[PATCH 1/3] Replace I_LOCK with I_SYNC for fs/fs-writeback.c uses.

["Jörn Engel" <joern@lazybastard.org>]

The users of I_LOCK in fs/fs-writeback appear to be independent of
all others.  On top, sharing the same bit for __sync_single_inode()
and ifind/ifind_fast caused deadlocks in both LogFS and NTFS.

Introduce a new bit and use that for fs/fs-writeback.c users.
---
 fs/fs-writeback.c         |   39 ++++++++++++++++++++++++---------------
 include/linux/fs.h        |    2 ++
 include/linux/writeback.h |    7 +++++++
 3 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index a4b142a..4958fae 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -99,11 +99,11 @@ void __mark_inode_dirty(struct inode *in
 		inode->i_state |= flags;
 
 		/*
-		 * If the inode is locked, just update its dirty state. 
+		 * If the inode is being synced, just update its dirty state.
 		 * The unlocker will place the inode on the appropriate
 		 * superblock list, based upon its state.
 		 */
-		if (inode->i_state & I_LOCK)
+		if (inode->i_state & I_SYNC)
 			goto out;
 
 		/*
@@ -139,6 +139,15 @@ static int write_inode(struct inode *ino
 	return 0;
 }
 
+static void inode_sync_complete(struct inode *inode)
+{
+	/*
+	 * Prevent speculative execution through spin_unlock(&inode_lock);
+	 */
+	smp_mb();
+	wake_up_bit(&inode->i_state, __I_SYNC);
+}
+
 /*
  * Write a single inode's dirty pages and inode data out to disk.
  * If `wait' is set, wait on the writeout.
@@ -158,11 +167,11 @@ __sync_single_inode(struct inode *inode,
 	int wait = wbc->sync_mode == WB_SYNC_ALL;
 	int ret;
 
-	BUG_ON(inode->i_state & I_LOCK);
+	BUG_ON(inode->i_state & I_SYNC);
 
-	/* Set I_LOCK, reset I_DIRTY */
+	/* Set I_SYNC, reset I_DIRTY */
 	dirty = inode->i_state & I_DIRTY;
-	inode->i_state |= I_LOCK;
+	inode->i_state |= I_SYNC;
 	inode->i_state &= ~I_DIRTY;
 
 	spin_unlock(&inode_lock);
@@ -183,7 +192,7 @@ __sync_single_inode(struct inode *inode,
 	}
 
 	spin_lock(&inode_lock);
-	inode->i_state &= ~I_LOCK;
+	inode->i_state &= ~I_SYNC;
 	if (!(inode->i_state & I_FREEING)) {
 		if (!(inode->i_state & I_DIRTY) &&
 		    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
@@ -231,7 +240,7 @@ __sync_single_inode(struct inode *inode,
 			list_move(&inode->i_list, &inode_unused);
 		}
 	}
-	wake_up_inode(inode);
+	inode_sync_complete(inode);
 	return ret;
 }
 
@@ -250,7 +259,7 @@ __writeback_single_inode(struct inode *i
 	else
 		WARN_ON(inode->i_state & I_WILL_FREE);
 
-	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_LOCK)) {
+	if ((wbc->sync_mode != WB_SYNC_ALL) && (inode->i_state & I_SYNC)) {
 		struct address_space *mapping = inode->i_mapping;
 		int ret;
 
@@ -269,16 +278,16 @@ __writeback_single_inode(struct inode *i
 	/*
 	 * It's a data-integrity sync.  We must wait.
 	 */
-	if (inode->i_state & I_LOCK) {
-		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_LOCK);
+	if (inode->i_state & I_SYNC) {
+		DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 
-		wqh = bit_waitqueue(&inode->i_state, __I_LOCK);
+		wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 		do {
 			spin_unlock(&inode_lock);
 			__wait_on_bit(wqh, &wq, inode_wait,
 							TASK_UNINTERRUPTIBLE);
 			spin_lock(&inode_lock);
-		} while (inode->i_state & I_LOCK);
+		} while (inode->i_state & I_SYNC);
 	}
 	return __sync_single_inode(inode, wbc);
 }
@@ -311,7 +320,7 @@ __writeback_single_inode(struct inode *i
  * The inodes to be written are parked on sb->s_io.  They are moved back onto
  * sb->s_dirty as they are selected for writing.  This way, none can be missed
  * on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on __wait_on_inode.
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
  */
 static void
 sync_sb_inodes(struct super_block *sb, struct writeback_control *wbc)
@@ -583,7 +592,7 @@ int write_inode_now(struct inode *inode,
 	ret = __writeback_single_inode(inode, &wbc);
 	spin_unlock(&inode_lock);
 	if (sync)
-		wait_on_inode(inode);
+		inode_sync_wait(inode);
 	return ret;
 }
 EXPORT_SYMBOL(write_inode_now);
@@ -658,7 +667,7 @@ int generic_osync_inode(struct inode *in
 			err = err2;
 	}
 	else
-		wait_on_inode(inode);
+		inode_sync_wait(inode);
 
 	return err;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 86ec3f4..f9eb221 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1184,6 +1184,8 @@ #define I_FREEING		16
 #define I_CLEAR			32
 #define I_NEW			64
 #define I_WILL_FREE		128
+#define __I_SYNC		8
+#define I_SYNC			(1 << __I_SYNC) /* Currently being synced */
 
 #define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)
 
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index fc35e6b..3abc1d1 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -77,6 +77,13 @@ static inline void wait_on_inode(struct 
 	wait_on_bit(&inode->i_state, __I_LOCK, inode_wait,
 							TASK_UNINTERRUPTIBLE);
 }
+static inline void inode_sync_wait(struct inode *inode)
+{
+	might_sleep();
+	wait_on_bit(&inode->i_state, __I_SYNC, inode_wait,
+							TASK_UNINTERRUPTIBLE);
+}
+
 
 /*
  * mm/page-writeback.c
-- 
1.4.2.3