* [PATCH] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
@ 2021-08-11 14:38 Ming Lei
2021-08-11 14:55 ` Keith Busch
0 siblings, 1 reply; 3+ messages in thread
From: Ming Lei @ 2021-08-11 14:38 UTC (permalink / raw)
To: Jens Axboe
Cc: linux-block, Bart Van Assche, Christoph Hellwig, John Garry, Ming Lei
Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
refcount before calling ->fn(), so needn't to grab it one more time
in blk_mq_check_expired().
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 25 +++++++------------------
1 file changed, 7 insertions(+), 18 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d2725f94491d..4d3457d2957f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -917,6 +917,10 @@ void blk_mq_put_rq_ref(struct request *rq)
__blk_mq_free_request(rq);
}
+/*
+ * This request won't be re-allocated because its refcount is held when
+ * calling this callback.
+ */
static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
struct request *rq, void *priv, bool reserved)
{
@@ -930,27 +934,12 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
return true;
/*
- * We have reason to believe the request may be expired. Take a
- * reference on the request to lock this request lifetime into its
- * currently allocated context to prevent it from being reallocated in
- * the event the completion by-passes this timeout handler.
- *
- * If the reference was already released, then the driver beat the
- * timeout handler to posting a natural completion.
- */
- if (!refcount_inc_not_zero(&rq->ref))
- return true;
-
- /*
- * The request is now locked and cannot be reallocated underneath the
- * timeout handler's processing. Re-verify this exact request is truly
- * expired; if it is not expired, then the request was completed and
- * reallocated as a new request.
+ * Re-verify this exact request is truly expired; if it is not expired,
+ * then the request was completed and reallocated as a new request
+ * after returning from blk_mq_check_expired().
*/
if (blk_mq_req_expired(rq, next))
blk_mq_rq_timed_out(rq, reserved);
-
- blk_mq_put_rq_ref(rq);
return true;
}
--
2.31.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 14:38 [PATCH] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
@ 2021-08-11 14:55 ` Keith Busch
2021-08-11 15:10 ` Ming Lei
0 siblings, 1 reply; 3+ messages in thread
From: Keith Busch @ 2021-08-11 14:55 UTC (permalink / raw)
To: Ming Lei
Cc: Jens Axboe, linux-block, Bart Van Assche, Christoph Hellwig, John Garry
On Wed, Aug 11, 2021 at 10:38:38PM +0800, Ming Lei wrote:
> Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
> refcount before calling ->fn(), so needn't to grab it one more time
> in blk_mq_check_expired().
>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-mq.c | 25 +++++++------------------
> 1 file changed, 7 insertions(+), 18 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d2725f94491d..4d3457d2957f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -917,6 +917,10 @@ void blk_mq_put_rq_ref(struct request *rq)
> __blk_mq_free_request(rq);
> }
>
> +/*
> + * This request won't be re-allocated because its refcount is held when
> + * calling this callback.
> + */
> static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> struct request *rq, void *priv, bool reserved)
> {
> @@ -930,27 +934,12 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> return true;
>
> /*
> - * We have reason to believe the request may be expired. Take a
> - * reference on the request to lock this request lifetime into its
> - * currently allocated context to prevent it from being reallocated in
> - * the event the completion by-passes this timeout handler.
> - *
> - * If the reference was already released, then the driver beat the
> - * timeout handler to posting a natural completion.
> - */
> - if (!refcount_inc_not_zero(&rq->ref))
> - return true;
> -
> - /*
> - * The request is now locked and cannot be reallocated underneath the
> - * timeout handler's processing. Re-verify this exact request is truly
> - * expired; if it is not expired, then the request was completed and
> - * reallocated as a new request.
> + * Re-verify this exact request is truly expired; if it is not expired,
> + * then the request was completed and reallocated as a new request
> + * after returning from blk_mq_check_expired().
> */
> if (blk_mq_req_expired(rq, next))
> blk_mq_rq_timed_out(rq, reserved);
There's no need to check expired twice if the iterator is already taking a
reference. I had this double check because I didn't want to penalize normal IO
by preventing it from completing while the timeout handler is running, but it
looks like the current timeout iterator is going to do that anyway.
> -
> - blk_mq_put_rq_ref(rq);
> return true;
> }
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] blk-mq: don't grab rq's refcount in blk_mq_check_expired()
2021-08-11 14:55 ` Keith Busch
@ 2021-08-11 15:10 ` Ming Lei
0 siblings, 0 replies; 3+ messages in thread
From: Ming Lei @ 2021-08-11 15:10 UTC (permalink / raw)
To: Keith Busch
Cc: Jens Axboe, linux-block, Bart Van Assche, Christoph Hellwig, John Garry
On Wed, Aug 11, 2021 at 08:55:25AM -0600, Keith Busch wrote:
> On Wed, Aug 11, 2021 at 10:38:38PM +0800, Ming Lei wrote:
> > Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
> > refcount before calling ->fn(), so needn't to grab it one more time
> > in blk_mq_check_expired().
> >
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> > block/blk-mq.c | 25 +++++++------------------
> > 1 file changed, 7 insertions(+), 18 deletions(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index d2725f94491d..4d3457d2957f 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -917,6 +917,10 @@ void blk_mq_put_rq_ref(struct request *rq)
> > __blk_mq_free_request(rq);
> > }
> >
> > +/*
> > + * This request won't be re-allocated because its refcount is held when
> > + * calling this callback.
> > + */
> > static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> > struct request *rq, void *priv, bool reserved)
> > {
> > @@ -930,27 +934,12 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> > return true;
> >
> > /*
> > - * We have reason to believe the request may be expired. Take a
> > - * reference on the request to lock this request lifetime into its
> > - * currently allocated context to prevent it from being reallocated in
> > - * the event the completion by-passes this timeout handler.
> > - *
> > - * If the reference was already released, then the driver beat the
> > - * timeout handler to posting a natural completion.
> > - */
> > - if (!refcount_inc_not_zero(&rq->ref))
> > - return true;
> > -
> > - /*
> > - * The request is now locked and cannot be reallocated underneath the
> > - * timeout handler's processing. Re-verify this exact request is truly
> > - * expired; if it is not expired, then the request was completed and
> > - * reallocated as a new request.
> > + * Re-verify this exact request is truly expired; if it is not expired,
> > + * then the request was completed and reallocated as a new request
> > + * after returning from blk_mq_check_expired().
> > */
> > if (blk_mq_req_expired(rq, next))
> > blk_mq_rq_timed_out(rq, reserved);
>
> There's no need to check expired twice if the iterator is already taking a
> reference. I had this double check because I didn't want to penalize normal IO
> by preventing it from completing while the timeout handler is running, but it
> looks like the current timeout iterator is going to do that anyway.
Indeed, will clean that in V2.
Thanks,
Ming
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-08-11 15:11 UTC | newest]
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2021-08-11 14:38 [PATCH] blk-mq: don't grab rq's refcount in blk_mq_check_expired() Ming Lei
2021-08-11 14:55 ` Keith Busch
2021-08-11 15:10 ` Ming Lei
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