fs: protect inode->i_state with inode->i_lock

Protect inode state transitions and validity checks with the
inode->i_lock. This enables us to make inode state transitions
independently of the inode_lock and is the first step to peeling
away the inode_lock from the code.

This requires that __iget() is done atomically with i_state checks
during list traversals so that we don't race with another thread
marking the inode I_FREEING between the state check and grabbing the
reference.

Also remove the unlock_new_inode() memory barrier optimisation
required to avoid taking the inode_lock when clearing I_NEW.
Simplify the code by simply taking the inode->i_lock around the
state change and wakeup. Because the wakeup is no longer tricky,
remove the wake_up_inode() function and open code the wakeup where
necessary.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 816f88e6b9ce..6c6f73ba0868 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -18,11 +18,14 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 
         spin_lock(&inode_lock);
         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
-                if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
-                        continue;
-                if (inode->i_mapping->nrpages == 0)
+                spin_lock(&inode->i_lock);
+                if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+                    (inode->i_mapping->nrpages == 0)) {
+                        spin_unlock(&inode->i_lock);
                         continue;
+                }
                 __iget(inode);
+                spin_unlock(&inode->i_lock);
                 spin_unlock(&inode_lock);
                 invalidate_mapping_pages(inode->i_mapping, 0, -1);
                 iput(toput_inode);