[PATCH stable] notifiers: Add oops check in blocking_notifier_call_chain()

[Yi Yang]

In hrtimer_interrupt(), interrupts are disabled when acquiring a spinlock,
which subsequently triggers an oops. During the oops call chain,
blocking_notifier_call_chain() invokes _cond_resched, ultimately leading
to a hard lockup.

Call Stack:
hrtimer_interrupt//raw_spin_lock_irqsave
__hrtimer_run_queues
page_fault
do_page_fault
bad_area_nosemaphore
no_context
oops_end
bust_spinlocks
unblank_screen
do_unblank_screen
fbcon_blank
fb_notifier_call_chain
blocking_notifier_call_chain
down_read
_cond_resched

If the system is in an oops state, use down_read_trylock instead of a
blocking lock acquisition. If the trylock fails, skip executing the
notifier callbacks to avoid potential deadlocks or unsafe operations
during the oops handling process.

Cc: stable@xxxxxxxxxxxxxxx      # 6.6
Fixes: fe9d4f576324 ("Add kernel/notifier.c")
Signed-off-by: Yi Yang <yiyang13@xxxxxxxxxx>
---
 kernel/notifier.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/notifier.c b/kernel/notifier.c
index b3ce28f39eb6..ebff2315fac2 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -384,9 +384,18 @@ int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
 	 * is, we re-check the list after having taken the lock anyway:
 	 */
 	if (rcu_access_pointer(nh->head)) {
-		down_read(&nh->rwsem);
-		ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
-		up_read(&nh->rwsem);
+		if (!oops_in_progress) {
+			down_read(&nh->rwsem);
+			ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
+			up_read(&nh->rwsem);
+		} else {
+			if (down_read_trylock(&nh->rwsem)) {
+				ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
+				up_read(&nh->rwsem);
+			} else {
+				ret = NOTIFY_BAD;
+			}
+		}
 	}
 	return ret;
 }
-- 
2.25.1