Re: [PATCH] slab: fix memory leak when refill_sheaf() fails

[Harry Yoo]

On Wed, Mar 11, 2026 at 05:54:40PM +0100, Vlastimil Babka wrote:
> On 3/11/26 17:30, Hao Li wrote:
> >> 
> >> I also want to bring up another point here, although it may be outside the
> >> scope of the current fix.
> >> 
> >> When I looked into the refill_sheaf() path, I found a refill failure does not
> >> guarantee that the sheaf remains intact: refill_sheaf() can partially fill the
> >> sheaf before failing. This non-intact behavior propagates to its caller,
> >> __prefill_sheaf_pfmemalloc(), which therefore also cannot assume that the sheaf
> >> is still intact after a refill failure.
> >> 
> >> However, the comment for kmem_cache_refill_sheaf() says that "if the refill
> >> fails (returning -ENOMEM), the existing sheaf is left intact." That means the
> >> behavior of __prefill_sheaf_pfmemalloc() - where the sheaf may be left
> >> partially filled on refill failure - contradicts the API contract of
> >> kmem_cache_refill_sheaf().
> >> 
> >> Maybe we can add rollback logic to __prefill_sheaf_pfmemalloc() so that it
> >> provides intact semantics, preventing the non-intact behavior of refill_sheaf()
> >> from propagating up to kmem_cache_refill_sheaf().
> > 
> > Looking at this a bit more, after checking the current callers, it seems that
> > the existing callers of kmem_cache_refill_sheaf() are not relying on the sheaf
> > remaining intact on refill failure.
> > 
> > If so, then another possible option might be to update the comment for
> > kmem_cache_refill_sheaf() to match the current behavior, rather than adding
> > rollback logic.
> 
> I agree with this option. Having possibly more objects than before the call
> shouldn't be an issue for the callers.

+1 for this!

-- 
Cheers,
Harry / Hyeonggon