Eric Lee / smarc-ti-linux-kernel

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Commit 02f130a7872d26bd6ceb4e86b531761d79ac76b7

Authored by Linus Torvalds
2 parents 2d7ed01e5b 0a30288da1
Exists in ti-lsk-linux-4.1.y and in 10 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04

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

Showing 3 changed files Side-by-side Diff

... ... @@ -119,7 +119,16 @@
119 119 spin_unlock_irq(q->queue_lock);
120 120  
121 121 if (freeze) {
122   - percpu_ref_kill(&q->mq_usage_counter);
  122 + /*
  123 + * XXX: Temporary kludge to work around SCSI blk-mq stall.
  124 + * SCSI synchronously creates and destroys many queues
  125 + * back-to-back during probe leading to lengthy stalls.
  126 + * This will be fixed by keeping ->mq_usage_counter in
  127 + * atomic mode until genhd registration, but, for now,
  128 + * let's work around using expedited synchronization.
  129 + */
  130 + __percpu_ref_kill_expedited(&q->mq_usage_counter);
  131 +
123 132 blk_mq_run_queues(q, false);
124 133 }
125 134 wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
include/linux/percpu-refcount.h
Diff comments   View file @ 02f130a
... ... @@ -71,6 +71,7 @@
71 71 void percpu_ref_exit(struct percpu_ref *ref);
72 72 void percpu_ref_kill_and_confirm(struct percpu_ref *ref,
73 73 percpu_ref_func_t *confirm_kill);
  74 +void __percpu_ref_kill_expedited(struct percpu_ref *ref);
74 75  
75 76 /**
76 77 * percpu_ref_kill - drop the initial ref
lib/percpu-refcount.c
Diff comments   View file @ 02f130a
... ... @@ -184,4 +184,20 @@
184 184 call_rcu_sched(&ref->rcu, percpu_ref_kill_rcu);
185 185 }
186 186 EXPORT_SYMBOL_GPL(percpu_ref_kill_and_confirm);
  187 +
  188 +/*
  189 + * XXX: Temporary kludge to work around SCSI blk-mq stall. Used only by
  190 + * block/blk-mq.c::blk_mq_freeze_queue(). Will be removed during v3.18
  191 + * devel cycle. Do not use anywhere else.
  192 + */
  193 +void __percpu_ref_kill_expedited(struct percpu_ref *ref)
  194 +{
  195 + WARN_ONCE(ref->pcpu_count_ptr & PCPU_REF_DEAD,
  196 + "percpu_ref_kill() called more than once on %pf!",
  197 + ref->release);
  198 +
  199 + ref->pcpu_count_ptr |= PCPU_REF_DEAD;
  200 + synchronize_sched_expedited();
  201 + percpu_ref_kill_rcu(&ref->rcu);
  202 +}