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bio: fix kmemleak false positives from percpu bio alloc cache

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When a bio is allocated from the mempool with REQ_ALLOC_CACHE set and
later completed, bio_put() places it into the per-cpu bio_alloc_cache
via bio_put_percpu_cache() instead of freeing it back to the
mempool/slab. The slab allocation remains tracked by kmemleak, but the
only reference to the bio is through the percpu cache's free_list,
which kmemleak fails to trace through percpu memory. This causes
kmemleak to report the cached bios as unreferenced objects.

Use symmetric kmemleak_free()/kmemleak_alloc() calls to properly track
bios across percpu cache transitions:

 - bio_put_percpu_cache: call kmemleak_free() when a bio enters the
   cache, unregistering it from kmemleak tracking.

 - bio_alloc_percpu_cache: call kmemleak_alloc() when a bio is taken
   from the cache for reuse, re-registering it so that genuine leaks
   of reused bios remain detectable.

 - __bio_alloc_cache_prune: call kmemleak_alloc() before bio_free() so
   that kmem_cache_free()'s internal kmemleak_free() has a matching
   allocation to pair with.

Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260326144058.2392319-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei
2026-04-02 07:07:03 -06:00
committed by Jens Axboe
parent f91ffe89b2
commit c691e4b0d8
1 changed files with 14 additions and 0 deletions
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block/bio.c
+14
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@@ -18,6 +18,7 @@
#include <linux/highmem.h>
#include <linux/blk-crypto.h>
#include <linux/xarray.h>
#include <linux/kmemleak.h>
#include <trace/events/block.h>
#include "blk.h"
@@ -116,6 +117,11 @@ static inline unsigned int bs_bio_slab_size(struct bio_set *bs)
return bs->front_pad + sizeof(struct bio) + bs->back_pad;
}
static inline void *bio_slab_addr(struct bio *bio)
{
return (void *)bio - bio->bi_pool->front_pad;
}
static struct kmem_cache *bio_find_or_create_slab(struct bio_set *bs)
{
unsigned int size = bs_bio_slab_size(bs);
@@ -486,6 +492,9 @@ static struct bio *bio_alloc_percpu_cache(struct bio_set *bs)
cache->nr--;
put_cpu();
bio->bi_pool = bs;
kmemleak_alloc(bio_slab_addr(bio),
kmem_cache_size(bs->bio_slab), 1, GFP_NOIO);
return bio;
}
@@ -728,6 +737,9 @@ static int __bio_alloc_cache_prune(struct bio_alloc_cache *cache,
while ((bio = cache->free_list) != NULL) {
cache->free_list = bio->bi_next;
cache->nr--;
kmemleak_alloc(bio_slab_addr(bio),
kmem_cache_size(bio->bi_pool->bio_slab),
1, GFP_KERNEL);
bio_free(bio);
if (++i == nr)
break;
@@ -791,6 +803,7 @@ static inline void bio_put_percpu_cache(struct bio *bio)
bio->bi_bdev = NULL;
cache->free_list = bio;
cache->nr++;
kmemleak_free(bio_slab_addr(bio));
} else if (in_hardirq()) {
lockdep_assert_irqs_disabled();
@@ -798,6 +811,7 @@ static inline void bio_put_percpu_cache(struct bio *bio)
bio->bi_next = cache->free_list_irq;
cache->free_list_irq = bio;
cache->nr_irq++;
kmemleak_free(bio_slab_addr(bio));
} else {
goto out_free;
}