Re: Possibly bug in radix_tree_delete, and fix.

[Nick Piggin]

Neil Brown wrote:
> Hi Nick,
>  I believe there is a bug in radix_tree_delete introduced by:
>
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=d5274261ea46f0aae93820fe36628249120d2f75
>
> The nature of the bug is that if a tag is set on a node that is being
> deleted, then that tag is unconditionally cleared in the parent of the
> node, even if the deleted node has siblings with the tag still set.
>
> I don't know what the large-scale consequences of this bug might be,
> but I'm kinda hoping fixing it will fix a nasty NFS client related
> oops we are seeing in radix_tree_tag_set ....

I think you're right. I was kind of suspecting I might have introduced
a silly bug somewhere after a couple of radix tree oopses popped up.

Not sure why it didn't trigger Andrew's test suite, but I guess that's
something to add.

> My suggested patch is below.
>
> Please review, confirm, and Ack:

It should be basically an identical block to the one below in the main
loop, yeah? You're missing the nr_cleared_tags bit.

Something like:

   tags[tag] = 1;
   if (tag_get(pathp->node, tag, pathp->offset)) {
      tag_clear(pathp->node, tag, pathp->offset);
      if (!any_tag_set(pathp->node, tag)) {
         tags[tag] = 0;
         nr_cleared_tags++;
      }
   }

And you can add an
Acked-by: Nick Piggin <npiggin@xxxxxxx>

Thanks,
Nick

> Thanks,
> NeilBrown
>
>
> Fix over-zealous clearing of tags in radix_tree_delete.
>
> Signed-off-by: Neil Brown <neilb@xxxxxxx>
>
> ### Diffstat output
>  ./lib/radix-tree.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff ./lib/radix-tree.c~current~ ./lib/radix-tree.c
> --- ./lib/radix-tree.c~current~	2006-02-16 13:22:28.000000000 +1100
> +++ ./lib/radix-tree.c	2006-02-16 13:23:19.000000000 +1100
> @@ -755,7 +755,7 @@ void *radix_tree_delete(struct radix_tre
>  	for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
>  		if (tag_get(pathp->node, tag, pathp->offset)) {
>  			tag_clear(pathp->node, tag, pathp->offset);
> -			tags[tag] = 0;
> +			tags[tag] = any_tag_set(pathp->node, tag);
>  			nr_cleared_tags++;
>  		} else
>  			tags[tag] = 1;


--
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