[PATCH v2] block: don't use blocking queue entered for recursive bio submits

[PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Alexandru Moise]

commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.

If we end up splitting a bio and the queue goes away between
the initial submission and the later split submission, then we
can block forever in blk_queue_enter() waiting for the reference
to drop to zero. This will never happen, since we already hold
a reference.

Mark a split bio as already having entered the queue, so we can
just use the live non-blocking queue enter variant.

Thanks to Tetsuo Handa for the analysis.

We're running fio tests and the tasks get stuck in a D state forever
when systemd-udevd tries to read the partition table. This patch solves
it. Please apply to 4.17 stable.

Reported-by: syzbot+c4f9cebf9d651f6e54de@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>
---
v2: Changed "From:" The email sent as being from Jens instead of me,
    sorry again Jens.

 block/blk-core.c          |  4 +++-
 block/blk-merge.c         | 10 ++++++++++
 include/linux/blk_types.h |  2 ++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index b559b9d4f1a2..47ab2d9d02d9 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2392,7 +2392,9 @@ blk_qc_t generic_make_request(struct bio *bio)
 
 	if (bio->bi_opf & REQ_NOWAIT)
 		flags = BLK_MQ_REQ_NOWAIT;
-	if (blk_queue_enter(q, flags) < 0) {
+	if (bio_flagged(bio, BIO_QUEUE_ENTERED))
+		blk_queue_enter_live(q);
+	else if (blk_queue_enter(q, flags) < 0) {
 		if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
 			bio_wouldblock_error(bio);
 		else
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 782940c65d8a..481dc02668f9 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -210,6 +210,16 @@ 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);
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 17b18b91ebac..1602bf4ab4cd 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -186,6 +186,8 @@ struct bio {
 				 * throttling rules. Don't do it again. */
 #define BIO_TRACE_COMPLETION 10	/* bio_endio() should trace the final completion
 				 * of this bio. */
+#define BIO_QUEUE_ENTERED 11	/* can use blk_queue_enter_live() */
+
 /* See BVEC_POOL_OFFSET below before adding new flags */
 
 /*
-- 
2.18.0

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Greg KH]

On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
> commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.

Who wrote this patch?  Please keep the correct ownership of patches...

greg k-h

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Alexandru Moise]

On Wed, Jul 04, 2018 at 11:16:44AM +0200, Greg KH wrote:
> On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
> > commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.
> 
> Who wrote this patch?  Please keep the correct ownership of patches...
> 
This is Jenses work, I have absolutely nothing to do with it. I just want
to make sure it reaches 4.17, I tried my best to follow these guidelines:

https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

I assumed that the first Signed-off is implicitly the author of the patch.
Is there something I am missing? Am I misinterpeting the stable kernel rules?

../Alex

> greg k-h

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Harsh 'Shandilya]

On 4 July 2018 3:25:06 PM IST, Alexandru Moise <00moses.alexander00@gmail.com> wrote:
>On Wed, Jul 04, 2018 at 11:16:44AM +0200, Greg KH wrote:
>> On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
>> > commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.
>> 
>> Who wrote this patch?  Please keep the correct ownership of
>patches...
>> 
>This is Jenses work, I have absolutely nothing to do with it. I just
>want
>to make sure it reaches 4.17, I tried my best to follow these
>guidelines:
>
>https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>
>I assumed that the first Signed-off is implicitly the author of the
>patch.
>Is there something I am missing? Am I misinterpeting the stable kernel
>rules?

If you use git format-patch and git send-email for your patches, they'll come out looking like https://www.spinics.net/lists/stable/msg236090.html, which appears to be the proper format since Greg applied those patches without pointing out any flaws in the format.

