md/raid5: replace sh->lock with an 'active' flag.

sh->lock is now mainly used to ensure that two threads aren't running
in the locked part of handle_stripe[56] at the same time.

That can more neatly be achieved with an 'active' flag which we set
while running handle_stripe.  If we find the flag is set, we simply
requeue the stripe for later by setting STRIPE_HANDLE.

For safety we take ->device_lock while examining the state of the
stripe and creating a summary in 'stripe_head_state / r6_state'.
This possibly isn't needed but as shared fields like ->toread,
->towrite are checked it is safer for now at least.

We leave the label after the old 'unlock' called "unlock" because it
will disappear in a few patches, so renaming seems pointless.

This leaves the stripe 'locked' for longer as we clear STRIPE_ACTIVE
later, but that is not a problem.
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Namhyung Kim <namhyung@gmail.com>

drivers/md/raid5.c

@@ -1020,14 +1020,12 @@ ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
 		if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
 			struct bio *wbi;
 
-			spin_lock(&sh->lock);
 			spin_lock_irq(&sh->raid_conf->device_lock);
 			chosen = dev->towrite;
 			dev->towrite = NULL;
 			BUG_ON(dev->written);
 			wbi = dev->written = chosen;
 			spin_unlock_irq(&sh->raid_conf->device_lock);
-			spin_unlock(&sh->lock);
 
 			while (wbi && wbi->bi_sector <
 				dev->sector + STRIPE_SECTORS) {
@@ -1322,7 +1320,6 @@ static int grow_one_stripe(raid5_conf_t *conf)
 		return 0;
 
 	sh->raid_conf = conf;
-	spin_lock_init(&sh->lock);
 	#ifdef CONFIG_MULTICORE_RAID456
 	init_waitqueue_head(&sh->ops.wait_for_ops);
 	#endif
@@ -1442,7 +1439,6 @@ static int resize_stripes(raid5_conf_t *conf, int newsize)
 			break;
 
 		nsh->raid_conf = conf;
-		spin_lock_init(&nsh->lock);
 		#ifdef CONFIG_MULTICORE_RAID456
 		init_waitqueue_head(&nsh->ops.wait_for_ops);
 		#endif
@@ -2148,7 +2144,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
 		(unsigned long long)sh->sector);
 
 
-	spin_lock(&sh->lock);
 	spin_lock_irq(&conf->device_lock);
 	if (forwrite) {
 		bip = &sh->dev[dd_idx].towrite;
@@ -2184,7 +2179,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
 			set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
 	}
 	spin_unlock_irq(&conf->device_lock);
-	spin_unlock(&sh->lock);
 
 	pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
 		(unsigned long long)(*bip)->bi_sector,
@@ -2201,7 +2195,6 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
  overlap:
 	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
 	spin_unlock_irq(&conf->device_lock);
-	spin_unlock(&sh->lock);
 	return 0;
 }
 
@@ -3023,12 +3016,10 @@ static void handle_stripe5(struct stripe_head *sh)
 		 atomic_read(&sh->count), sh->pd_idx, sh->check_state,
 		 sh->reconstruct_state);
 
-	spin_lock(&sh->lock);
 	if (test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
 		set_bit(STRIPE_SYNCING, &sh->state);
 		clear_bit(STRIPE_INSYNC, &sh->state);
 	}
-	clear_bit(STRIPE_HANDLE, &sh->state);
 	clear_bit(STRIPE_DELAYED, &sh->state);
 
 	s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
@@ -3037,6 +3028,7 @@ static void handle_stripe5(struct stripe_head *sh)
 
 	/* Now to look around and see what can be done */
 	rcu_read_lock();
+	spin_lock_irq(&conf->device_lock);
 	for (i=disks; i--; ) {
 		mdk_rdev_t *rdev;
 
@@ -3099,6 +3091,7 @@ static void handle_stripe5(struct stripe_head *sh)
 			s.failed_num = i;
 		}
 	}
+	spin_unlock_irq(&conf->device_lock);
 	rcu_read_unlock();
 
 	if (unlikely(blocked_rdev)) {
@@ -3275,7 +3268,6 @@ static void handle_stripe5(struct stripe_head *sh)
 		handle_stripe_expansion(conf, sh, NULL);
 
  unlock:
-	spin_unlock(&sh->lock);
 
 	/* wait for this device to become unblocked */
 	if (unlikely(blocked_rdev))
@@ -3318,12 +3310,10 @@ static void handle_stripe6(struct stripe_head *sh)
 	       sh->check_state, sh->reconstruct_state);
 	memset(&s, 0, sizeof(s));
 
-	spin_lock(&sh->lock);
 	if (test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
 		set_bit(STRIPE_SYNCING, &sh->state);
 		clear_bit(STRIPE_INSYNC, &sh->state);
 	}
-	clear_bit(STRIPE_HANDLE, &sh->state);
 	clear_bit(STRIPE_DELAYED, &sh->state);
 
 	s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
@@ -3332,6 +3322,7 @@ static void handle_stripe6(struct stripe_head *sh)
 	/* Now to look around and see what can be done */
 
 	rcu_read_lock();
+	spin_lock_irq(&conf->device_lock);
 	for (i=disks; i--; ) {
 		mdk_rdev_t *rdev;
 		dev = &sh->dev[i];
@@ -3395,6 +3386,7 @@ static void handle_stripe6(struct stripe_head *sh)
 			s.failed++;
 		}
 	}
+	spin_unlock_irq(&conf->device_lock);
 	rcu_read_unlock();
 
 	if (unlikely(blocked_rdev)) {
@@ -3580,7 +3572,6 @@ static void handle_stripe6(struct stripe_head *sh)
 		handle_stripe_expansion(conf, sh, &r6s);
 
  unlock:
-	spin_unlock(&sh->lock);
 
