[PATCH] buffer: fix kmemleak false positive in submit_bh_wbc

[Sasha Levin <sashal@kernel.org>]

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@kernel.org>
---
 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);
 
-- 
2.51.0