From 02ea9fc96fe976e7f7e067f38b12202f126e3f2f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 29 Nov 2021 18:46:46 +0100 Subject: locking/rtmutex: Squash self-deadlock check for ww_rt_mutex. 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) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20211129174654.668506-4-bigeasy@linutronix.de --- kernel/locking/rtmutex.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/locking/rtmutex.c') 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); -- cgit v1.2.3 From c0bed69daf4b67809b58cc7cd81a8fa4f45bc161 Mon Sep 17 00:00:00 2001 From: Kefeng Wang Date: Fri, 3 Dec 2021 15:59:34 +0800 Subject: locking: Make owner_on_cpu() into Move the owner_on_cpu() from kernel/locking/rwsem.c into include/linux/sched.h with under CONFIG_SMP, then use it in the mutex/rwsem/rtmutex to simplify the code. Signed-off-by: Kefeng Wang Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20211203075935.136808-2-wangkefeng.wang@huawei.com --- include/linux/sched.h | 9 +++++++++ kernel/locking/mutex.c | 11 ++--------- kernel/locking/rtmutex.c | 5 ++--- kernel/locking/rwsem.c | 9 --------- 4 files changed, 13 insertions(+), 21 deletions(-) (limited to 'kernel/locking/rtmutex.c') diff --git a/include/linux/sched.h b/include/linux/sched.h index 78c351e35fec..ff609d9c2f21 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2171,6 +2171,15 @@ extern long sched_getaffinity(pid_t pid, struct cpumask *mask); #endif #ifdef CONFIG_SMP +static inline bool owner_on_cpu(struct task_struct *owner) +{ + /* + * As lock holder preemption issue, we both skip spinning if + * task is not on cpu or its cpu is preempted + */ + return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); +} + /* Returns effective CPU energy utilization, as seen by the scheduler */ unsigned long sched_cpu_util(int cpu, unsigned long max); #endif /* CONFIG_SMP */ diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index db1913611192..5e3585950ec8 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -367,8 +367,7 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner, /* * Use vcpu_is_preempted to detect lock holder preemption issue. */ - if (!owner->on_cpu || need_resched() || - vcpu_is_preempted(task_cpu(owner))) { + if (!owner_on_cpu(owner) || need_resched()) { ret = false; break; } @@ -403,14 +402,8 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock) * structure won't go away during the spinning period. */ owner = __mutex_owner(lock); - - /* - * As lock holder preemption issue, we both skip spinning if task is not - * on cpu or its cpu is preempted - */ - if (owner) - retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); + retval = owner_on_cpu(owner); /* * If lock->owner is not set, the mutex has been released. Return true diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index f89620852774..0c1f2e3f019a 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1382,9 +1382,8 @@ static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, * for CONFIG_PREEMPT_RCU=y) * - the VCPU on which owner runs is preempted */ - if (!owner->on_cpu || need_resched() || - rt_mutex_waiter_is_top_waiter(lock, waiter) || - vcpu_is_preempted(task_cpu(owner))) { + if (!owner_on_cpu(owner) || need_resched() || + rt_mutex_waiter_is_top_waiter(lock, waiter)) { res = false; break; } diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index c51387a43265..b92d0a830568 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -613,15 +613,6 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) return false; } -static inline bool owner_on_cpu(struct task_struct *owner) -{ - /* - * As lock holder preemption issue, we both skip spinning if - * task is not on cpu or its cpu is preempted - */ - return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); -} - static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner; -- cgit v1.2.3