md/md-multipath: remove rcu protection to access rdev from conf

Because it's safe to accees rdev from conf:
 - If any spinlock is held, because synchronize_rcu() from
   md_kick_rdev_from_array() will prevent 'rdev' to be freed until
   spinlock is released;
 - If there is normal IO inflight, because mddev_suspend() will prevent
   rdev to be added or removed from array;

And these will cover all the scenarios in md-multipath.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231125081604.3939938-6-yukuai1@huaweicloud.com

diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index aa77133..19c8625 100644 (file)
--- a/drivers/md/md-multipath.c
+++ b/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;
                }
@@ -257,7 +258,7 @@ static int multipath_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
                        err = -EBUSY;
                        goto abort;
                }
-               p->rdev = NULL;
+               WRITE_ONCE(p->rdev, NULL);
                err = md_integrity_register(mddev);
        }
 abort: