Re: [PATCH v8 11/32] vfs: make do_unlinkat retry on ESTALE errors

["J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>]

On Tue, Oct 30, 2012 at 12:33:55PM -0400, Jeff Layton wrote:
> On Tue, 30 Oct 2012 12:14:29 -0400
> "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org> wrote:
> 
> > On Sat, Oct 27, 2012 at 08:33:18AM -0400, Jeff Layton wrote:
> > > Signed-off-by: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > > ---
> > >  fs/namei.c | 12 ++++++++++--
> > >  1 file changed, 10 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/namei.c b/fs/namei.c
> > > index 7c9bb50..467b9f1 100644
> > > --- a/fs/namei.c
> > > +++ b/fs/namei.c
> > > @@ -3446,9 +3446,13 @@ static long do_unlinkat(int dfd, const char __user *pathname)
> > >  	struct filename *name;
> > >  	struct dentry *dentry;
> > >  	struct nameidata nd;
> > > -	struct inode *inode = NULL;
> > > +	struct inode *inode;
> > > +	unsigned int try = 0;
> > > +	unsigned int lookup_flags = LOOKUP_PARENT;
> > >  
> > > -	name = user_path_parent(dfd, pathname, &nd, 0);
> > > +retry:
> > > +	inode = NULL;
> > 
> > So, you fail after "inode" was set (say vfs_unlink returned an error)
> > the first time, then before "inode" was set (lookup_hash returns an
> > error), and you end up incorrectly doing another iput() the second time
> > through if you don't reset inode here?
> > 
> > (I think I made the same mistake in another patch, actually....)
> > 
> > --b.
> > 
> 
> Correct. That's a new delta in this patch, btw. The original patch
> didn't do that and it was causing a busy inodes on umount bug in
> testing.
> 
> It would occasionally hit an ESTALE error in this function and
> because "inode" wasn't reset to NULL, it would do a double-put of the
> inode and cause the counter to underflow.
> 
> It might be good to restructure this code to make those sorts of bugs
> less likely, but the error handling in here is already so hairy that I
> decided to punt on that for now...

Understood.  I might find it just a little more obvious why we're doing
this if the assignment was next to the final iput:

	if (inode)
		iput(inode);
	inode = NULL;
	...

--b.

> 
> > > +	name = user_path_parent(dfd, pathname, &nd, try);
> > >  	if (IS_ERR(name))
> > >  		return PTR_ERR(name);
> > >  
> > > @@ -3486,6 +3490,10 @@ exit2:
> > >  exit1:
> > >  	path_put(&nd.path);
> > >  	putname(name);
> > > +	if (retry_estale(error, try++)) {
> > > +		lookup_flags |= LOOKUP_REVAL;
> > > +		goto retry;
> > > +	}
> > >  	return error;
> > >  
> > >  slashes:
> > > -- 
> > > 1.7.11.7
> > > 
> > > --
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> 
> 
> -- 
> Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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