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Commit 9eca8046 authored by Tejun Heo's avatar Tejun Heo
Browse files

Revert "blk-mq, percpu_ref: implement a kludge for SCSI blk-mq stall during probe" 



This reverts commit 0a30288d, which
was a temporary fix for SCSI blk-mq stall issue.  The following
patches will fix the issue properly by introducing atomic mode to
percpu_ref.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
parent d06efebf

block/blk-mq.c

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



	if (freeze) {

		/*

		 * 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);



		percpu_ref_kill(&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

+0 −1
Original line number Diff line number Diff line
@@ -72,7 +72,6 @@ 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

+0 −16
Original line number Diff line number Diff line
@@ -189,19 +189,3 @@ 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);

}