The following commit has been merged into the locking/core branch of tip: Commit-ID: 51711e825a6d1b2fe7ca46bb06d08c25d97656ee Gitweb: https://git.kernel.org/tip/51711e825a6d1b2fe7ca46bb06d08c25d97656ee Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Sun, 15 Aug 2021 23:29:20 +02:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Tue, 17 Aug 2021 19:06:02 +02:00 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@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210815211305.750701219@xxxxxxxxxxxxx --- kernel/locking/rtmutex_api.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c index 92b7d28..5c9299a 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); }
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