linux-kernel - Re: [PATCH] Remove BKL from fs/locks.c

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Date:	Wed, 15 Sep 2010 11:22:01 -0700 (PDT)
From:	Sage Weil <sage@...dream.net>
To:	Arnd Bergmann <arnd@...db.de>
cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Matthew Wilcox <willy@...ux.intel.com>,
	Christoph Hellwig <hch@....de>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, John Kacur <jkacur@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, gregf@...newdream.net
Subject: Re: [PATCH] Remove BKL from fs/locks.c

On Wed, 15 Sep 2010, Arnd Bergmann wrote:

> On Wednesday 15 September 2010, Sage Weil wrote:
> > > @@ -2362,7 +2362,7 @@ static int encode_caps_cb(struct inode *inode, struct ceph_cap *cap,
> > >       if (recon_state->flock) {
> > >               int num_fcntl_locks, num_flock_locks;
> > >  
> > > -             lock_kernel();
> > > +             lock_flocks();
> > >               ceph_count_locks(inode, &num_fcntl_locks, &num_flock_locks);
> > >               rec.v2.flock_len = (2*sizeof(u32) +
> > >                                   (num_fcntl_locks+num_flock_locks) *
> > > @@ -2373,7 +2373,7 @@ static int encode_caps_cb(struct inode *inode, struct ceph_cap *cap,
> > >                       err = ceph_encode_locks(inode, pagelist,
> > >                                               num_fcntl_locks,
> > >                                               num_flock_locks);
> > > -             unlock_kernel();
> > > +             unlock_flocks();
> > >       }
> > 
> > The Ceph code won't currently behave with lock_flocks() taking a spinlock.  
> > We're preparing a patch to fix that now.  As long as there is a window 
> > between lock_flocks() being defined and the spinlock conversion, I can 
> > send the fix upstream then and avoid any breakage.  Or send the patches 
> > your way to include in your tree, whatever you prefer!
> 
> I'd be happy to just integrate the fix in this patch, or as a separate patch
> in the series.
> 
> I certainly don't want to break any file system in the middle of the series,
> I'm sure we can find a way to do it right.
> 
> What is the problem? I just saw ceph_pagelist_addpage potentially sleeping,
> is that what you are thinking of?

Yeah.  The pagelist code needs to be adjusted to handle preallocation of 
potentially multiple pages.  We'll send the fix your way shortly.

Thanks!
sage


> 
> > > +void unlock_flocks(void)
> > > +{
> > > +     unlock_kernel();
> > > +}
> > 
> > EXPORT_SYMBOL(unlock_flocks); ?
> 
> Right, thanks!
> 
> 	Arnd
> 
> 
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