[PATCH] bcache: fix I/O accounting leak in detached_dev_do_request

[PATCH] bcache: fix I/O accounting leak in detached_dev_do_request

[zhangshida2026]

From: Shida Zhang <zhangshida@kylinos.cn>

When a bcache device is in a detached state, iostat can show 100%
utilization even after I/O workload completion.

This happens because the caller, cached_dev_submit_bio(), calls
bio_start_io_acct() to begin accounting. However, if the bio hits an
early exit path in detached_dev_do_request()—either due to an
unsupported discard request or a bio_alloc_clone() failure—the
corresponding bio_end_io_acct() is never called. This leaves the
in-flight counter permanently incremented, causing the kernel to
report the device as 100% busy.

Add the missing bio_end_io_acct() calls to these error/early-exit
paths to ensure proper I/O accounting.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 drivers/md/bcache/request.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index a02aecac05c..7d855e66a10 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -1107,6 +1107,7 @@ static void detached_dev_do_request(struct bcache_device *d,
 
 	if (bio_op(orig_bio) == REQ_OP_DISCARD &&
 	    !bdev_max_discard_sectors(dc->bdev)) {
+		bio_end_io_acct(orig_bio, start_time);
 		bio_endio(orig_bio);
 		return;
 	}
@@ -1114,6 +1115,7 @@ static void detached_dev_do_request(struct bcache_device *d,
 	clone_bio = bio_alloc_clone(dc->bdev, orig_bio, GFP_NOIO,
 				    &d->bio_detached);
 	if (!clone_bio) {
+		bio_end_io_acct(orig_bio, start_time);
 		orig_bio->bi_status = BLK_STS_RESOURCE;
 		bio_endio(orig_bio);
 		return;
-- 
2.34.1

Re: [PATCH] bcache: fix I/O accounting leak in detached_dev_do_request

[Coly Li]

On Mon, Jan 26, 2026 at 09:42:09AM +0800, zhangshida2026@163.com wrote:
> From: Shida Zhang <zhangshida@kylinos.cn>
> 
> When a bcache device is in a detached state, iostat can show 100%
> utilization even after I/O workload completion.
> 
> This happens because the caller, cached_dev_submit_bio(), calls
> bio_start_io_acct() to begin accounting. However, if the bio hits an
> early exit path in detached_dev_do_request()—either due to an
> unsupported discard request or a bio_alloc_clone() failure—the
> corresponding bio_end_io_acct() is never called. This leaves the
> in-flight counter permanently incremented, causing the kernel to
> report the device as 100% busy.
> 
> Add the missing bio_end_io_acct() calls to these error/early-exit
> paths to ensure proper I/O accounting.
> 
> Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>

Can you mention which patch that this one is fixing? It will help a bit
for downstream maintainers for the backport stuffs.

For this patch, you may add,

Acked-by: Coly Li <colyli@fnnas.com>

Thanks for the fixup.

Coly Li

> ---
>  drivers/md/bcache/request.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index a02aecac05c..7d855e66a10 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -1107,6 +1107,7 @@ static void detached_dev_do_request(struct bcache_device *d,
>  
>  	if (bio_op(orig_bio) == REQ_OP_DISCARD &&
>  	    !bdev_max_discard_sectors(dc->bdev)) {
> +		bio_end_io_acct(orig_bio, start_time);
>  		bio_endio(orig_bio);
>  		return;
>  	}
> @@ -1114,6 +1115,7 @@ static void detached_dev_do_request(struct bcache_device *d,
>  	clone_bio = bio_alloc_clone(dc->bdev, orig_bio, GFP_NOIO,
>  				    &d->bio_detached);
>  	if (!clone_bio) {
> +		bio_end_io_acct(orig_bio, start_time);
>  		orig_bio->bi_status = BLK_STS_RESOURCE;
>  		bio_endio(orig_bio);
>  		return;
> -- 
> 2.34.1
>