From: Peter Zijlstra <peterz@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@lst.de>, xfs@oss.sgi.com
Subject: Re: [PATCH, RFC] xfs: remove i_iolock and use i_rwsem in the VFS inode instead
Date: Thu, 8 Sep 2016 08:54:42 +0200 [thread overview]
Message-ID: <20160908065442.GV10138@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20160907214536.GQ30056@dastard>
On Thu, Sep 08, 2016 at 07:45:36AM +1000, Dave Chinner wrote:
> On Mon, Sep 05, 2016 at 05:15:29PM +0200, Christoph Hellwig wrote:
> > Hi Dave,
> >
> > I looked into killing the mrlock and ran into an unexpected problem.
> >
> > Currently mr_writer tracks that there is someone holding a write lock,
> > lockdep on the other hand checks if the calling thread has that lock.
> >
> > While that generally is the right semantic, our hack to offload
> > btree splits to a work item offends lockdep. E.g. this callstack
> > now asserts:
>
> It's a semaphore, not a mutex. Semaphore locking is independent of
> task context, the lock follows the object it protects, not the task
> that took the lock. i.e. Lockdep is wrong to assume the "owner" of a
> rw_sem will not change between lock and unlock.
We've added strict owner semantics to rwsem a long time ago.
If you want the actual semaphore semantics (which we greatly discourage,
because you cannot do validation on it) you should use
{down,up}_read_non_owner().
I'm not sure we've got write_non_owner() variants for this.
Turns out, there really are very few 'semaphore' users.
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next prev parent reply other threads:[~2016-09-08 6:54 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-11 17:10 [PATCH, RFC] xfs: remove i_iolock and use i_rwsem in the VFS inode instead Christoph Hellwig
2016-08-11 21:54 ` Peter Zijlstra
2016-08-18 17:37 ` Christoph Hellwig
2016-08-19 13:27 ` Peter Zijlstra
2016-08-20 6:37 ` Christoph Hellwig
2016-08-22 8:34 ` Peter Zijlstra
2016-09-05 15:12 ` Christoph Hellwig
2016-09-07 7:43 ` Peter Zijlstra
2016-09-08 6:06 ` Ingo Molnar
2016-08-11 23:43 ` Dave Chinner
2016-08-12 2:50 ` Christoph Hellwig
2016-08-12 9:58 ` Dave Chinner
2016-09-05 15:15 ` Christoph Hellwig
2016-09-07 21:45 ` Dave Chinner
2016-09-08 6:54 ` Peter Zijlstra [this message]
2016-09-09 1:06 ` Dave Chinner
2016-09-09 8:21 ` Peter Zijlstra
2016-09-09 8:34 ` Christoph Hellwig
2016-09-11 0:17 ` Dave Chinner
2016-09-13 19:42 ` Peter Zijlstra
2016-09-09 8:33 ` Christoph Hellwig
2016-09-09 8:44 ` Peter Zijlstra
2016-09-09 9:05 ` Christoph Hellwig
2016-09-09 9:51 ` Peter Zijlstra
2016-09-10 16:20 ` Christoph Hellwig
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