From 6460440f34c709461b84375cfd8a86b27d433225 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Fri, 13 Dec 2013 13:04:35 +0100 Subject: 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: Kevin Wolf Reviewed-by: Max Reitz Reviewed-by: Benoit Canet --- block.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index 784ff079ed..96905856a1 100644 --- a/block.c +++ b/block.c @@ -2328,9 +2328,16 @@ static void coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self) */ assert(qemu_coroutine_self() != req->co); - qemu_co_queue_wait(&req->wait_queue); - retry = true; - break; + /* 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; + qemu_co_queue_wait(&req->wait_queue); + self->waiting_for = NULL; + retry = true; + break; + } } } } while (retry); -- cgit v1.2.1