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

To: Andreas Dilger <adilger@xxxxxxxxx>
Subject: Re: [PATCH 1/4] fs: Improve filesystem freezing handling
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 12 Jan 2012 21:07:53 +0100
Cc: Jan Kara <jack@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, Surbhi Palande <csurbhi@xxxxxxxxx>, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
In-reply-to: <DB1320A4-7621-44D2-B339-78CB38FAC186@xxxxxxxxx>
References: <1326331253-6497-1-git-send-email-jack@xxxxxxx> <1326331253-6497-2-git-send-email-jack@xxxxxxx> <DB1320A4-7621-44D2-B339-78CB38FAC186@xxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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@xxxxxxx>
SUSE Labs, CR

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