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Message-Id: <20231125081604.3939938-6-yukuai1@huaweicloud.com>
Date: Sat, 25 Nov 2023 16:16:04 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: song@...nel.org
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
yukuai3@...wei.com, yukuai1@...weicloud.com, yi.zhang@...wei.com,
yangerkun@...wei.com
Subject: [PATCH -next v3 5/5] md/md-multipath: remove rcu protection to access rdev from conf
From: Yu Kuai <yukuai3@...wei.com>
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@...wei.com>
---
drivers/md/md-multipath.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
diff --git a/drivers/md/md-multipath.c b/drivers/md/md-multipath.c
index aa77133f3188..19c8625ea642 100644
--- 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:
--
2.39.2
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