Remove blkdev warning triggered by using md

As setting and clearing queue flags now requires that we hold a spinlock
on the queue, and as blk_queue_stack_limits is called without that lock,
get the lock inside blk_queue_stack_limits.

For blk_queue_stack_limits to be able to find the right lock, each md
personality needs to set q->queue_lock to point to the appropriate lock.
Those personalities which didn't previously use a spin_lock, us
q->__queue_lock.  So always initialise that lock when allocated.

With this in place, setting/clearing of the QUEUE_FLAG_PLUGGED bit will no
longer cause warnings as it will be clear that the proper lock is held.

Thanks to Dan Williams for review and fixing the silly bugs.

Signed-off-by: NeilBrown <neilb@suse.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Alistair John Strachan <alistair@devzero.co.uk>
Cc: Nick Piggin <npiggin@suse.de>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Jacek Luczak <difrost.kernel@gmail.com>
Cc: Prakash Punnoor <prakash@punnoor.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index bb93d4c32775..8dd86418f35d 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -286,8 +286,14 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
         t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
         t->max_segment_size = min(t->max_segment_size, b->max_segment_size);
         t->hardsect_size = max(t->hardsect_size, b->hardsect_size);
-        if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
+        if (!t->queue_lock)
+                WARN_ON_ONCE(1);
+        else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
+                unsigned long flags;
+                spin_lock_irqsave(t->queue_lock, flags);
                 queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
+                spin_unlock_irqrestore(t->queue_lock, flags);
+        }
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);