git: d02c54533aa4 - stable/15 - kqueue: add some kn_knlist assertions around knlist_(add|remove)

The branch stable/15 has been updated by kevans:

URL: https://cgit.FreeBSD.org/src/commit/?id=d02c54533aa49980ad3e8b984d9af4ec835d9adc

commit d02c54533aa49980ad3e8b984d9af4ec835d9adc
Author:     Kyle Evans <kevans@FreeBSD.org>
AuthorDate: 2026-04-01 22:30:48 +0000
Commit:     Kyle Evans <kevans@FreeBSD.org>
CommitDate: 2026-04-13 03:12:29 +0000

    kqueue: add some kn_knlist assertions around knlist_(add|remove)
    
    We currently assert that kn_status is accurate, but there's more room
    for error.  Neither of these are very likely, but currently we'd blow up
    in SLIST*() macros instead of providing more obvious diagnostics.  It's
    perhaps only worth testing these because knlist_remove() requires
    getting logic across both f_attach() and f_detach() correct.
    
    Reviewed by:    kib, markj
    
    (cherry picked from commit 306c9049c642da6a59a5dc088589605a9aa38b87)
---
 sys/kern/kern_event.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index 2d7df3da58bb..915d34ac1695 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -2619,6 +2619,8 @@ knlist_add(struct knlist *knl, struct knote *kn, int islocked)
 	KASSERT(kn_in_flux(kn), ("knote %p not in flux", kn));
 	KASSERT((kn->kn_status & KN_DETACHED) != 0,
 	    ("knote %p was not detached", kn));
+	KASSERT(kn->kn_knlist == NULL,
+	    ("knote %p was already on knlist %p", kn, kn->kn_knlist));
 	if (!islocked)
 		knl->kl_lock(knl->kl_lockarg);
 	SLIST_INSERT_HEAD(&knl->kl_list, kn, kn_selnext);
@@ -2641,6 +2643,8 @@ knlist_remove_kq(struct knlist *knl, struct knote *kn, int knlislocked,
 	KASSERT(kqislocked || kn_in_flux(kn), ("knote %p not in flux", kn));
 	KASSERT((kn->kn_status & KN_DETACHED) == 0,
 	    ("knote %p was already detached", kn));
+	KASSERT(kn->kn_knlist == knl,
+	    ("knote %p was not on knlist %p", kn, knl));
 	if (!knlislocked)
 		knl->kl_lock(knl->kl_lockarg);
 	SLIST_REMOVE(&knl->kl_list, kn, knote, kn_selnext);