Date: Tue, 25 Nov 2025 14:02:28 +0000 From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 23ddcd227ab7 - stable/15 - kevent: Hold the knlist mutex when invoking f_event(NOTE_FORK) Message-ID: <6925b6f4.2da45.303f61bd@gitrepo.freebsd.org>
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The branch stable/15 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=23ddcd227ab71b1d687f9ea298696f7d082c9cd5 commit 23ddcd227ab71b1d687f9ea298696f7d082c9cd5 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2025-11-18 14:22:04 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2025-11-25 14:02:20 +0000 kevent: Hold the knlist mutex when invoking f_event(NOTE_FORK) In general f_event is supposed to be called with the knlist mutex held, so lock it earlier to follow this protocol. Also make sure that the update to kn_fflags is synchronized. Lock the kqueue itself earlier in the case where the knote is activated, to avoid locking and unlocking the kqueue twice. PR: 291005 Reported by: Qiu-ji Chen <chenqiuji666@gmail.com> Reviewed by: kib MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D53762 (cherry picked from commit d795c753e262b97a93dc353aa66b858e1b1969d1) --- sys/kern/kern_event.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c index 84af7b264d08..c18bf3b12352 100644 --- a/sys/kern/kern_event.c +++ b/sys/kern/kern_event.c @@ -627,12 +627,20 @@ knote_fork(struct knlist *list, int pid) kev.data = kn->kn_id; /* parent */ kev.udata = kn->kn_kevent.udata;/* preserve udata */ error = kqueue_register(kq, &kev, NULL, M_NOWAIT); + + /* + * Serialize updates to the kn_kevent fields with threads + * scanning the queue. + */ + list->kl_lock(list->kl_lockarg); if (error) kn->kn_fflags |= NOTE_TRACKERR; - if (kn->kn_fop->f_event(kn, NOTE_FORK)) - KNOTE_ACTIVATE(kn, 0); - list->kl_lock(list->kl_lockarg); - KQ_LOCK(kq); + if (kn->kn_fop->f_event(kn, NOTE_FORK)) { + KQ_LOCK(kq); + KNOTE_ACTIVATE(kn, 1); + } else { + KQ_LOCK(kq); + } kn_leave_flux(kn); KQ_UNLOCK_FLUX(kq); }help
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