 	/* wait for this device to become unblocked */
 	if (unlikely(blocked_rdev))
@@ -3608,10 +3599,19 @@ static void handle_stripe6(struct stripe_head *sh)
 
 static void handle_stripe(struct stripe_head *sh)
 {
+	clear_bit(STRIPE_HANDLE, &sh->state);
+	if (test_and_set_bit(STRIPE_ACTIVE, &sh->state)) {
+		/* already being handled, ensure it gets handled
+		 * again when current action finishes */
+		set_bit(STRIPE_HANDLE, &sh->state);
+		return;
+	}
+
 	if (sh->raid_conf->level == 6)
 		handle_stripe6(sh);
 	else
 		handle_stripe5(sh);
+	clear_bit(STRIPE_ACTIVE, &sh->state);
 }
 
 static void raid5_activate_delayed(raid5_conf_t *conf)

drivers/md/raid5.h

@@ -6,11 +6,11 @@
 
 /*
  *
- * Each stripe contains one buffer per disc.  Each buffer can be in
+ * Each stripe contains one buffer per device.  Each buffer can be in
  * one of a number of states stored in "flags".  Changes between
- * these states happen *almost* exclusively under a per-stripe
- * spinlock.  Some very specific changes can happen in bi_end_io, and
- * these are not protected by the spin lock.
+ * these states happen *almost* exclusively under the protection of the
+ * STRIPE_ACTIVE flag.  Some very specific changes can happen in bi_end_io, and
+ * these are not protected by STRIPE_ACTIVE.
  *
  * The flag bits that are used to represent these states are:
  *   R5_UPTODATE and R5_LOCKED
@@ -76,12 +76,10 @@
  * block and the cached buffer are successfully written, any buffer on
  * a written list can be returned with b_end_io.
  *
- * The write list and read list both act as fifos.  The read list is
- * protected by the device_lock.  The write and written lists are
- * protected by the stripe lock.  The device_lock, which can be
- * claimed while the stipe lock is held, is only for list
- * manipulations and will only be held for a very short time.  It can
- * be claimed from interrupts.
+ * The write list and read list both act as fifos.  The read list,
+ * write list and written list are protected by the device_lock.
+ * The device_lock is only for list manipulations and will only be
+ * held for a very short time.  It can be claimed from interrupts.
  *
  *
  * Stripes in the stripe cache can be on one of two lists (or on
@@ -96,7 +94,6 @@
  *
  * The inactive_list, handle_list and hash bucket lists are all protected by the
  * device_lock.
- *  - stripes on the inactive_list never have their stripe_lock held.
  *  - stripes have a reference counter. If count==0, they are on a list.
  *  - If a stripe might need handling, STRIPE_HANDLE is set.
  *  - When refcount reaches zero, then if STRIPE_HANDLE it is put on
@@ -116,10 +113,10 @@
  *  attach a request to an active stripe (add_stripe_bh())
  *     lockdev attach-buffer unlockdev
  *  handle a stripe (handle_stripe())
- *     lockstripe clrSTRIPE_HANDLE ...
+ *     setSTRIPE_ACTIVE,  clrSTRIPE_HANDLE ...
  *		(lockdev check-buffers unlockdev) ..
  *		change-state ..
- *		record io/ops needed unlockstripe schedule io/ops
+ *		record io/ops needed clearSTRIPE_ACTIVE schedule io/ops
  *  release an active stripe (release_stripe())
  *     lockdev if (!--cnt) { if  STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
  *
@@ -128,8 +125,7 @@
  * on a cached buffer, and plus one if the stripe is undergoing stripe
  * operations.
  *
- * Stripe operations are performed outside the stripe lock,
- * the stripe operations are:
+ * The stripe operations are:
  * -copying data between the stripe cache and user application buffers
  * -computing blocks to save a disk access, or to recover a missing block
  * -updating the parity on a write operation (reconstruct write and
@@ -159,7 +155,8 @@
  */
 
 /*
- * Operations state - intermediate states that are visible outside of sh->lock
+ * Operations state - intermediate states that are visible outside of 
+ *   STRIPE_ACTIVE.
  * In general _idle indicates nothing is running, _run indicates a data
  * processing operation is active, and _result means the data processing result
  * is stable and can be acted upon.  For simple operations like biofill and
@@ -209,7 +206,6 @@ struct stripe_head {
 	short			ddf_layout;/* use DDF ordering to calculate Q */
 	unsigned long		state;		/* state flags */
 	atomic_t		count;	      /* nr of active thread/requests */
-	spinlock_t		lock;
 	int			bm_seq;	/* sequence number for bitmap flushes */
 	int			disks;		/* disks in stripe */
 	enum check_states	check_state;
@@ -240,7 +236,7 @@ struct stripe_head {
 };
 
 /* stripe_head_state - collects and tracks the dynamic state of a stripe_head
- *     for handle_stripe.  It is only valid under spin_lock(sh->lock);
+ *     for handle_stripe.
  */
 struct stripe_head_state {
 	int syncing, expanding, expanded;
@@ -290,6 +286,7 @@ struct r6_state {
  * Stripe state
  */
 enum {
+	STRIPE_ACTIVE,
 	STRIPE_HANDLE,
 	STRIPE_SYNC_REQUESTED,
 	STRIPE_SYNCING,
@@ -339,7 +336,7 @@ enum {
  * PREREAD_ACTIVE.
  * In stripe_handle, if we find pre-reading is necessary, we do it if
  * PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
- * HANDLE gets cleared if stripe_handle leave nothing locked.
+ * HANDLE gets cleared if stripe_handle leaves nothing locked.
  */