Date: Mon, 22 Jun 2026 11:54:46 +0200
Message-ID: <20260622093321.640886555@kernel.org>
User-Agent: quilt/0.69
From: Thomas Gleixner <tglx@kernel.org>
To: stable@vger.kernel.org
Cc: Waiman Long <longman@redhat.com>,
 Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
 syzbot+b8ca586b9fc235f0c0df@syzkaller.appspotmail.com,
 Helen Koike <koike@igalia.com>
Subject: [patch v6.18.y 3/4] debugobjects: Do not fill_pool() if pi_blocked_on
References: <20260622093040.582177124@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8

From: Helen Koike <koike@igalia.com>

commit 5f41161059fd0f1bbf18c90f3180e38cc45a14eb upstream.

On RT enabled kernels, fill_pool() ends up calling rtlock_lock(), which
asserts if current::pi_blocked_on is set, because a task can obviously only
block on one lock as otherwise the priority inheritenace chain gets
corrupted.

Prevent this by expanding the conditional to take current::pi_blocked_on
into account.

Fixes: 4bedcc28469a ("debugobjects: Make them PREEMPT_RT aware")
Reported-by: syzbot+b8ca586b9fc235f0c0df@syzkaller.appspotmail.com
Signed-off-by: Helen Koike <koike@igalia.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260511215359.3351259-1-koike@igalia.com
Closes: https://syzkaller.appspot.com/bug?extid=b8ca586b9fc235f0c0df
---
 lib/debugobjects.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)
---
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 4343dc5e5c99..cbd025dae5ce 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -711,6 +711,15 @@ static struct debug_obj *lookup_object_or_alloc(void *addr, struct debug_bucket 
 	return NULL;
 }
 
+static inline bool debug_objects_is_pi_blocked_on(void)
+{
+#ifdef CONFIG_RT_MUTEXES
+	return current->pi_blocked_on != NULL;
+#else
+	return false;
+#endif
+}
+
 static void debug_objects_fill_pool(void)
 {
 	if (!static_branch_likely(&obj_cache_enabled))
@@ -727,11 +736,12 @@ static void debug_objects_fill_pool(void)
 
 	/*
 	 * On RT enabled kernels the pool refill must happen in preemptible
-	 * context -- for !RT kernels we rely on the fact that spinlock_t and
-	 * raw_spinlock_t are basically the same type and this lock-type
-	 * inversion works just fine.
+	 * context and not enqueued on an rt_mutex -- for !RT kernels we rely
+	 * on the fact that spinlock_t and raw_spinlock_t are basically the
+	 * same type and this lock-type inversion works just fine.
 	 */
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible() || system_state < SYSTEM_SCHEDULING) {
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || system_state < SYSTEM_SCHEDULING ||
+	    (preemptible() && !debug_objects_is_pi_blocked_on())) {
 		/*
 		 * Annotate away the spinlock_t inside raw_spinlock_t warning
 		 * by temporarily raising the wait-type to LD_WAIT_CONFIG, matching