Re: missing mnt_drop_write() on open error

From: Miklos Szeredi
Date: Wed Sep 26 2007 - 13:53:20 EST

> 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-> 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.

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