[Bug 297174] nullfs: panic: self-referential mount on tmpfs: recursing lock (CURRENT, 15.1-RELEASE-p2)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=297174

--- Comment #2 from [email protected] ---
A commit in branch main references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=9f5c4ef32812afb4573a278e6eafe5040f839d13

commit 9f5c4ef32812afb4573a278e6eafe5040f839d13
Author:     Konstantin Belousov <[email protected]>
AuthorDate: 2026-07-31 04:12:17 +0000
Commit:     Konstantin Belousov <[email protected]>
CommitDate: 2026-08-07 09:09:50 +0000

    dounmount(9): temporarily enable recursion for the covered vnode lock

    For some complex nullfs mount configurations, it is possible to get the
    covered vnode lock for the mount shared with some inside-mount vnode
    lock.  Then at unmount time, vflush() would recurse on the covered vnode
    lock when reclaiming the vnode.

    Work around it, by temprorarily allowing recursion on the covered vnode
    lock.  Disable recursion after the unmount if it was not enabled before.

    PR:     297174
    Reviewed by:    jah
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D58567

 sys/kern/vfs_mount.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

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