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