From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: [md PATCH 15/26] md: remove need for mddev_lock() in md_seq_show() Date: Wed, 04 Feb 2015 08:42:29 +1100 Message-ID: <20150203214229.3448.55762.stgit@notabene.brown> References: <20150203213948.3448.80258.stgit@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150203213948.3448.80258.stgit@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids 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 --- drivers/md/md.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 421d47e2d457..4caa414fe6a3 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -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; }