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

[Jeff Layton]

On Tue, 30 Oct 2012 12:14:29 -0400
"J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:

> On Sat, Oct 27, 2012 at 08:33:18AM -0400, Jeff Layton wrote:
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> >  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...

> > +	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@xxxxxxxxxx>
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