From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
Oleg Nesterov <oleg@redhat.com>,
Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag
Date: Tue, 15 May 2018 19:55:14 +0200 [thread overview]
Message-ID: <20180515175514.GM12217@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <4d823d09-b41c-2f86-40b7-f110bf30afd8@redhat.com>
On Tue, May 15, 2018 at 01:52:06PM -0400, Waiman Long wrote:
> On 05/15/2018 01:48 PM, Peter Zijlstra wrote:
> > On Tue, May 15, 2018 at 01:38:03PM -0400, Waiman Long wrote:
> >> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> >> index 30465a2..b7208e1 100644
> >> --- a/kernel/locking/rwsem.c
> >> +++ b/kernel/locking/rwsem.c
> >> @@ -130,7 +130,8 @@ void up_read(struct rw_semaphore *sem)
> >> void up_write(struct rw_semaphore *sem)
> >> {
> >> rwsem_release(&sem->dep_map, 1, _RET_IP_);
> >> - DEBUG_RWSEMS_WARN_ON(sem->owner != current);
> >> + DEBUG_RWSEMS_WARN_ON((sem->owner != current) &&
> >> + !rwsem_has_anonymous_owner(sem->owner));
> > Why? Don't we always do percpu_rwsem_acquire() before up?
> >
>
> This is to allow an unlock to happen in the unknown owner state. Yes, it
> is not necessary to fix the percpu-rwsem problem. It is there just in
> case a rwsem will be released in that state in the future.
Let's not allow that until there's a very good reason for it.
next prev parent reply other threads:[~2018-05-15 17:55 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-15 17:38 [PATCH v3 0/2] locking/rwsem: Fix DEBUG_RWSEM warning from thaw_super() Waiman Long
2018-05-15 17:38 ` [PATCH v3 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag Waiman Long
2018-05-15 17:46 ` Peter Zijlstra
2018-05-15 17:48 ` Waiman Long
2018-05-15 17:48 ` Peter Zijlstra
2018-05-15 17:52 ` Waiman Long
2018-05-15 17:55 ` Peter Zijlstra [this message]
2018-05-15 17:56 ` Waiman Long
2018-05-15 18:02 ` Peter Zijlstra
2018-05-15 17:38 ` [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN Waiman Long
2018-05-15 17:58 ` Peter Zijlstra
2018-05-15 18:02 ` Waiman Long
2018-05-15 18:05 ` Amir Goldstein
2018-05-15 18:45 ` Waiman Long
2018-05-15 18:05 ` Peter Zijlstra
2018-05-15 18:35 ` Waiman Long
2018-05-15 18:02 ` Matthew Wilcox
2018-05-15 18:07 ` Peter Zijlstra
2018-05-15 18:45 ` Waiman Long
2018-05-15 21:21 ` Matthew Wilcox
2018-05-15 21:30 ` Waiman Long
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