linux-kernel - Re: [PATCH 2/2][RFC][BUG] msync: updating ctime and mtime at syncing

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Message-Id: <1200143342.7999.25.camel@lappy>
Date:	Sat, 12 Jan 2008 14:09:01 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Anton Salikhmetov <salikhmetov@...il.com>
Cc:	linux-mm@...ck.org, jakob@...hought.net,
	linux-kernel@...r.kernel.org, Valdis.Kletnieks@...edu,
	riel@...hat.com, ksm@...dk, staubach@...hat.com,
	jesper.juhl@...il.com
Subject: Re: [PATCH 2/2][RFC][BUG] msync: updating ctime and mtime at
	syncing


On Sat, 2008-01-12 at 15:38 +0300, Anton Salikhmetov wrote:
> 2008/1/12, Peter Zijlstra <a.p.zijlstra@...llo.nl>:
> >
> > On Sat, 2008-01-12 at 10:36 +0100, Peter Zijlstra wrote:
> > > On Fri, 2008-01-11 at 03:44 +0300, Anton Salikhmetov wrote:
> > >
> > > > +/*
> > > > + * Update the ctime and mtime stamps after checking if they are to be updated.
> > > > + */
> > > > +void mapped_file_update_time(struct file *file)
> > > > +{
> > > > +   if (test_and_clear_bit(AS_MCTIME, &file->f_mapping->flags)) {
> > > > +           get_file(file);
> > > > +           file_update_time(file);
> > > > +           fput(file);
> > > > +   }
> > > > +}
> > > > +
> > >
> > > I don't think you need the get/put file stuff here, because
> >
> > BTW, the reason for me noticing this is that if it would be needed there
> > is a race condition right there, who is to say that the file pointer
> > you're deref'ing in your test condition isn't a dead one already.
> 
> So, in your opinion, is it at all needed here to play with the file reference
> counter? May I drop the get_file() and fput() calls from the
> sys_msync() function?

No, the ones in sys_msync() around calling do_fsync() are most
definately needed because we release mmap_sem there.

What I'm saying is that you can remove the get_file()/fput() calls from
your new mapped_file_update_time() function.

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