Merge branch 'md-next-rcu-cleanup' into md-next

From Yu Kuai:

md: remove rcu protection to access rdev from conf

The lifetime of rdev:

1. md_import_device() generate a rdev based on underlying disk;

   mddev_lock()
   rdev = kzalloc();
   rdev->bdev = blkdev_get_by_dev();
   mddev_unlock()

2. bind_rdev_to_array() add this rdev to mddev->disks;

   mddev_lock()
   kobject_add(&rdev->kobj, &mddev->kobj, ...);
   list_add_rcu(&rdev->same_set, &mddev->disks);
   mddev_unlock()

3. remove_and_add_spares() add this rdev to conf;

   mddev_lock()
   rdev_addable();
   pers->hot_add_disk();
   rcu_assign_pointer(conf->rdev, rdev);
   mddev_unlock()

4. Use this array with rdev;

5. remove_and_add_spares() remove rdev from conf;

   // triggered by sysfs/ioctl
   mddev_lock()
   rdev_removeable();
   pers->hot_remove_disk();
    rcu_assign_pointer(conf->rdev, NULL);
    synchronize_rcu();
   mddev_unlock()

   // triggered by daemon
   mddev_lock()
   rdev_removeable();
   synchronize_rcu(); -> this can't protect accessing rdev from conf
   pers->hot_remove_disk();
    rcu_assign_pointer(conf->rdev, NULL);
   mddev_unlock()

6. md_kick_rdev_from_array() remove rdev from mddev->disks;

   mddev_lock()
   list_del_rcu(&rdev->same_set);
   synchronize_rcu();
   list_add(&rdev->same_set, &mddev->deleting)
   mddev_unlock()
    export_rdev

There are two separate rcu protection for rdev, and this pathset remove
the protection of conf(step 3 and 5), because it's safe to access rdev
from conf in following cases:

 - If 'reconfig_mutex' is held, because rdev can't be added or rmoved to
 conf;
 - If there is normal IO inflight, because mddev_suspend() will wait for
 IO to be done and prevent rdev to be added or removed to conf;
 - If sync thread is running, because remove_and_add_spares() can only be
 called from daemon thread when sync thread is done, and
 'MD_RECOVERY_RUNNING' is also checked for ioctl/sysfs;
 - if any spinlock or rcu_read_lock() is held, because synchronize_rcu()
 from step 6 prevent rdev to be freed until spinlock is released or
 rcu_read_unlock();

Author: liu-song-6

drivers/md/md-multipath.c

@@ -32,17 +32,15 @@ static int multipath_map (struct mpconf *conf)
 	 * now we use the first available disk.
 	 */
 
-	rcu_read_lock();
 	for (i = 0; i < disks; i++) {
-		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
+		struct md_rdev *rdev = conf->multipaths[i].rdev;
+
 		if (rdev && test_bit(In_sync, &rdev->flags) &&
 		    !test_bit(Faulty, &rdev->flags)) {
 			atomic_inc(&rdev->nr_pending);
-			rcu_read_unlock();
 			return i;
 		}
 	}
-	rcu_read_unlock();
 
 	pr_crit_ratelimited("multipath_map(): no more operational IO paths?\n");
 	return (-1);
@@ -137,14 +135,16 @@ static void multipath_status(struct seq_file *seq, struct mddev *mddev)
 	struct mpconf *conf = mddev->private;
 	int i;
 
+	lockdep_assert_held(&mddev->lock);
+
 	seq_printf (seq, " [%d/%d] [", conf->raid_disks,
 		    conf->raid_disks - mddev->degraded);
-	rcu_read_lock();
 	for (i = 0; i < conf->raid_disks; i++) {
-		struct md_rdev *rdev = rcu_dereference(conf->multipaths[i].rdev);
-		seq_printf (seq, "%s", rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
+		struct md_rdev *rdev = READ_ONCE(conf->multipaths[i].rdev);
+
+		seq_printf(seq, "%s",
+			   rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
 	}
-	rcu_read_unlock();
 	seq_putc(seq, ']');
 }
 
@@ -182,7 +182,7 @@ static void multipath_error (struct mddev *mddev, struct md_rdev *rdev)
 	       conf->raid_disks - mddev->degraded);
 }
 
