linux-kernel - Re: missing mnt_drop

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Message-Id: <E1Iab1W-0005Ye-00@dorka.pomaz.szeredi.hu>
Date:	Wed, 26 Sep 2007 19:50:10 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	haveblue@...ibm.com
CC:	miklos@...redi.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: missing mnt_drop_write() on open error

> On Wed, 2007-09-26 at 10:38 +0200, Miklos Szeredi wrote:
> > In __dentry_open() there's still a few places where fput() won't be
> > called, notably when ->open fails, which is what I'm triggering I
> > think.
> > 
> > Also even more horrible things can happen because of the
> > nd->intent.open.file thing.  For example if the lookup routine calls
> > lookup_instantiate_filp(), and after this, but before may_open() some
> > error happens, then release_open_intent() will call fput() on the
> > file, which will cause mnt_drop_write() to be called, even though a
> > matching mnt_want_write() hasn't yet been called.  Ugly, eh? 
> 
> I'm not sure it is _that_ horrible. ;)
> 
> Do you see any reason we can't just shadow the
> get/put_write_access(inode) calls with mnt_want/drop_write() calls?  I
> think they're always matched.

Maybe.  Can we do the mnt_want_write() from __dentry_open(), instead
of may_open()?  That would be a lot cleaner.

Btw, may_open() doesn't do mnt_want_write() around the truncation if
file is opened with O_TRUNC | O_RDONLY.

Miklos
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