From 6989be9d0aa08470f8b287c243dc4bf027d5fbcf Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 8 Dec 2021 15:22:46 +0000 Subject: [PATCH 1/2] block/nvme: fix infinite loop in nvme_free_req_queue_cb() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Stefan Hajnoczi RH-MergeRequest: 58: block/nvme: fix infinite loop in nvme_free_req_queue_cb() RH-Commit: [1/1] 544b3f310d791a20c63b51947de0c6cbb60b0d5b (stefanha/centos-stream-qemu-kvm) RH-Bugzilla: 2024544 RH-Acked-by: Kevin Wolf RH-Acked-by: Stefano Garzarella RH-Acked-by: Hanna Reitz When the request free list is exhausted the coroutine waits on q->free_req_queue for the next free request. Whenever a request is completed a BH is scheduled to invoke nvme_free_req_queue_cb() and wake up waiting coroutines. 1. nvme_get_free_req() waits for a free request: while (q->free_req_head == -1) { ... trace_nvme_free_req_queue_wait(q->s, q->index); qemu_co_queue_wait(&q->free_req_queue, &q->lock); ... } 2. nvme_free_req_queue_cb() wakes up the coroutine: while (qemu_co_enter_next(&q->free_req_queue, &q->lock)) { ^--- infinite loop when free_req_head == -1 } nvme_free_req_queue_cb() and the coroutine form an infinite loop when q->free_req_head == -1. Fix this by checking q->free_req_head in nvme_free_req_queue_cb(). If the free request list is exhausted, don't wake waiting coroutines. Eventually an in-flight request will complete and the BH will be scheduled again, guaranteeing forward progress. Signed-off-by: Stefan Hajnoczi Reviewed-by: Philippe Mathieu-Daudé Message-id: 20211208152246.244585-1-stefanha@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit cf4fbc3030c974fff726756a7ceef8386cdf500b) Signed-off-by: Stefan Hajnoczi --- block/nvme.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/block/nvme.c b/block/nvme.c index e4f336d79c..fa360b9b3c 100644 --- a/block/nvme.c +++ b/block/nvme.c @@ -206,8 +206,9 @@ static void nvme_free_req_queue_cb(void *opaque) NVMeQueuePair *q = opaque; qemu_mutex_lock(&q->lock); - while (qemu_co_enter_next(&q->free_req_queue, &q->lock)) { - /* Retry all pending requests */ + while (q->free_req_head != -1 && + qemu_co_enter_next(&q->free_req_queue, &q->lock)) { + /* Retry waiting requests */ } qemu_mutex_unlock(&q->lock); } -- 2.27.0