-static void print_multipath_conf (struct mpconf *conf)
+static void print_multipath_conf(struct mpconf *conf)
 {
 	int i;
 	struct multipath_info *tmp;
@@ -195,6 +195,7 @@ static void print_multipath_conf (struct mpconf *conf)
 	pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
 		 conf->raid_disks);
 
+	lockdep_assert_held(&conf->mddev->reconfig_mutex);
 	for (i = 0; i < conf->raid_disks; i++) {
 		tmp = conf->multipaths + i;
 		if (tmp->rdev)
@@ -231,7 +232,7 @@ static int multipath_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 			rdev->raid_disk = path;
 			set_bit(In_sync, &rdev->flags);
 			spin_unlock_irq(&conf->device_lock);
-			rcu_assign_pointer(p->rdev, rdev);
+			WRITE_ONCE(p->rdev, rdev);
 			err = 0;
 			break;
 		}
@@ -257,16 +258,7 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 			err = -EBUSY;
 			goto abort;
 		}
-		p->rdev = NULL;
-		if (!test_bit(RemoveSynchronized, &rdev->flags)) {
-			synchronize_rcu();
-			if (atomic_read(&rdev->nr_pending)) {
-				/* lost the race, try later */
-				err = -EBUSY;
-				p->rdev = rdev;
-				goto abort;
-			}
-		}
+		WRITE_ONCE(p->rdev, NULL);
 		err = md_integrity_register(mddev);
 	}
 abort:

drivers/md/md.c

@@ -9244,44 +9244,19 @@ static int remove_and_add_spares(struct mddev *mddev,
 	struct md_rdev *rdev;
 	int spares = 0;
 	int removed = 0;
-	bool remove_some = false;
 
 	if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
 		/* Mustn't remove devices when resync thread is running */
 		return 0;
 
 	rdev_for_each(rdev, mddev) {
-		if ((this == NULL || rdev == this) &&
-		    rdev->raid_disk >= 0 &&
-		    !test_bit(Blocked, &rdev->flags) &&
-		    test_bit(Faulty, &rdev->flags) &&
-		    atomic_read(&rdev->nr_pending)==0) {
-			/* Faulty non-Blocked devices with nr_pending == 0
-			 * never get nr_pending incremented,
-			 * never get Faulty cleared, and never get Blocked set.
-			 * So we can synchronize_rcu now rather than once per device
-			 */
-			remove_some = true;
-			set_bit(RemoveSynchronized, &rdev->flags);
-		}
-	}
-
-	if (remove_some)
-		synchronize_rcu();
-	rdev_for_each(rdev, mddev) {
-		if ((this == NULL || rdev == this) &&
-		    (test_bit(RemoveSynchronized, &rdev->flags) ||
-		     rdev_removeable(rdev))) {
-			if (mddev->pers->hot_remove_disk(
-				    mddev, rdev) == 0) {
-				sysfs_unlink_rdev(mddev, rdev);
-				rdev->saved_raid_disk = rdev->raid_disk;
-				rdev->raid_disk = -1;
-				removed++;
-			}
+		if ((this == NULL || rdev == this) && rdev_removeable(rdev) &&
+		    !mddev->pers->hot_remove_disk(mddev, rdev)) {
+			sysfs_unlink_rdev(mddev, rdev);
+			rdev->saved_raid_disk = rdev->raid_disk;
+			rdev->raid_disk = -1;
+			removed++;
 		}
-		if (remove_some && test_bit(RemoveSynchronized, &rdev->flags))
-			clear_bit(RemoveSynchronized, &rdev->flags);
 	}
 
 	if (removed && mddev->kobj.sd)

drivers/md/md.h

@@ -190,11 +190,6 @@ enum flag_bits {
 				 * than other devices in the array
 				 */
 	ClusterRemove,
-	RemoveSynchronized,	/* synchronize_rcu() was called after
-				 * this device was known to be faulty,
-				 * so it is safe to remove without
-				 * another synchronize_rcu() call.
-				 */
 	ExternalBbl,            /* External metadata provides bad
 				 * block management for a disk
 				 */

drivers/md/raid1.c

@@ -609,7 +609,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 	int choose_first;
 	int choose_next_idle;
 
-	rcu_read_lock();
 	/*
 	 * Check if we can balance. We can balance on the whole
 	 * device if no resync is going on, or below the resync window.
@@ -642,7 +641,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 		unsigned int pending;
 		bool nonrot;
 