Try 
-- 
Harsh Shandilya, PRJKT Development LLC

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Greg KH]

On Wed, Jul 04, 2018 at 04:29:09PM +0530, Harsh 'Shandilya wrote:
> On 4 July 2018 3:25:06 PM IST, Alexandru Moise <00moses.alexander00@gmail.com> wrote:
> >On Wed, Jul 04, 2018 at 11:16:44AM +0200, Greg KH wrote:
> >> On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
> >> > commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.
> >> 
> >> Who wrote this patch?  Please keep the correct ownership of
> >patches...
> >> 
> >This is Jenses work, I have absolutely nothing to do with it. I just
> >want
> >to make sure it reaches 4.17, I tried my best to follow these
> >guidelines:
> >
> >https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> >
> >I assumed that the first Signed-off is implicitly the author of the
> >patch.
> >Is there something I am missing? Am I misinterpeting the stable kernel
> >rules?
> 
> If you use git format-patch and git send-email for your patches,
> they'll come out looking like
> https://www.spinics.net/lists/stable/msg236090.html, which appears to
> be the proper format since Greg applied those patches without pointing
> out any flaws in the format.

That is correct, you need the first line that says "From:" to show that
the patch comes from someone other than you.  Please fix that up and
resend.

thanks,

greg k-h

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Alexandru Moise]

On Wed, Jul 04, 2018 at 01:31:54PM +0200, Greg KH wrote:
> On Wed, Jul 04, 2018 at 04:29:09PM +0530, Harsh 'Shandilya wrote:
> > On 4 July 2018 3:25:06 PM IST, Alexandru Moise <00moses.alexander00@gmail.com> wrote:
> > >On Wed, Jul 04, 2018 at 11:16:44AM +0200, Greg KH wrote:
> > >> On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
> > >> > commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.
> > >> 
> > >> Who wrote this patch?  Please keep the correct ownership of
> > >patches...
> > >> 
> > >This is Jenses work, I have absolutely nothing to do with it. I just
> > >want
> > >to make sure it reaches 4.17, I tried my best to follow these
> > >guidelines:
> > >
> > >https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> > >
> > >I assumed that the first Signed-off is implicitly the author of the
> > >patch.
> > >Is there something I am missing? Am I misinterpeting the stable kernel
> > >rules?
> > 
> > If you use git format-patch and git send-email for your patches,
> > they'll come out looking like
> > https://www.spinics.net/lists/stable/msg236090.html, which appears to
> > be the proper format since Greg applied those patches without pointing
> > out any flaws in the format.
> 
> That is correct, you need the first line that says "From:" to show that
> the patch comes from someone other than you.  Please fix that up and
> resend.
Understood, thank you for your patience. I was used to just sending patches,
with mutt.

../Alex
> 
> thanks,
> 
> greg k-h

Re: [PATCH v2] block: don't use blocking queue entered for recursive bio submits

[Greg KH]

On Wed, Jul 04, 2018 at 01:44:48PM +0200, Alexandru Moise wrote:
> On Wed, Jul 04, 2018 at 01:31:54PM +0200, Greg KH wrote:
> > On Wed, Jul 04, 2018 at 04:29:09PM +0530, Harsh 'Shandilya wrote:
> > > On 4 July 2018 3:25:06 PM IST, Alexandru Moise <00moses.alexander00@gmail.com> wrote:
> > > >On Wed, Jul 04, 2018 at 11:16:44AM +0200, Greg KH wrote:
> > > >> On Tue, Jul 03, 2018 at 11:44:53PM +0200, Alexandru Moise wrote:
> > > >> > commit cd4a4ae4683dc2e09380118e205e057896dcda2b upstream.
> > > >> 
> > > >> Who wrote this patch?  Please keep the correct ownership of
> > > >patches...
> > > >> 
> > > >This is Jenses work, I have absolutely nothing to do with it. I just
> > > >want
> > > >to make sure it reaches 4.17, I tried my best to follow these
> > > >guidelines:
> > > >
> > > >https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> > > >
> > > >I assumed that the first Signed-off is implicitly the author of the
> > > >patch.
> > > >Is there something I am missing? Am I misinterpeting the stable kernel
> > > >rules?
> > > 
> > > If you use git format-patch and git send-email for your patches,
> > > they'll come out looking like
> > > https://www.spinics.net/lists/stable/msg236090.html, which appears to
> > > be the proper format since Greg applied those patches without pointing
> > > out any flaws in the format.
> > 
> > That is correct, you need the first line that says "From:" to show that
> > the patch comes from someone other than you.  Please fix that up and
> > resend.
> Understood, thank you for your patience. I was used to just sending patches,
> with mutt.

mutt works great too, just don't change the author "from:" line :)