[PATCH 6.1.y] debugobjects: Do not fill_pool() if pi_blocked_on

[Sasha Levin <sashal@kernel.org>]

From: Helen Koike <koike@igalia.com>

[ Upstream commit 5f41161059fd0f1bbf18c90f3180e38cc45a14eb ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 lib/debugobjects.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 8c3b483a8fb44a..f9d53a0af4238f 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -597,13 +597,23 @@ 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)
 {
 	/*
 	 * On RT enabled kernels the pool refill must happen in preemptible
-	 * context:
+	 * context and not enqueued on an rt_mutex:
 	 */
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible())
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) ||
+	    (preemptible() && !debug_objects_is_pi_blocked_on()))
 		fill_pool();
 }
 
-- 
2.53.0