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md: remove need for mddev_lock() in md_seq_show()

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The only access in md_seq_show that could suffer from races
not protected by ->lock is walking the rdev list.
This can receive sufficient protection from 'rcu'.

So use rdev_for_each_rcu() and get rid of mddev_lock().

Now reading /proc/mdstat will never block in md_seq_show.

Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2014-12-15 12:56:59 +11:00
parent 978a7a47ca
commit f97fcad38f
1 changed files with 3 additions and 5 deletions
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8
drivers/md/md.c
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@ -6950,9 +6950,6 @@ static int md_seq_show(struct seq_file *seq, void *v)
return 0;
}
if (mddev_lock(mddev) < 0)
return -EINTR;
spin_lock(&mddev->lock);
if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {
seq_printf(seq, "%s : %sactive", mdname(mddev),
@ -6966,7 +6963,8 @@ static int md_seq_show(struct seq_file *seq, void *v)
}
sectors = 0;
rdev_for_each(rdev, mddev) {
rcu_read_lock();
rdev_for_each_rcu(rdev, mddev) {
char b[BDEVNAME_SIZE];
seq_printf(seq, " %s[%d]",
bdevname(rdev->bdev,b), rdev->desc_nr);
@ -6982,6 +6980,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
seq_printf(seq, "(R)");
sectors += rdev->sectors;
}
rcu_read_unlock();
if (!list_empty(&mddev->disks)) {
if (mddev->pers)
@ -7025,7 +7024,6 @@ static int md_seq_show(struct seq_file *seq, void *v)
seq_printf(seq, "\n");
}
spin_unlock(&mddev->lock);
mddev_unlock(mddev);
return 0;
}