-		rdev = rcu_dereference(conf->mirrors[disk].rdev);
+		rdev = conf->mirrors[disk].rdev;
 		if (r1_bio->bios[disk] == IO_BLOCKED
 		    || rdev == NULL
 		    || test_bit(Faulty, &rdev->flags))
@@ -773,7 +772,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 	}
 
 	if (best_disk >= 0) {
-		rdev = rcu_dereference(conf->mirrors[best_disk].rdev);
+		rdev = conf->mirrors[best_disk].rdev;
 		if (!rdev)
 			goto retry;
 		atomic_inc(&rdev->nr_pending);
@@ -784,7 +783,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
 
 		conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
 	}
-	rcu_read_unlock();
 	*max_sectors = sectors;
 
 	return best_disk;
@@ -1235,14 +1233,12 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 
 	if (r1bio_existed) {
 		/* Need to get the block device name carefully */
-		struct md_rdev *rdev;
-		rcu_read_lock();
-		rdev = rcu_dereference(conf->mirrors[r1_bio->read_disk].rdev);
+		struct md_rdev *rdev = conf->mirrors[r1_bio->read_disk].rdev;
+
 		if (rdev)
 			snprintf(b, sizeof(b), "%pg", rdev->bdev);
 		else
 			strcpy(b, "???");
-		rcu_read_unlock();
 	}
 
 	/*
@@ -1396,10 +1392,9 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 	disks = conf->raid_disks * 2;
 	blocked_rdev = NULL;
-	rcu_read_lock();
 	max_sectors = r1_bio->sectors;
 	for (i = 0;  i < disks; i++) {
-		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		struct md_rdev *rdev = conf->mirrors[i].rdev;
 
 		/*
 		 * The write-behind io is only attempted on drives marked as
@@ -1465,7 +1460,6 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 		}
 		r1_bio->bios[i] = bio;
 	}
-	rcu_read_unlock();
 
 	if (unlikely(blocked_rdev)) {
 		/* Wait for this device to become unblocked */
@@ -1617,15 +1611,16 @@ static void raid1_status(struct seq_file *seq, struct mddev *mddev)
 	struct r1conf *conf = mddev->private;
 	int i;
 
+	lockdep_assert_held(&mddev->lock);
+
 	seq_printf(seq, " [%d/%d] [", conf->raid_disks,
 		   conf->raid_disks - mddev->degraded);
-	rcu_read_lock();
 	for (i = 0; i < conf->raid_disks; i++) {
-		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		struct md_rdev *rdev = READ_ONCE(conf->mirrors[i].rdev);
+
 		seq_printf(seq, "%s",
 			   rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
 	}
-	rcu_read_unlock();
 	seq_printf(seq, "]");
 }
 
@@ -1691,16 +1686,15 @@ static void print_conf(struct r1conf *conf)
 	pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
 		 conf->raid_disks);
 
-	rcu_read_lock();
+	lockdep_assert_held(&conf->mddev->reconfig_mutex);
 	for (i = 0; i < conf->raid_disks; i++) {
-		struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
+		struct md_rdev *rdev = conf->mirrors[i].rdev;
 		if (rdev)
 			pr_debug(" disk %d, wo:%d, o:%d, dev:%pg\n",
 				 i, !test_bit(In_sync, &rdev->flags),
 				 !test_bit(Faulty, &rdev->flags),
 				 rdev->bdev);
 	}
-	rcu_read_unlock();
 }
 
 static void close_sync(struct r1conf *conf)
@@ -1810,7 +1804,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 			 */
 			if (rdev->saved_raid_disk < 0)
 				conf->fullsync = 1;
-			rcu_assign_pointer(p->rdev, rdev);
+			WRITE_ONCE(p->rdev, rdev);
 			break;
 		}
 		if (test_bit(WantReplacement, &p->rdev->flags) &&
@@ -1826,7 +1820,7 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 		rdev->raid_disk = repl_slot;
 		err = 0;
 		conf->fullsync = 1;
-		rcu_assign_pointer(p[conf->raid_disks].rdev, rdev);
+		WRITE_ONCE(p[conf->raid_disks].rdev, rdev);
 	}
 
