[Bug 289930] Booting FreeBSD 16-CURRENT on riscv64 with QEMU hangs indefinitely

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=289930

--- Comment #4 from commit-hook@FreeBSD.org ---
A commit in branch releng/15.0 references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=69c726c150772c36854d38e51b6fd921a04caea5

commit 69c726c150772c36854d38e51b6fd921a04caea5
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-11-04 14:27:33 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2025-11-07 23:12:02 +0000

    virtio: Fix polling in virtqueue_dequeue()

    The access of vq->vq_ring.used->idx needs to be volatile-qualified,
    otherwise the compiler may optimize virtqueue_poll() into an infinite
    loop if there is no data available upon the first poll.

    Prior to commit ad17789a8569 this wasn't a problem since an external
    function call after each poll inhibited the optimization.

    Approved by:    re (cperciva)
    PR:             289930
    MFC after:      3 days
    Sponsored by:   Klara, Inc.
    Fixes:          ad17789a8569 ("virtio: Remove the unused poll method")

    (cherry picked from commit f999ffdce3813eb946f10999ccffb8275c324469)
    (cherry picked from commit 72c76047541ab6cc0e989a74e8de4d6e6a1a94b6)

 sys/dev/virtio/virtqueue.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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