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authorThomas Gleixner <tglx@linutronix.de>2021-08-15 23:29:20 +0200
committerIngo Molnar <mingo@kernel.org>2021-08-17 19:06:02 +0200
commit51711e825a6d1b2fe7ca46bb06d08c25d97656ee (patch)
treeffbfd0a341e7715922ad5ce909d5754b8efb5d6c /kernel/locking
parent07d91ef510fb16a2e0ca7453222105835b7ba3b8 (diff)
locking/rtmutex: Prevent lockdep false positive with PI futexes
On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping' and rtmutex based. That causes a lockdep false positive because some of the futex functions invoke spin_unlock(&hb->lock) with the wait_lock of the rtmutex associated to the pi_futex held. spin_unlock() in turn takes wait_lock of the rtmutex on which the spinlock is based which makes lockdep notice a lock recursion. Give the futex/rtmutex wait_lock a separate key. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210815211305.750701219@linutronix.de
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex_api.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c
index 92b7d289a8af..5c9299aaabae 100644
--- a/kernel/locking/rtmutex_api.c
+++ b/kernel/locking/rtmutex_api.c
@@ -214,7 +214,19 @@ EXPORT_SYMBOL_GPL(__rt_mutex_init);
void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,
struct task_struct *proxy_owner)
{
+ static struct lock_class_key pi_futex_key;
+
__rt_mutex_base_init(lock);
+ /*
+ * On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping'
+ * and rtmutex based. That causes a lockdep false positive, because
+ * some of the futex functions invoke spin_unlock(&hb->lock) with
+ * the wait_lock of the rtmutex associated to the pi_futex held.
+ * spin_unlock() in turn takes wait_lock of the rtmutex on which
+ * the spinlock is based, which makes lockdep notice a lock
+ * recursion. Give the futex/rtmutex wait_lock a separate key.
+ */
+ lockdep_set_class(&lock->wait_lock, &pi_futex_key);
rt_mutex_set_owner(lock, proxy_owner);
}