[Devel] [PATCH rh7] block/ploop: Add resched points in ploop thread.

[Andrey Ryabinin]

Ploop thread may not reschedule for a long time and cause softlockup
warnings on a debug kernel:

 NMI watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [ploop56082:13917]
...
 RIP: 0010:[<ffffffff8256f426>]  [<ffffffff8256f426>] _raw_spin_unlock_irqrestore+0x46/0xc0
...
 Call Trace:
  [<ffffffff816194f7>] __slab_free+0x207/0x2f0
  [<ffffffff81619ff1>] kmem_cache_free+0x2d1/0x380
  [<ffffffff81514412>] mempool_free_slab+0x22/0x30
  [<ffffffff815159ae>] mempool_free+0x14e/0x1f0
  [<ffffffff81747d6a>] bio_put+0x17a/0x270
  [<ffffffff81735837>] end_bio_bh_io_sync+0xc7/0x120
  [<ffffffff81747d6a>] bio_put+0x17a/0x270
  [<ffffffff81735837>] end_bio_bh_io_sync+0xc7/0x120
  [<ffffffff8174a5ac>] bio_endio+0x13c/0x220
  [<ffffffffa0858a38>] ploop_complete_request+0x148/0x1c60 [ploop]
  [<ffffffffa086b06d>] ploop_req_state_process+0x1f7d/0x3870 [ploop]
  [<ffffffffa086cfce>] ploop_thread+0x66e/0x1170 [ploop]
  [<ffffffff8121dcb6>] kthread+0x1e6/0x250
  [<ffffffff8258ae58>] ret_from_fork+0x58/0x90

Add cond_resched() on each iteration of the ploop_thread() to fix that.

https://jira.sw.ru/browse/PSBM-66617
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 drivers/block/ploop/dev.c     | 22 ++++++++++------------
 drivers/block/ploop/discard.c |  2 +-
 include/linux/ploop/ploop.h   |  3 +--
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
index e7aec54172c0..eab6cb067708 100644
--- a/drivers/block/ploop/dev.c
+++ b/drivers/block/ploop/dev.c
@@ -230,8 +230,7 @@ static void ploop_test_and_clear_blockable(struct ploop_device *plo,
 }
 
 /* always called with plo->lock released */
-void ploop_preq_drop(struct ploop_device * plo, struct list_head *drop_list,
-		      int keep_locked)
+void ploop_preq_drop(struct ploop_device * plo, struct list_head *drop_list)
 {
 	struct ploop_request * preq;
 	int drop_qlen = 0;
@@ -261,8 +260,7 @@ void ploop_preq_drop(struct ploop_device * plo, struct list_head *drop_list,
 
 	ploop_uncongest(plo);
 
-	if (!keep_locked)
-		spin_unlock_irq(&plo->lock);
+	spin_unlock_irq(&plo->lock);
 }
 
 static void merge_rw_flags_to_req(unsigned long rw,
@@ -1066,7 +1064,7 @@ out:
 	blk_check_plugged(ploop_unplug, plo, sizeof(struct blk_plug_cb));
 
 	if (!list_empty(&drop_list))
-		ploop_preq_drop(plo, &drop_list, 0);
+		ploop_preq_drop(plo, &drop_list);
 
 	return;
 }
@@ -2964,12 +2962,12 @@ static int ploop_thread(void * data)
 	set_user_nice(current, -20);
 
 	blk_start_plug(&plug);
-	spin_lock_irq(&plo->lock);
 	for (;;) {
 		/* Convert bios to preqs early (at least before processing
 		 * entry queue) to increase chances of bio merge
 		 */
-	again:
+		cond_resched();
+		spin_lock_irq(&plo->lock);
 		BUG_ON (!list_empty(&drop_list));
 
 		process_pending_bios(plo, &drop_list);
@@ -2978,8 +2976,8 @@ static int ploop_thread(void * data)
 
 		if (!list_empty(&drop_list)) {
 			spin_unlock_irq(&plo->lock);
-			ploop_preq_drop(plo, &drop_list, 1);
-			goto again;
+			ploop_preq_drop(plo, &drop_list);
+			continue;
 		}
 
 		if (!list_empty(&plo->ready_queue)) {
@@ -2991,7 +2989,6 @@ static int ploop_thread(void * data)
 
 			ploop_req_state_process(preq);
 
-			spin_lock_irq(&plo->lock);
 			continue;
 		}
 
@@ -3010,6 +3007,7 @@ static int ploop_thread(void * data)
 				set_bit(PLOOP_S_ATTENTION, &plo->state);
 				if (plo->active_reqs) {
 					list_add(&preq->list, &plo->entry_queue);
+					spin_unlock_irq(&plo->lock);
 					continue;
 				}
 				plo->barrier_reqs--;
@@ -3042,8 +3040,6 @@ static int ploop_thread(void * data)
 			spin_unlock_irq(&plo->lock);
 
 			ploop_req_state_process(preq);
-
-			spin_lock_irq(&plo->lock);
 			continue;
 		}
 
@@ -3058,8 +3054,10 @@ static int ploop_thread(void * data)
 
 wait_more:
 		ploop_wait(plo, once, &plug);
+		spin_unlock_irq(&plo->lock);
 		once = 0;
 	}
+
 	spin_unlock_irq(&plo->lock);
 	blk_finish_plug(&plug);
 
diff --git a/drivers/block/ploop/discard.c b/drivers/block/ploop/discard.c
index 828ab3696469..33122497b9c5 100644
--- a/drivers/block/ploop/discard.c
+++ b/drivers/block/ploop/discard.c
@@ -66,7 +66,7 @@ int ploop_discard_fini_ioc(struct ploop_device *plo)
 	spin_unlock_irq(&plo->lock);
 
 	if (!list_empty(&drop_list))
-		ploop_preq_drop(plo, &drop_list, 0);
+		ploop_preq_drop(plo, &drop_list);
 
 	if (plo->maintenance_type != PLOOP_MNTN_DISCARD) {
 		ret = -EBUSY;
diff --git a/include/linux/ploop/ploop.h b/include/linux/ploop/ploop.h
index c7261c4bda57..f13b7caa4128 100644
--- a/include/linux/ploop/ploop.h
+++ b/include/linux/ploop/ploop.h
@@ -633,8 +633,7 @@ static inline struct ploop_delta * map_top_delta(struct ploop_map * map)
 
 void ploop_complete_io_state(struct ploop_request * preq);
 void ploop_fail_request(struct ploop_request * preq, int err);
-void ploop_preq_drop(struct ploop_device * plo, struct list_head *drop_list,
-		      int keep_locked);
+void ploop_preq_drop(struct ploop_device * plo, struct list_head *drop_list);
 
 
 static inline int ploop_req_delay_fua_possible(struct ploop_request *preq)
-- 
2.13.0