linux-kernel - Re: [PATCH 1/4] fs: Improve filesystem freezing handling

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Message-ID: <20120112200753.GC8778@quack.suse.cz>
Date:	Thu, 12 Jan 2012 21:07:53 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, Eric Sandeen <sandeen@...deen.net>,
	Dave Chinner <dchinner@...hat.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 1/4] fs: Improve filesystem freezing handling

On Thu 12-01-12 12:53:35, Andreas Dilger wrote:
> On 2012-01-11, at 6:20 PM, Jan Kara wrote:
> > /**
> > + * sb_start_write - drop write access to a superblock
> > + * @sb: the super we wrote to
> > + *
> > + * Decrement number of writers to the filesystem and wake up possible
> > + * waiters wanting to freeze the filesystem.
> > + */
> > +void sb_end_write(struct super_block *sb)
> > +{
> > +#ifdef CONFIG_SMP
> > +	this_cpu_dec(sb->s_writers);
> > +#else
> > +	preempt_disable();
> > +	sb->s_writers--;
> > +	preempt_enable();
> > +#endif
> > +	/*
> > +	 * Make sure s_writers are updated before we wake up waiters in
> > +	 * freeze_super().
> > +	 */
> > +	smp_mb();
> > +	if (waitqueue_active(&sb->s_writers_wait))
> > +		wake_up(&sb->s_writers_wait);
> > +	rwsem_release(&sb->s_writers_lock_map, 1, _RET_IP_);
> > +}
> 
> Since this function is needed for calling __block_page_mkwrite(), which is
> EXPORT_SYMBOL(), both sb_start_write() and sb_end_write() themselves need
> to be EXPORT_SYMBOL().
  Good point. Fixed. Thanks.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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