Re: [PATCH] Btrfs: fix regression in re-setting a large xattr

[Josef Bacik <josef@redhat.com>]

On Fri, Oct 14, 2011 at 09:04:28AM +0900, Tsutomu Itoh wrote:
> (2011/10/14 2:11), Josef Bacik wrote:
> > Recently I changed the xattr stuff to unconditionally set the xattr first in
> > case the xattr didn't exist yet.  This has introduced a regression when setting
> > an xattr that already exists with a large value.  If we find the key we are
> > looking for split_leaf will assume that we're extending that item.  The problem
> > is the size we pass down to btrfs_search_slot includes the size of the item
> > already, so if we have the largest xattr we can possibly have plus the size of
> > the xattr item plus the xattr item that btrfs_search_slot we'd overflow the
> > leaf.  Thankfully this is not what we're doing, but split_leaf doesn't know this
> > so it just returns EOVERFLOW.  So in the xattr code we need to check and see if
> > we got back EOVERFLOW and treat it like EEXIST since that's really what
> > happened.  Thanks,
> > 
> > Signed-off-by: Josef Bacik <josef@redhat.com>
> > ---
> >  fs/btrfs/xattr.c |   13 ++++++++++++-
> >  1 files changed, 12 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> > index 69565e5..5bd7877 100644
> > --- a/fs/btrfs/xattr.c
> > +++ b/fs/btrfs/xattr.c
> > @@ -127,7 +127,18 @@ static int do_setxattr(struct btrfs_trans_handle *trans,
> >  again:
> >  	ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
> >  				      name, name_len, value, size);
> > -	if (ret == -EEXIST) {
> > +	/*
> > +	 * If we're setting an xattr to a new value but the new value is say
> > +	 * exactly BTRFS_MAX_XATTR_SIZE, we could end up with EOVERFLOW getting
> > +	 * back from split_leaf.  This is because it thinks we'll be extending
> > +	 * the existing item size, but we're asking for enough space to add the
> > +	 * item itself.  So if we get EOVERFLOW just set ret to EEXIST and let
> > +	 * the rest of the function figure it out.
> > +	 */
> > +	if (ret == -EOVERFLOW)
> > +		ret = -EEXIST;
> > +
> > +	if (ret == -EEXIST || ret == -EOVERFLOW) {
> 
> Why tested again EOVERFLOW?
> 

Oops thats my fault, I had thought to check for eoverflow but then thought
better to just set it to eexist and didn't fix the first thought.  I'll send out
a fix.  Thanks,

Josef