From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:46655) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RXZNl-0001cQ-M1 for qemu-devel@nongnu.org; Mon, 05 Dec 2011 09:19:07 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RXZNg-0000O9-Nc for qemu-devel@nongnu.org; Mon, 05 Dec 2011 09:19:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52051) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RXZNg-0000Nz-A0 for qemu-devel@nongnu.org; Mon, 05 Dec 2011 09:18:56 -0500 From: Kevin Wolf Date: Mon, 5 Dec 2011 15:21:17 +0100 Message-Id: <1323094878-7967-41-git-send-email-kwolf@redhat.com> In-Reply-To: <1323094878-7967-1-git-send-email-kwolf@redhat.com> References: <1323094878-7967-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 40/41] block: wait_for_overlapping_requests() deadlock detection List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Stefan Hajnoczi 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 Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- block.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-) diff --git a/block.c b/block.c index ecc5b44..50ce2be 100644 --- a/block.c +++ b/block.c @@ -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; -- 1.7.6.4