linux-kernel - Re: [PATCH 2/3] rwsem: Implement down_read

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Date:   Mon, 7 Dec 2020 10:33:52 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.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 2/3] rwsem: Implement down_read_interruptible

On 12/7/20 4:02 AM, Peter Zijlstra wrote:
> On Thu, Dec 03, 2020 at 08:59:13PM -0500, Waiman Long wrote:
>> On 12/3/20 3:11 PM, Eric W. Biederman wrote:
>>> +static inline int __down_read_interruptible(struct rw_semaphore *sem)
>>> +{
>>> +	if (!rwsem_read_trylock(sem)) {
>>> +		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
>>> +			return -EINTR;
>>> +		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
>>> +	} else {
>>> +		rwsem_set_reader_owned(sem);
>>> +	}
>>> +	return 0;
>>> +}
>>> +
>>>    static inline int __down_read_killable(struct rw_semaphore *sem)
>>>    {
>>>    	if (!rwsem_read_trylock(sem)) {
>>> @@ -1495,6 +1507,20 @@ void __sched down_read(struct rw_semaphore *sem)
>>>    }
>>>    EXPORT_SYMBOL(down_read);
>>> +int __sched down_read_interruptible(struct rw_semaphore *sem)
>>> +{
>>> +	might_sleep();
>>> +	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
>>> +
>>> +	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
>>> +		rwsem_release(&sem->dep_map, _RET_IP_);
>>> +		return -EINTR;
>>> +	}
>>> +
>>> +	return 0;
>>> +}
>>> +EXPORT_SYMBOL(down_read_interruptible);
>>> +
>>>    int __sched down_read_killable(struct rw_semaphore *sem)
>>>    {
>>>    	might_sleep();
>> Acked-by: Waiman Long <longman@...hat.com>
> Yeah, that seems correct.. There's an unfortunate amount of copy-paste
> there though.
>
> Do we want to follow that up with something like this?

I am actually thinking about similar streamlining once the patch lands.

Your suggested changes look fine to me.

Cheers,
Longman