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[Qemu-commits] [qemu/qemu] cf4fbc: block/nvme: fix infinite loop in nvme

From: Richard Henderson
Subject: [Qemu-commits] [qemu/qemu] cf4fbc: block/nvme: fix infinite loop in nvme_free_req_que...
Date: Tue, 14 Dec 2021 14:36:42 -0800

  Branch: refs/heads/master
  Home:   https://github.com/qemu/qemu
  Commit: cf4fbc3030c974fff726756a7ceef8386cdf500b
  Author: Stefan Hajnoczi <stefanha@redhat.com>
  Date:   2021-12-09 (Thu, 09 Dec 2021)

  Changed paths:
    M block/nvme.c

  Log Message:
  block/nvme: fix infinite loop in nvme_free_req_queue_cb()

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 <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20211208152246.244585-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

  Commit: 76b56fdfc9fa43ec6e5986aee33f108c6c6a511e
  Author: Richard Henderson <richard.henderson@linaro.org>
  Date:   2021-12-14 (Tue, 14 Dec 2021)

  Changed paths:
    M block/nvme.c

  Log Message:
  Merge tag 'block-pull-request' of https://gitlab.com/stefanha/qemu into 

Pull request

An infinite loop fix for the userspace NVMe driver.

# gpg: Signature made Thu 09 Dec 2021 07:21:08 AM PST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]

* tag 'block-pull-request' of https://gitlab.com/stefanha/qemu:
  block/nvme: fix infinite loop in nvme_free_req_queue_cb()

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Compare: https://github.com/qemu/qemu/compare/af1719795c88...76b56fdfc9fa

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