Re: [PATCH] buffer: fix kmemleak false positive in submit_bh_wbc

[Jens Axboe]

On 2/24/26 12:06 PM, Sasha Levin wrote:
> Bios allocated in submit_bh_wbc are properly freed via their end_io
> handler. Since commit 48f22f80938d, bio_put() caches them in a per-CPU
> bio cache for reuse rather than freeing them back to the mempool.
> While cached bios are reachable by kmemleak via the per-CPU cache
> pointers, once recycled for new I/O they are only referenced by block
> layer internals that kmemleak does not scan, causing false positive
> leak reports.
> 
> Mark the bio allocation with kmemleak_not_leak() to suppress the false
> positive.
> 
> Fixes: 48f22f80938d ("block: enable per-cpu bio cache by default")
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  fs/buffer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 22b43642ba574..c298df6c7f8c6 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -49,6 +49,7 @@
>  #include <linux/sched/mm.h>
>  #include <trace/events/block.h>
>  #include <linux/fscrypt.h>
> +#include <linux/kmemleak.h>
>  #include <linux/fsverity.h>
>  #include <linux/sched/isolation.h>
>  
> @@ -2799,6 +2800,7 @@ static void submit_bh_wbc(blk_opf_t opf, struct buffer_head *bh,
>  		opf |= REQ_PRIO;
>  
>  	bio = bio_alloc(bh->b_bdev, 1, opf, GFP_NOIO);
> +	kmemleak_not_leak(bio);
>  
>  	fscrypt_set_bio_crypt_ctx_bh(bio, bh, GFP_NOIO);

What if they do end up getting leaked? This seems like an odd
work-around, would be better to ensure the caching side marks them as
in-use when grabbed and freed when put.

-- 
Jens Axboe