[RFC][PATCH 02/10] fs: Avoid looking at i_count without i_lock held

[Peter Zijlstra <peterz@infradead.org>]

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In general i_count will only stay 0 if we have i_lock held. I realize
this is evict, so having MS_ACTIVE cleared might avoid the race
against find_inode_fast() in other ways.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 fs/inode.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/inode.c
+++ b/fs/inode.c
@@ -604,10 +604,12 @@ void evict_inodes(struct super_block *sb
 again:
 	spin_lock(&sb->s_inode_list_lock);
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
-		if (atomic_read(&inode->i_count))
+		spin_lock(&inode->i_lock);
+		if (atomic_read(&inode->i_count)) {
+			spin_unlock(&inode->i_lock);
 			continue;
+		}
 
-		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 			spin_unlock(&inode->i_lock);
 			continue;