 	print_conf(conf);
@@ -1862,16 +1856,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 			err = -EBUSY;
 			goto abort;
 		}
-		p->rdev = NULL;
-		if (!test_bit(RemoveSynchronized, &rdev->flags)) {
-			synchronize_rcu();
-			if (atomic_read(&rdev->nr_pending)) {
-				/* lost the race, try later */
-				err = -EBUSY;
-				p->rdev = rdev;
-				goto abort;
-			}
-		}
+		WRITE_ONCE(p->rdev, NULL);
 		if (conf->mirrors[conf->raid_disks + number].rdev) {
 			/* We just removed a device that is being replaced.
 			 * Move down the replacement.  We drain all IO before
@@ -1892,7 +1877,7 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 				goto abort;
 			}
 			clear_bit(Replacement, &repl->flags);
-			p->rdev = repl;
+			WRITE_ONCE(p->rdev, repl);
 			conf->mirrors[conf->raid_disks + number].rdev = NULL;
 			unfreeze_array(conf);
 		}
@@ -2290,24 +2275,22 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
 			sector_t first_bad;
 			int bad_sectors;
 
-			rcu_read_lock();
-			rdev = rcu_dereference(conf->mirrors[d].rdev);
+			rdev = conf->mirrors[d].rdev;
 			if (rdev &&
 			    (test_bit(In_sync, &rdev->flags) ||
 			     (!test_bit(Faulty, &rdev->flags) &&
 			      rdev->recovery_offset >= sect + s)) &&
 			    is_badblock(rdev, sect, s,
 					&first_bad, &bad_sectors) == 0) {
 				atomic_inc(&rdev->nr_pending);
-				rcu_read_unlock();
 				if (sync_page_io(rdev, sect, s<<9,
 					 conf->tmppage, REQ_OP_READ, false))
 					success = 1;
 				rdev_dec_pending(rdev, mddev);
 				if (success)
 					break;
-			} else
-				rcu_read_unlock();
+			}
+
 			d++;
 			if (d == conf->raid_disks * 2)
 				d = 0;
@@ -2326,29 +2309,24 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
 			if (d==0)
 				d = conf->raid_disks * 2;
 			d--;
-			rcu_read_lock();
-			rdev = rcu_dereference(conf->mirrors[d].rdev);
+			rdev = conf->mirrors[d].rdev;
 			if (rdev &&
 			    !test_bit(Faulty, &rdev->flags)) {
 				atomic_inc(&rdev->nr_pending);
-				rcu_read_unlock();
 				r1_sync_page_io(rdev, sect, s,
 						conf->tmppage, WRITE);
 				rdev_dec_pending(rdev, mddev);
-			} else
-				rcu_read_unlock();
+			}
 		}
 		d = start;
 		while (d != read_disk) {
 			if (d==0)
 				d = conf->raid_disks * 2;
 			d--;
-			rcu_read_lock();
-			rdev = rcu_dereference(conf->mirrors[d].rdev);
+			rdev = conf->mirrors[d].rdev;
 			if (rdev &&
 			    !test_bit(Faulty, &rdev->flags)) {
 				atomic_inc(&rdev->nr_pending);
-				rcu_read_unlock();
 				if (r1_sync_page_io(rdev, sect, s,
 						    conf->tmppage, READ)) {
 					atomic_add(s, &rdev->corrected_errors);
@@ -2359,8 +2337,7 @@ static void fix_read_error(struct r1conf *conf, int read_disk,
 						rdev->bdev);
 				}
 				rdev_dec_pending(rdev, mddev);
-			} else
-				rcu_read_unlock();
+			}
 		}
 		sectors -= s;
 		sect += s;
@@ -2741,7 +2718,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 
 	r1_bio = raid1_alloc_init_r1buf(conf);
 
-	rcu_read_lock();
 	/*
 	 * If we get a correctably read error during resync or recovery,
 	 * we might want to read from a different device.  So we
@@ -2762,7 +2738,7 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 		struct md_rdev *rdev;
 		bio = r1_bio->bios[i];
 
-		rdev = rcu_dereference(conf->mirrors[i].rdev);
+		rdev = conf->mirrors[i].rdev;
 		if (rdev == NULL ||
 		    test_bit(Faulty, &rdev->flags)) {
 			if (i < conf->raid_disks)
@@ -2820,7 +2796,6 @@ static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
 				bio->bi_opf |= MD_FAILFAST;
 		}
 	}
-	rcu_read_unlock();
 	if (disk < 0)
 		disk = wonly;
 	r1_bio->read_disk = disk;