Messages in this thread | | | Date | Wed, 10 Sep 2014 07:05:40 +0200 (CEST) | From | Jiri Kosina <> | Subject | Re: [PATCH] mm/sl[aou]b: make kfree() aware of error pointers |
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On Tue, 9 Sep 2014, Andrew Morton wrote:
> > kfree() is happy to accept NULL pointer and does nothing in such case. > > It's reasonable to expect it to behave the same if ERR_PTR is passed to > > it. > > > > Inspired by a9cfcd63e8d ("ext4: avoid trying to kfree an ERR_PTR > > pointer"). > > > > ... > > > > --- a/mm/slab.c > > +++ b/mm/slab.c > > @@ -3612,7 +3612,7 @@ void kfree(const void *objp) > > > > trace_kfree(_RET_IP_, objp); > > > > - if (unlikely(ZERO_OR_NULL_PTR(objp))) > > + if (unlikely(ZERO_OR_NULL_PTR(objp) || IS_ERR(objp))) > > return; > > kfree() is quite a hot path to which this will add overhead. And we > have (as far as we know) no code which will actually use this at > present.
We obviously don't, as such code will be causing explosions. This is meant as a prevention of problems such as the one that has just been fixed in ext4.
> How about a new > > kfree_safe(...) > { > if (IS_ERR(...)) > return; > if (other-stuff-when-we-think-of-it) > return; > kfree(...); > }
I think this unfortunately undermines the whole point of the patch ... if the caller knows that he might potentially be feeding ERR_PTR() to kfree(), he can as well check the pointer himself.
-- Jiri Kosina SUSE Labs
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