From 02ea9fc96fe976e7f7e067f38b12202f126e3f2f Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 29 Nov 2021 18:46:46 +0100
Subject: [PATCH] locking/rtmutex: Squash self-deadlock check for ww_rt_mutex.
Git-commit: 02ea9fc96fe976e7f7e067f38b12202f126e3f2f
Patch-mainline: v5.17-rc1
References: bsc#1190137 bsc#1189998
Similar to the issues in commits:
6467822b8cc9 ("locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes")
a055fcc132d4 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")
ww_rt_mutex_lock() should not return EDEADLK without first going through
the __ww_mutex logic to set the required state. In fact, the chain-walk
can deal with the spurious cycles (per the above commits) this check
warns about and is trying to avoid.
Therefore ignore this test for ww_rt_mutex and simply let things fall
in place.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20211129174654.668506-4-bigeasy@linutronix.de
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
kernel/locking/rtmutex.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 0c6a48dfcecb..f89620852774 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1103,8 +1103,11 @@ static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
* the other will detect the deadlock and return -EDEADLOCK,
* which is wrong, as the other waiter is not in a deadlock
* situation.
+ *
+ * Except for ww_mutex, in that case the chain walk must already deal
+ * with spurious cycles, see the comments at [3] and [6].
*/
- if (owner == task)
+ if (owner == task && !(build_ww_mutex() && ww_ctx))
return -EDEADLK;
raw_spin_lock(&task->pi_lock);
--
2.35.1