[Bug 288345] poudriere run, hanging umounts, system fails to reboot due to hanging processes

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=288345

--- Comment #57 from commit-hook@FreeBSD.org ---
A commit in branch stable/15 references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=d86a85e9b5ecc59754616edcd915e7d9eae9bab1

commit d86a85e9b5ecc59754616edcd915e7d9eae9bab1
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2026-02-25 15:31:30 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2026-03-31 15:57:29 +0000

    nullfs: Fix handling of doomed vnodes in nullfs_unlink_lowervp()

    nullfs_unlink_lowervp() is called with the lower vnode locked, so the
    nullfs vnode is locked too.  The following can occur:
    1. the vunref() call decrements the usecount 2->1,
    2. a different thread calls vrele() on the vnode, decrements the
       usecount 0->1, then blocks on the vnode lock,
    3. the first thread tests vp->v_usecount == 0 and observes that it is
       true,
    4. the first thread incorrectly unlocks the lower vnode.

    Fix this by testing VN_IS_DOOMED directly.  Since
    nullfs_unlink_lowervp() holds the vnode lock, the value of the
    VIRF_DOOMED flag is stable.

    Thanks to leres@ for patiently helping to track this down.

    PR:             288345
    MFC after:      1 week
    Reviewed by:    kib
    Differential Revision:  https://reviews.freebsd.org/D55446

    (cherry picked from commit 8b64d46fab87af3ae062901312187f3a04ad2d67)

 sys/fs/nullfs/null_vfsops.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

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