[PATCH] block: use put_io_context_active() to disassociate bio from a task

[PATCH] block: use put_io_context_active() to disassociate bio from a task

[Hou Tao]

bio_associate_current() invokes get_io_context_active() to tell
CFQ scheduler that the current io_context is still issuing IOs
by increasing active_ref. When the bio is done, we also need
to invoke put_io_context_active() to decrease active_ref else
the associated io_context will always be active.

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 5eec5e0..d8ed36f 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2072,7 +2072,7 @@ EXPORT_SYMBOL_GPL(bio_associate_current);
 void bio_disassociate_task(struct bio *bio)
 {
 	if (bio->bi_ioc) {
-		put_io_context(bio->bi_ioc);
+		put_io_context_active(bio->bi_ioc);
 		bio->bi_ioc = NULL;
 	}
 	if (bio->bi_css) {
-- 
2.5.0

Re: [PATCH] block: use put_io_context_active() to disassociate bio from a task

[Tejun Heo]

Hello,

On Fri, Mar 03, 2017 at 03:01:10PM +0800, Hou Tao wrote:
> bio_associate_current() invokes get_io_context_active() to tell
> CFQ scheduler that the current io_context is still issuing IOs
> by increasing active_ref. When the bio is done, we also need
> to invoke put_io_context_active() to decrease active_ref else
> the associated io_context will always be active.
> 
> Signed-off-by: Hou Tao <houtao1@huawei.com>

Can you please explain how you noticed issue and verified the patch?
Also, the patch will need the following.

 Fixes: 852c788f8365 ("block: implement bio_associate_current()")
 Cc: stable@vger.kernel.org # v3.5+

I think the failure mode isn't severe.  We'll be carrying around ioc's
longer than necessary but that's about it.  I wonder whether the logic
can be simplified in general.  Anyways, please feel free to add

 Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun