From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: [PATCH 7/7] dm-mpath: Fix a race condition in
	__multipath_map()
Date: Wed, 23 Nov 2016 13:50:40 -0500
Message-ID: <20161123185040.GB4609@redhat.com>
References: <81bc399e-df90-099d-1b25-bdb0fda3f27c@sandisk.com>
	<20161116003720.GA19059@redhat.com>
	<be828cfa-1121-8d99-0cd1-9021fab3adc8@sandisk.com>
	<20161121234316.GA25362@redhat.com>
	<d4a3879e-ec60-69f6-abb8-95aa7f305277@sandisk.com>
	<20161122003444.GB25362@redhat.com>
	<a8311b54-cd95-a1f9-7cd2-11adb10eec80@sandisk.com>
	<20161123004803.GA32186@redhat.com>
	<20161123031653.GA17056@redhat.com>
	<3f9f6f82-7240-b47e-e2ca-87a843b79bbc@sandisk.com>
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To: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: device-mapper development <dm-devel@redhat.com>
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On Wed, Nov 23 2016 at  1:28pm -0500,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> On 11/22/2016 07:16 PM, Mike Snitzer wrote:
> >Anyway, this _untested_ patch should hopefully resolve the 'all_blk_mq'
> >inconsistency you saw:
> >
> >diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> >index 8b013ea..8ce81d0 100644
> >--- a/drivers/md/dm-table.c
> >+++ b/drivers/md/dm-table.c
> >@@ -924,12 +924,6 @@ static int dm_table_determine_type(struct dm_table *t)
> >
> > 	BUG_ON(!request_based); /* No targets in this table */
> >
> >-	if (list_empty(devices) && __table_type_request_based(live_md_type)) {
> >-		/* inherit live MD type */
> >-		t->type = live_md_type;
> >-		return 0;
> >-	}
> >-
> > 	/*
> > 	 * The only way to establish DM_TYPE_MQ_REQUEST_BASED is by
> > 	 * having a compatible target use dm_table_set_type.
> >@@ -948,6 +942,19 @@ static int dm_table_determine_type(struct dm_table *t)
> > 		return -EINVAL;
> > 	}
> >
> >+	if (list_empty(devices)) {
> >+		int srcu_idx;
> >+		struct dm_table *live_table = dm_get_live_table(t->md, &srcu_idx);
> >+
> >+		/* inherit live table's type and all_blk_mq */
> >+		if (live_table) {
> >+			t->type = live_table->type;
> >+			t->all_blk_mq = live_table->all_blk_mq;
> >+		}
> >+		dm_put_live_table(t->md, srcu_idx);
> >+		return 0;
> >+	}
> >+
> > 	/* Non-request-stackable devices can't be used for request-based dm */
> > 	list_for_each_entry(dd, devices, list) {
> > 		struct request_queue *q = bdev_get_queue(dd->dm_dev->bdev);
> >
> 
> Hello Mike,
> 
> Thanks for the patch. This patch works fine on my test setup. This
> means that WARN_ON_ONCE(clone && q->mq_ops) is no longer triggered.

Thanks for testing.  I'll get it staged for 4.10 inclusion and marked
for stable.