Subject: Re: [Patch] pipe: use file_update_time() when hold i_mutex
From: Miklos Szeredi <mszeredi@suse.cz>
To: Amerigo Wang <amwang@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       heiko.carstens@de.ibm.com, linux-fsdevel@vger.kernel.org,
       viro@zeniv.linux.org.uk
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	 <20090720141150.e9d081ca.akpm@linux-foundation.org>
	 <4A65934B.9050904@redhat.com>
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Date: Tue, 21 Jul 2009 13:09:40 +0200
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On Tue, 2009-07-21 at 18:07 +0800, Amerigo Wang wrote:
> Andrew Morton wrote:
> > On Mon, 6 Jul 2009 01:35:30 -0400
> > Amerigo Wang <amwang@redhat.com> wrote:
> >
> >   
> >> file_update_time() should be called with i_mutex held,
> >> move it before mutex_unlock().
> >>
> >>     
> >
> > Why do you believe that file_update_time() needs i_mutex?
> >   
> file_update_time() modifies inode, no? :)

So does touch_atime(), yet neither needs i_mutex.

But calling file_update_time() within the locked region in pipe_write()
might make sense regardless: that way a task waiting for data would be
guaranteed to see the time change after receiving a POLLIN event for
example.

Thanks,
Miklos


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