[PATCH V2] fs: avoid softlockups in s_inodes iterators

[Eric Sandeen <sandeen@redhat.com>]

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@redhat.com>
---

V2: Drop unrelated iput cleanups in fsnotify

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..b0c789bb3dba 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 +699,13 @@ 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 6e826b454082..4a085b3c7cac 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -985,6 +985,7 @@ 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);