linux-kernel - Re: [PATCH 1/3] rwsem: Implement down_read_killable

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Date:   Thu, 3 Dec 2020 20:58:33 -0500
From:   Waiman Long <longman@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Vasiliy Kulikov <segoon@...nwall.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Christopher Yeoh <cyeoh@....ibm.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Arnd Bergmann <arnd@...db.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 1/3] rwsem: Implement down_read_killable_nested

On 12/3/20 3:10 PM, Eric W. Biederman wrote:
> In preparation for converting exec_update_mutex to a rwsem so that
> multiple readers can execute in parallel and not deadlock, add
> down_read_killable_nested.  This is needed so that kcmp_lock
> can be converted from working on a mutexes to working on rw_semaphores.
>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> ---
>   include/linux/rwsem.h  |  2 ++
>   kernel/locking/rwsem.c | 14 ++++++++++++++
>   2 files changed, 16 insertions(+)
>
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 25e3fde85617..13021b08b2ed 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -171,6 +171,7 @@ extern void downgrade_write(struct rw_semaphore *sem);
>    * See Documentation/locking/lockdep-design.rst for more details.)
>    */
>   extern void down_read_nested(struct rw_semaphore *sem, int subclass);
> +extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass);
>   extern void down_write_nested(struct rw_semaphore *sem, int subclass);
>   extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
>   extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
> @@ -191,6 +192,7 @@ extern void down_read_non_owner(struct rw_semaphore *sem);
>   extern void up_read_non_owner(struct rw_semaphore *sem);
>   #else
>   # define down_read_nested(sem, subclass)		down_read(sem)
> +# define down_read_killable_nested(sem, subclass)	down_read_killable(sem)
>   # define down_write_nest_lock(sem, nest_lock)	down_write(sem)
>   # define down_write_nested(sem, subclass)	down_write(sem)
>   # define down_write_killable_nested(sem, subclass)	down_write_killable(sem)
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index f11b9bd3431d..54d11cb97551 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -1605,6 +1605,20 @@ void down_read_nested(struct rw_semaphore *sem, int subclass)
>   }
>   EXPORT_SYMBOL(down_read_nested);
>   
> +int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
> +{
> +	might_sleep();
> +	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
> +
> +	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
> +		rwsem_release(&sem->dep_map, _RET_IP_);
> +		return -EINTR;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(down_read_killable_nested);
> +
>   void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
>   {
>   	might_sleep();

Acked-by: Waiman Long <longman@...hat.com>

-Longman