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, 34 insertions, 10 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 59c6e4956786..efd1ebe879cc 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -306,10 +306,12 @@ static void inode_wait_for_writeback(struct inode *inode)
         wait_queue_head_t *wqh;
 
         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
-         while (inode->i_state & I_SYNC) {
+        while (inode->i_state & I_SYNC) {
+                spin_unlock(&inode->i_lock);
                 spin_unlock(&inode_lock);
                 __wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
                 spin_lock(&inode_lock);
+                spin_lock(&inode->i_lock);
         }
 }
 
@@ -333,6 +335,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         unsigned dirty;
         int ret;
 
+        spin_lock(&inode->i_lock);
         if (!atomic_read(&inode->i_count))
                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
         else
@@ -348,6 +351,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                  * completed a full scan of b_io.
                  */
                 if (wbc->sync_mode != WB_SYNC_ALL) {
+                        spin_unlock(&inode->i_lock);
                         requeue_io(inode);
                         return 0;
                 }
@@ -363,6 +367,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         /* Set I_SYNC, reset I_DIRTY_PAGES */
         inode->i_state |= I_SYNC;
         inode->i_state &= ~I_DIRTY_PAGES;
+        spin_unlock(&inode->i_lock);
         spin_unlock(&inode_lock);
 
         ret = do_writepages(mapping, wbc);
@@ -384,8 +389,10 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
          * write_inode()
          */
         spin_lock(&inode_lock);
+        spin_lock(&inode->i_lock);
         dirty = inode->i_state & I_DIRTY;
         inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
+        spin_unlock(&inode->i_lock);
         spin_unlock(&inode_lock);
         /* Don't write the inode if only I_DIRTY_PAGES was set */
         if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
@@ -395,6 +402,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         }
 
         spin_lock(&inode_lock);
+        spin_lock(&inode->i_lock);
         inode->i_state &= ~I_SYNC;
         if (!(inode->i_state & I_FREEING)) {
                 if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
@@ -436,6 +444,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                 }
         }
         inode_sync_complete(inode);
+        spin_unlock(&inode->i_lock);
         return ret;
 }
 
@@ -506,7 +515,9 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                  * kind does not need peridic writeout yet, and for the latter
                  * kind writeout is handled by the freer.
                  */
+                spin_lock(&inode->i_lock);
                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+                        spin_unlock(&inode->i_lock);
                         requeue_io(inode);
                         continue;
                 }
@@ -515,10 +526,14 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                  * Was this inode dirtied after sync_sb_inodes was called?
                  * This keeps sync from extra jobs and livelock.
                  */
-                if (inode_dirtied_after(inode, wbc->wb_start))
+                if (inode_dirtied_after(inode, wbc->wb_start)) {
+                        spin_unlock(&inode->i_lock);
                         return 1;
+                }
 
                 __iget(inode);
+                spin_unlock(&inode->i_lock);
+
                 pages_skipped = wbc->pages_skipped;
                 writeback_single_inode(inode, wbc);
                 if (wbc->pages_skipped != pages_skipped) {
@@ -724,7 +739,9 @@ static long wb_writeback(struct bdi_writeback *wb,
                 if (!list_empty(&wb->b_more_io))  {
                         inode = wb_inode(wb->b_more_io.prev);
                         trace_wbc_writeback_wait(&wbc, wb->bdi);
+                        spin_lock(&inode->i_lock);
                         inode_wait_for_writeback(inode);
+                        spin_unlock(&inode->i_lock);
                 }
                 spin_unlock(&inode_lock);
         }
@@ -1017,6 +1034,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                 block_dump___mark_inode_dirty(inode);
 
         spin_lock(&inode_lock);
+        spin_lock(&inode->i_lock);
         if ((inode->i_state & flags) != flags) {
                 const int was_dirty = inode->i_state & I_DIRTY;
 
@@ -1028,7 +1046,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                  * superblock list, based upon its state.
                  */
                 if (inode->i_state & I_SYNC)
-                        goto out;
+                        goto out_unlock_inode;
 
                 /*
                  * Only add valid (hashed) inodes to the superblock's
@@ -1036,11 +1054,12 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                  */
                 if (!S_ISBLK(inode->i_mode)) {
                         if (inode_unhashed(inode))
-                                goto out;
+                                goto out_unlock_inode;
                 }
                 if (inode->i_state & I_FREEING)
-                        goto out;
+                        goto out_unlock_inode;
 
+                spin_unlock(&inode->i_lock);
                 /*
                  * If the inode was already on b_dirty/b_io/b_more_io, don't
                  * reposition it (that would break b_dirty time-ordering).
@@ -1065,7 +1084,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                         inode->dirtied_when = jiffies;
                         list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
                 }
+                goto out;
         }
+out_unlock_inode:
+        spin_unlock(&inode->i_lock);
 out:
         spin_unlock(&inode_lock);
 
@@ -1111,14 +1133,16 @@ static void wait_sb_inodes(struct super_block *sb)
          * we still have to wait for that writeout.
          */
         list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
-                struct address_space *mapping;
+                struct address_space *mapping = inode->i_mapping;
 
-                if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW))
-                        continue;
-                mapping = inode->i_mapping;
-                if (mapping->nrpages == 0)
+                spin_lock(&inode->i_lock);
+                if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
+                    (mapping->nrpages == 0)) {
+                        spin_unlock(&inode->i_lock);
                         continue;
+                }
                 __iget(inode);
+                spin_unlock(&inode->i_lock);
                 spin_unlock(&inode_lock);
                 /*
                  * We hold a reference to 'inode' so it couldn't have