* [PATCH] block: cover another queue enter recursion via BIO_QUEUE_ENTERED
@ 2019-01-22 8:20 Ming Lei
2019-01-22 17:15 ` Mike Snitzer
0 siblings, 1 reply; 3+ messages in thread
From: Ming Lei @ 2019-01-22 8:20 UTC (permalink / raw)
To: Jens Axboe; +Cc: linux-block, Ming Lei, Tetsuo Handa, Mike Snitzer, NeilBrown
Except for blk_queue_split(), bio_split() is used for splitting bio too,
then the remained bio is often resubmit to queue via generic_make_request().
So the same queue enter recursion exits in this case too. Unfortunatley
commit cd4a4ae4683dc2 doesn't help this case.
This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
q->make_request_fn.
In theory the per-bio flag is used to simulate one stack variable, it is
just fine to clear it after q->make_request_fn is returned. Especially
the same bio can't be submitted from another context.
Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: NeilBrown <neilb@suse.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-core.c | 11 +++++++++++
block/blk-merge.c | 10 ----------
2 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 3c5f61ceeb67..1ccec27d20c3 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1083,7 +1083,18 @@ blk_qc_t generic_make_request(struct bio *bio)
/* Create a fresh bio_list for all subordinate requests */
bio_list_on_stack[1] = bio_list_on_stack[0];
bio_list_init(&bio_list_on_stack[0]);
+
+ /*
+ * Since we're recursing into make_request here, ensure
+ * that we mark this bio as already having entered the queue.
+ * If not, and the queue is going away, we can get stuck
+ * forever on waiting for the queue reference to drop. But
+ * that will never happen, as we're already holding a
+ * reference to it.
+ */
+ bio_set_flag(bio, BIO_QUEUE_ENTERED);
ret = q->make_request_fn(q, bio);
+ bio_clear_flag(bio, BIO_QUEUE_ENTERED);
/* sort new bios into those for a lower level
* and those for the same level
diff --git a/block/blk-merge.c b/block/blk-merge.c
index b990853f6de7..8777e286bd3f 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -339,16 +339,6 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
/* there isn't chance to merge the splitted bio */
split->bi_opf |= REQ_NOMERGE;
- /*
- * Since we're recursing into make_request here, ensure
- * that we mark this bio as already having entered the queue.
- * If not, and the queue is going away, we can get stuck
- * forever on waiting for the queue reference to drop. But
- * that will never happen, as we're already holding a
- * reference to it.
- */
- bio_set_flag(*bio, BIO_QUEUE_ENTERED);
-
bio_chain(split, *bio);
trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
generic_make_request(*bio);
--
2.9.5
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: block: cover another queue enter recursion via BIO_QUEUE_ENTERED
2019-01-22 8:20 [PATCH] block: cover another queue enter recursion via BIO_QUEUE_ENTERED Ming Lei
@ 2019-01-22 17:15 ` Mike Snitzer
2019-01-22 17:16 ` Jens Axboe
0 siblings, 1 reply; 3+ messages in thread
From: Mike Snitzer @ 2019-01-22 17:15 UTC (permalink / raw)
To: Ming Lei, Jens Axboe; +Cc: linux-block, Tetsuo Handa, NeilBrown
On Tue, Jan 22 2019 at 3:20am -0500,
Ming Lei <ming.lei@redhat.com> wrote:
> Except for blk_queue_split(), bio_split() is used for splitting bio too,
> then the remained bio is often resubmit to queue via generic_make_request().
> So the same queue enter recursion exits in this case too. Unfortunatley
> commit cd4a4ae4683dc2 doesn't help this case.
>
> This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
> q->make_request_fn.
>
> In theory the per-bio flag is used to simulate one stack variable, it is
> just fine to clear it after q->make_request_fn is returned. Especially
> the same bio can't be submitted from another context.
>
> Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: NeilBrown <neilb@suse.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
Looks good, I'll drop my DM patch that set/cleared BIO_QUEUE_ENTERED.
Jens, you OK with picking this up for 5.0-rc?
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: block: cover another queue enter recursion via BIO_QUEUE_ENTERED
2019-01-22 17:15 ` Mike Snitzer
@ 2019-01-22 17:16 ` Jens Axboe
0 siblings, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2019-01-22 17:16 UTC (permalink / raw)
To: Mike Snitzer, Ming Lei; +Cc: linux-block, Tetsuo Handa, NeilBrown
On 1/22/19 10:15 AM, Mike Snitzer wrote:
> On Tue, Jan 22 2019 at 3:20am -0500,
> Ming Lei <ming.lei@redhat.com> wrote:
>
>> Except for blk_queue_split(), bio_split() is used for splitting bio too,
>> then the remained bio is often resubmit to queue via generic_make_request().
>> So the same queue enter recursion exits in this case too. Unfortunatley
>> commit cd4a4ae4683dc2 doesn't help this case.
>>
>> This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
>> q->make_request_fn.
>>
>> In theory the per-bio flag is used to simulate one stack variable, it is
>> just fine to clear it after q->make_request_fn is returned. Especially
>> the same bio can't be submitted from another context.
>>
>> Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
>> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Cc: Mike Snitzer <snitzer@redhat.com>
>> Cc: NeilBrown <neilb@suse.com>
>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>
> Looks good, I'll drop my DM patch that set/cleared BIO_QUEUE_ENTERED.
>
> Jens, you OK with picking this up for 5.0-rc?
>
> Reviewed-by: Mike Snitzer <snitzer@redhat.com>
I am, thanks both of you for looking into this. I'm a bit behind on email
and patches from over the long weekend.
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-01-22 17:15 ` Mike Snitzer
2019-01-22 17:16 ` Jens Axboe
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