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block: wait_for_overlapping_requests() deadlock detection 

Debugging a reentrant request deadlock was fun but in the future we need
a quick and obvious way of detecting such bugs.  Add an assert that
checks we are not about to deadlock when waiting for another request.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2011-11-30 12:23:42 +00:00 committed by Kevin Wolf
parent bd9533e36e
commit 5f8b6491f2
1 changed files with 8 additions and 0 deletions
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8
block.c
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@ -1099,6 +1099,7 @@ struct BdrvTrackedRequest {
int nb_sectors;
bool is_write;
QLIST_ENTRY(BdrvTrackedRequest) list;
Coroutine *co; /* owner, used for deadlock detection */
CoQueue wait_queue; /* coroutines blocked on this request */
};
@ -1126,6 +1127,7 @@ static void tracked_request_begin(BdrvTrackedRequest *req,
.sector_num = sector_num,
.nb_sectors = nb_sectors,
.is_write = is_write,
.co = qemu_coroutine_self(),
};
qemu_co_queue_init(&req->wait_queue);
@ -1189,6 +1191,12 @@ static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
QLIST_FOREACH(req, &bs->tracked_requests, list) {
if (tracked_request_overlaps(req, cluster_sector_num,
cluster_nb_sectors)) {
/* Hitting this means there was a reentrant request, for
* example, a block driver issuing nested requests. This must
* never happen since it means deadlock.
*/
assert(qemu_coroutine_self() != req->co);
qemu_co_queue_wait(&req->wait_queue);
retry = true;
break;