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Date: Thu, 13 Oct 2022 00:30:02 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: "Connor O'Brien" <connoro@...gle.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
John Stultz <jstultz@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
Qais Yousef <qais.yousef@....com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [RFC PATCH 04/11] locking/mutex: make mutex::wait_lock irq safe
On Mon, Oct 3, 2022 at 5:45 PM Connor O'Brien <connoro@...gle.com> wrote:
>
> From: Juri Lelli <juri.lelli@...hat.com>
>
> mutex::wait_lock might be nested under rq->lock.
>
> Make it irq safe then.
Hi Juri, can you give an example where not doing this is an issue?
When nested under rq->lock, interrupts should already be disabled,
otherwise try_to_wake_up() from an interrupt can cause a deadlock no?
Then, why do you need this patch?
Thanks.
> Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/20181009092434.26221-7-juri.lelli@redhat.com
> [rebase & fix {un,}lock_wait_lock helpers in ww_mutex.h]
> Signed-off-by: Connor O'Brien <connoro@...gle.com>
> ---
> kernel/locking/mutex.c | 18 ++++++++++--------
> kernel/locking/ww_mutex.h | 22 ++++++++++++----------
> 2 files changed, 22 insertions(+), 18 deletions(-)
>
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index 7800380219db..f39e9ee3c4d0 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -572,6 +572,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> {
> struct mutex_waiter waiter;
> struct ww_mutex *ww;
> + unsigned long flags;
> int ret;
>
> if (!use_ww_ctx)
> @@ -614,7 +615,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> return 0;
> }
>
> - raw_spin_lock(&lock->wait_lock);
> + raw_spin_lock_irqsave(&lock->wait_lock, flags);
> /*
> * After waiting to acquire the wait_lock, try again.
> */
> @@ -676,7 +677,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> goto err;
> }
>
> - raw_spin_unlock(&lock->wait_lock);
> + raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> if (ww_ctx)
> ww_ctx_wake(ww_ctx);
> schedule_preempt_disabled();
> @@ -703,9 +704,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> trace_contention_begin(lock, LCB_F_MUTEX);
> }
>
> - raw_spin_lock(&lock->wait_lock);
> + raw_spin_lock_irqsave(&lock->wait_lock, flags);
> }
> - raw_spin_lock(&lock->wait_lock);
> + raw_spin_lock_irqsave(&lock->wait_lock, flags);
> acquired:
> __set_current_state(TASK_RUNNING);
>
> @@ -732,7 +733,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> if (ww_ctx)
> ww_mutex_lock_acquired(ww, ww_ctx);
>
> - raw_spin_unlock(&lock->wait_lock);
> + raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> if (ww_ctx)
> ww_ctx_wake(ww_ctx);
> preempt_enable();
> @@ -743,7 +744,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
> __mutex_remove_waiter(lock, &waiter);
> err_early_kill:
> trace_contention_end(lock, ret);
> - raw_spin_unlock(&lock->wait_lock);
> + raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> debug_mutex_free_waiter(&waiter);
> mutex_release(&lock->dep_map, ip);
> if (ww_ctx)
> @@ -915,6 +916,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
> struct task_struct *next = NULL;
> DEFINE_WAKE_Q(wake_q);
> unsigned long owner;
> + unsigned long flags;
>
> mutex_release(&lock->dep_map, ip);
>
> @@ -941,7 +943,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
> }
> }
>
> - raw_spin_lock(&lock->wait_lock);
> + raw_spin_lock_irqsave(&lock->wait_lock, flags);
> debug_mutex_unlock(lock);
> if (!list_empty(&lock->wait_list)) {
> /* get the first entry from the wait-list: */
> @@ -959,7 +961,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
> __mutex_handoff(lock, next);
>
> preempt_disable();
> - raw_spin_unlock(&lock->wait_lock);
> + raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
>
> wake_up_q(&wake_q);
> preempt_enable();
> diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h
> index dfc174cd96c6..7edd55d10f87 100644
> --- a/kernel/locking/ww_mutex.h
> +++ b/kernel/locking/ww_mutex.h
> @@ -70,14 +70,14 @@ __ww_mutex_has_waiters(struct mutex *lock)
> return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
> }
>
> -static inline void lock_wait_lock(struct mutex *lock)
> +static inline void lock_wait_lock(struct mutex *lock, unsigned long *flags)
> {
> - raw_spin_lock(&lock->wait_lock);
> + raw_spin_lock_irqsave(&lock->wait_lock, *flags);
> }
>
> -static inline void unlock_wait_lock(struct mutex *lock)
> +static inline void unlock_wait_lock(struct mutex *lock, unsigned long flags)
> {
> - raw_spin_unlock(&lock->wait_lock);
> + raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
> }
>
> static inline void lockdep_assert_wait_lock_held(struct mutex *lock)
> @@ -144,14 +144,14 @@ __ww_mutex_has_waiters(struct rt_mutex *lock)
> return rt_mutex_has_waiters(&lock->rtmutex);
> }
>
> -static inline void lock_wait_lock(struct rt_mutex *lock)
> +static inline void lock_wait_lock(struct rt_mutex *lock, unsigned long *flags)
> {
> - raw_spin_lock(&lock->rtmutex.wait_lock);
> + raw_spin_lock_irqsave(&lock->rtmutex.wait_lock, *flags);
> }
>
> -static inline void unlock_wait_lock(struct rt_mutex *lock)
> +static inline void unlock_wait_lock(struct rt_mutex *lock, flags)
> {
> - raw_spin_unlock(&lock->rtmutex.wait_lock);
> + raw_spin_unlock_irqrestore(&lock->rtmutex.wait_lock, flags);
> }
>
> static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
> @@ -382,6 +382,8 @@ __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
> static __always_inline void
> ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> {
> + unsigned long flags;
> +
> ww_mutex_lock_acquired(lock, ctx);
>
> /*
> @@ -409,9 +411,9 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> * Uh oh, we raced in fastpath, check if any of the waiters need to
> * die or wound us.
> */
> - lock_wait_lock(&lock->base);
> + lock_wait_lock(&lock->base, &flags);
> __ww_mutex_check_waiters(&lock->base, ctx);
> - unlock_wait_lock(&lock->base);
> + unlock_wait_lock(&lock->base, flags);
> }
>
> static __always_inline int
> --
> 2.38.0.rc1.362.ged0d419d3c-goog
>
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