linux-kernel - [PATCH 5.4 104/165] fs: avoid softlockups in s

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Date:   Sat, 11 Jan 2020 10:50:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Sandeen <sandeen@...hat.com>,
        Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 104/165] fs: avoid softlockups in s_inodes iterators

From: Eric Sandeen <sandeen@...hat.com>

[ Upstream commit 04646aebd30b99f2cfa0182435a2ec252fcb16d0 ]

Anything that walks all inodes on sb->s_inodes list without rescheduling
risks softlockups.

Previous efforts were made in 2 functions, see:

c27d82f fs/drop_caches.c: avoid softlockups in drop_pagecache_sb()
ac05fbb inode: don't softlockup when evicting inodes

but there hasn't been an audit of all walkers, so do that now.  This
also consistently moves the cond_resched() calls to the bottom of each
loop in cases where it already exists.

One loop remains: remove_dquot_ref(), because I'm not quite sure how
to deal with that one w/o taking the i_lock.

Signed-off-by: Eric Sandeen <sandeen@...hat.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/drop_caches.c     | 2 +-
 fs/inode.c           | 7 +++++++
 fs/notify/fsnotify.c | 1 +
 fs/quota/dquot.c     | 1 +
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index d31b6c72b476..dc1a1d5d825b 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -35,11 +35,11 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 		spin_unlock(&inode->i_lock);
 		spin_unlock(&sb->s_inode_list_lock);
 
-		cond_resched();
 		invalidate_mapping_pages(inode->i_mapping, 0, -1);
 		iput(toput_inode);
 		toput_inode = inode;
 
+		cond_resched();
 		spin_lock(&sb->s_inode_list_lock);
 	}
 	spin_unlock(&sb->s_inode_list_lock);
diff --git a/fs/inode.c b/fs/inode.c
index fef457a42882..96d62d97694e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -676,6 +676,7 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
 	struct inode *inode, *next;
 	LIST_HEAD(dispose);
 
+again:
 	spin_lock(&sb->s_inode_list_lock);
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
 		spin_lock(&inode->i_lock);
@@ -698,6 +699,12 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
 		inode_lru_list_del(inode);
 		spin_unlock(&inode->i_lock);
 		list_add(&inode->i_lru, &dispose);
+		if (need_resched()) {
+			spin_unlock(&sb->s_inode_list_lock);
+			cond_resched();
+			dispose_list(&dispose);
+			goto again;
+		}
 	}
 	spin_unlock(&sb->s_inode_list_lock);
 
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 2ecef6155fc0..ac9eb273e28c 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -77,6 +77,7 @@ static void fsnotify_unmount_inodes(struct super_block *sb)
 
 		iput_inode = inode;
 
+		cond_resched();
 		spin_lock(&sb->s_inode_list_lock);
 	}
 	spin_unlock(&sb->s_inode_list_lock);
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 9b96243de081..7abc3230c21a 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -986,6 +986,7 @@ static int add_dquot_ref(struct super_block *sb, int type)
 		 * later.
 		 */
 		old_inode = inode;
+		cond_resched();
 		spin_lock(&sb->s_inode_list_lock);
 	}
 	spin_unlock(&sb->s_inode_list_lock);
-- 
2.20.1