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Commit 02f130a7 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'for-linus' of git://git.kernel.dk/linux-block 

Pull one last block fix from Jens Axboe:
 "We've had an issue with scsi-mq where probing takes forever.  This was
  bisected down to the percpu changes for blk_mq_queue_enter(), and the
  fact we now suffer an RCU grace period when killing a queue.  SCSI
  creates and destroys tons of queues, so this let to 10s of seconds of
  stalls at boot for some.

  Tejun has a real fix for this, but it's too involved for 3.17.  So
  this is a temporary workaround to expedite the queue killing until we
  can fold in the real fix for 3.18 when that merge window opens"

* 'for-linus' of git://git.kernel.dk/linux-block:
  blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe
parents 2d7ed01e 0a30288d

block/blk-mq.c

+10 −1
Original line number Diff line number Diff line
@@ -119,7 +119,16 @@ void blk_mq_freeze_queue(struct request_queue *q) 
	spin_unlock_irq(q->queue_lock);



	if (freeze) {

		percpu_ref_kill(&q->mq_usage_counter);

		/*

		 * XXX: Temporary kludge to work around SCSI blk-mq stall.

		 * SCSI synchronously creates and destroys many queues

		 * back-to-back during probe leading to lengthy stalls.

		 * This will be fixed by keeping ->mq_usage_counter in

		 * atomic mode until genhd registration, but, for now,

		 * let's work around using expedited synchronization.

		 */

		__percpu_ref_kill_expedited(&q->mq_usage_counter);



		blk_mq_run_queues(q, false);

	}

	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));

include/linux/percpu-refcount.h

+1 −0
Original line number Diff line number Diff line
@@ -71,6 +71,7 @@ void percpu_ref_reinit(struct percpu_ref *ref); 
void percpu_ref_exit(struct percpu_ref *ref);

void percpu_ref_kill_and_confirm(struct percpu_ref *ref,

				 percpu_ref_func_t *confirm_kill);

void __percpu_ref_kill_expedited(struct percpu_ref *ref);



/**

 * percpu_ref_kill - drop the initial ref

lib/percpu-refcount.c

+16 −0
Original line number Diff line number Diff line
@@ -184,3 +184,19 @@ void percpu_ref_kill_and_confirm(struct percpu_ref *ref, 
	call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);

}

EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);



/*

 * XXX: Temporary kludge to work around SCSI blk-mq stall.  Used only by

 * block/blk-mq.c::blk_mq_freeze_queue().  Will be removed during v3.18

 * devel cycle.  Do not use anywhere else.

 */

void __percpu_ref_kill_expedited(struct percpu_ref *ref)

{

	WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,

		  "percpu_ref_kill() called more than once on %pf!",

		  ref->release);



	ref->pcpu_count_ptr |= PCPU_REF_DEAD;

	synchronize_sched_expedited();

	percpu_ref_kill_rcu(&ref->rcu);

}