linux-kernel - Re: [PATCH] locking/rwsem: Add up_write_non_owner() for percpu_up

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Date:   Wed, 4 Apr 2018 10:40:09 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] locking/rwsem: Add up_write_non_owner() for
 percpu_up_write()

On 04/04/2018 10:37 AM, Waiman Long wrote:
> The commit 8c5db92a705d ("locking/rwsem: Add DEBUG_RWSEMS to look for
> lock/unlock mismatches") causes a warning in ext4 fstests due to the
> fact that the freeze and thaw ioctls, by design, are run in different
> processes. This is not a bug in the commit itself. Rather, we need a
> up_write() variant that annotates the fact that it can be called from
> a task different from the one that took the lock.
>
> The new API is up_write_non_owner() and the percpu_up_write() function
> is modified to use it instead of the plain up_write().
>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  include/linux/rwsem.h         |  6 ++++++
>  kernel/locking/percpu-rwsem.c |  4 +++-
>  kernel/locking/rwsem.c        | 13 +++++++++++++
>  3 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 56707d5..0e2a425 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -187,4 +187,10 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
>  # define up_read_non_owner(sem)			up_read(sem)
>  #endif
>  
> +#ifdef CONFIG_DEBUG_RWSEMS
> +extern void up_write_non_owner(struct rw_semaphore *sem);
> +#else
> +# define up_write_non_owner(sem)	up_write(sem)
> +#endif
> +
>  #endif /* _LINUX_RWSEM_H */
> diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
> index 883cf1b..13decf2 100644
> --- a/kernel/locking/percpu-rwsem.c
> +++ b/kernel/locking/percpu-rwsem.c
> @@ -179,8 +179,10 @@ void percpu_up_write(struct percpu_rw_semaphore *sem)
>  
>  	/*
>  	 * Release the write lock, this will allow readers back in the game.
> +	 * percpu_up_write() may be called from a task different from the one
> +	 * taking the lock.
>  	 */
> -	up_write(&sem->rw_sem);
> +	up_write_non_owner(&sem->rw_sem);
>  
>  	/*
>  	 * Once this completes (at least one RCU-sched grace period hence) the
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index 30465a2..140d5ef 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -222,4 +222,17 @@ void up_read_non_owner(struct rw_semaphore *sem)
>  
>  #endif
>  
> +#ifdef CONFIG_DEBUG_RWSEMS
> +/*
> + * release a write lock from a different task
> + */
> +void up_write_non_owner(struct rw_semaphore *sem)
> +{
> +	rwsem_release(&sem->dep_map, 1, _RET_IP_);
> +	DEBUG_RWSEMS_WARN_ON(!sem->owner || (sem->owner == RWSEM_READER_OWNED));
>  
> +	rwsem_clear_owner(sem);
> +	__up_write(sem);
> +}
> +EXPORT_SYMBOL(up_write_non_owner);
> +#endif

Theodore,

Could you try this patch to see if it can fix your fstests warning?

Thanks,
Longman