs_notifiers.notifiers));
assert(QLIST_EMPTY(&blk->aio_notifiers));
assert(qemu_co_queue_empty(&blk->queued_requests));
qemu_mutex_destroy(&blk->queued_requests_lock);
QTAILQ_REMOVE(&block_backends, blk, link);
drive_info_del(blk->legacy_dinfo);
block_acct_cleanup(&blk->stats);
@ -1273,9 +1277,16 @@ static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
if (qatomic_read(&blk->quiesce_counter) &&
!qatomic_read(&blk->disable_request_queuing)) {
/*
* Take lock before decrementing in flight counter so main loop thread
* waits for us to enqueue ourselves before it can leave the drained
* section.
*/
qemu_mutex_lock(&blk->queued_requests_lock);
blk_dec_in_flight(blk);
qemu_co_queue_wait(&blk->queued_requests, NULL);
qemu_co_queue_wait(&blk->queued_requests, &blk->queued_requests_lock);
blk_inc_in_flight(blk);
qemu_mutex_unlock(&blk->queued_requests_lock);
}
}
@ -2634,9 +2645,12 @@ static void blk_root_drained_end(BdrvChild *child)
if (blk->dev_ops && blk->dev_ops->drained_end) {
blk->dev_ops->drained_end(blk->dev_opaque);
}
while (qemu_co_enter_next(&blk->queued_requests, NULL)) {
qemu_mutex_lock(&blk->queued_requests_lock);
while (qemu_co_enter_next(&blk->queued_requests,
&blk->queued_requests_lock)) {
/* Resume all queued requests */
}
qemu_mutex_unlock(&blk->queued_requests_lock);
}
}