Commit 6460440f authored by Kevin Wolf's avatar Kevin Wolf

block: Allow wait_serialising_requests() at any point

We can only have a single wait_serialising_requests() call per request
because otherwise we can run into deadlocks where requests are waiting
for each other. The same is true when wait_serialising_requests() is not
at the very beginning of a request, so that other requests can be issued
between the start of the tracking and wait_serialising_requests().

Fix this by changing wait_serialising_requests() to ignore requests that
are already (directly or indirectly) waiting for the calling request.
Signed-off-by: default avatarKevin Wolf <>
Reviewed-by: default avatarMax Reitz <>
Reviewed-by: default avatarBenoit Canet <>
parent 7327145f
......@@ -2328,9 +2328,16 @@ static void coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
assert(qemu_coroutine_self() != req->co);
retry = true;
/* If the request is already (indirectly) waiting for us, or
* will wait for us as soon as it wakes up, then just go on
* (instead of producing a deadlock in the former case). */
if (!req->waiting_for) {
self->waiting_for = req;
self->waiting_for = NULL;
retry = true;
} while (retry);
......@@ -68,6 +68,8 @@ typedef struct BdrvTrackedRequest {
QLIST_ENTRY(BdrvTrackedRequest) list;
Coroutine *co; /* owner, used for deadlock detection */
CoQueue wait_queue; /* coroutines blocked on this request */
struct BdrvTrackedRequest *waiting_for;
} BdrvTrackedRequest;
struct BlockDriver {
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