introduce I_SYNC

I_LOCK was used for several unrelated purposes, which caused deadlock
situations in certain filesystems as a side effect.  One of the purposes
now uses the new I_SYNC bit.

Also document the various bits and change their order from historical to
logical.

[bunk@stusta.de: make fs/inode.c:wake_up_inode() static]
Signed-off-by: Joern Engel <joern@wohnheim.fh-wedel.de>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: David Chinner <dgc@sgi.com>
Cc: Anton Altaparmakov <aia21@cam.ac.uk>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 116 insertions, 42 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 71c158ac60a3..686734ff973d 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -100,11 +100,11 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                 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;
 
                 /*
@@ -172,6 +172,15 @@ static void requeue_io(struct inode *inode)
         list_move(&inode->i_list, &inode->i_sb->s_more_io);
 }
 
+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);
+}
+
 /*
  * Move expired dirty inodes from @delaying_queue to @dispatch_queue.
  */
@@ -225,11 +234,11 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
         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);
@@ -250,7 +259,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
         }
 
         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)) {
@@ -305,7 +314,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
                         list_move(&inode->i_list, &inode_unused);
                 }
         }
-        wake_up_inode(inode);
+        inode_sync_complete(inode);
         return ret;
 }
 
@@ -324,7 +333,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         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;
 
@@ -350,16 +359,16 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         /*
          * 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);
 }
@@ -392,7 +401,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
  * 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)
@@ -661,7 +670,7 @@ int write_inode_now(struct inode *inode, int sync)
         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);
@@ -736,7 +745,7 @@ int generic_osync_inode(struct inode *inode, struct address_space *mapping, int
                         err = err2;
         }
         else
-                wait_on_inode(inode);
+                inode_sync_wait(inode);
 
         return err;
 }
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 6bf6890f0530..0f5df73dbb73 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -384,7 +384,7 @@ static void hugetlbfs_forget_inode(struct inode *inode) __releases(inode_lock)
         struct super_block *sb = inode->i_sb;
 
         if (!hlist_unhashed(&inode->i_hash)) {
-                if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+                if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                         list_move(&inode->i_list, &inode_unused);
                 inodes_stat.nr_unused++;
                 if (!sb || (sb->s_flags & MS_ACTIVE)) {
diff --git a/fs/inode.c b/fs/inode.c
index c6165771e00e..ed35383d0b6c 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -99,6 +99,15 @@ struct inodes_stat_t inodes_stat;
 
 static struct kmem_cache * inode_cachep __read_mostly;
 
+static void wake_up_inode(struct inode *inode)
+{
+        /*
+         * Prevent speculative execution through spin_unlock(&inode_lock);
+         */
+        smp_mb();
+        wake_up_bit(&inode->i_state, __I_LOCK);
+}
+
 static struct inode *alloc_inode(struct super_block *sb)
 {
         static const struct address_space_operations empty_aops;
@@ -232,7 +241,7 @@ void __iget(struct inode * inode)
                 return;
         }
         atomic_inc(&inode->i_count);
-        if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+        if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                 list_move(&inode->i_list, &inode_in_use);
         inodes_stat.nr_unused--;
 }
@@ -253,7 +262,7 @@ void clear_inode(struct inode *inode)
         BUG_ON(inode->i_data.nrpages);
         BUG_ON(!(inode->i_state & I_FREEING));
         BUG_ON(inode->i_state & I_CLEAR);
-        wait_on_inode(inode);
+        inode_sync_wait(inode);
         DQUOT_DROP(inode);
         if (inode->i_sb->s_op->clear_inode)
                 inode->i_sb->s_op->clear_inode(inode);
@@ -1071,7 +1080,7 @@ static void generic_forget_inode(struct inode *inode)
         struct super_block *sb = inode->i_sb;
 
         if (!hlist_unhashed(&inode->i_hash)) {
-                if (!(inode->i_state & (I_DIRTY|I_LOCK)))
+                if (!(inode->i_state & (I_DIRTY|I_SYNC)))
                         list_move(&inode->i_list, &inode_unused);
                 inodes_stat.nr_unused++;
                 if (sb->s_flags & MS_ACTIVE) {
@@ -1314,15 +1323,6 @@ static void __wait_on_freeing_inode(struct inode *inode)
         spin_lock(&inode_lock);
 }
 
-void wake_up_inode(struct inode *inode)
-{
-        /*
-         * Prevent speculative execution through spin_unlock(&inode_lock);
-         */
-        smp_mb();
-        wake_up_bit(&inode->i_state, __I_LOCK);
-}
-
 /*
  * We rarely want to lock two inodes that do not have a parent/child
  * relationship (such as directory, child inode) simultaneously. The
diff --git a/fs/jfs/jfs_txnmgr.c b/fs/jfs/jfs_txnmgr.c
index 7aa1f7004eaf..e7c60ae6b5b2 100644
--- a/fs/jfs/jfs_txnmgr.c
+++ b/fs/jfs/jfs_txnmgr.c
@@ -1289,7 +1289,14 @@ int txCommit(tid_t tid,		/* transaction identifier */
                  * commit the transaction synchronously, so the last iput
                  * will be done by the calling thread (or later)
                  */
-                if (tblk->u.ip->i_state & I_LOCK)
+                /*
+                 * I believe this code is no longer needed.  Splitting I_LOCK
+                 * into two bits, I_LOCK and I_SYNC should prevent this
+                 * deadlock as well.  But since I don't have a JFS testload
+                 * to verify this, only a trivial s/I_LOCK/I_SYNC/ was done.
+                 * Joern
+                 */
+                if (tblk->u.ip->i_state & I_SYNC)
                         tblk->xflag &= ~COMMIT_LAZY;
         }
 
diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
index 0b5fa124bef2..e0e06dd4bef2 100644
--- a/fs/xfs/linux-2.6/xfs_iops.c
+++ b/fs/xfs/linux-2.6/xfs_iops.c
@@ -133,7 +133,7 @@ xfs_ichgtime(
          */
         SYNCHRONIZE();
         ip->i_update_core = 1;
-        if (!(inode->i_state & I_LOCK))
+        if (!(inode->i_state & I_SYNC))
                 mark_inode_dirty_sync(inode);
 }
 
@@ -185,7 +185,7 @@ xfs_ichgtime_fast(
          */
         SYNCHRONIZE();
         ip->i_update_core = 1;
-        if (!(inode->i_state & I_LOCK))
+        if (!(inode->i_state & I_SYNC))
                 mark_inode_dirty_sync(inode);
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b70331f9f5b7..365586a4c4de 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1261,16 +1261,68 @@ struct super_operations {
 #endif
 };
 
-/* Inode state bits.  Protected by inode_lock. */
-#define I_DIRTY_SYNC            1 /* Not dirty enough for O_DATASYNC */
-#define I_DIRTY_DATASYNC        2 /* Data-related inode changes pending */
-#define I_DIRTY_PAGES           4 /* Data-related inode changes pending */
-#define __I_LOCK                3
+/*
+ * Inode state bits.  Protected by inode_lock.
+ *
+ * Three bits determine the dirty state of the inode, I_DIRTY_SYNC,
+ * I_DIRTY_DATASYNC and I_DIRTY_PAGES.
+ *
+ * Four bits define the lifetime of an inode.  Initially, inodes are I_NEW,
+ * until that flag is cleared.  I_WILL_FREE, I_FREEING and I_CLEAR are set at
+ * various stages of removing an inode.
+ *
+ * Two bits are used for locking and completion notification, I_LOCK and I_SYNC.
+ *
+ * I_DIRTY_SYNC         Inode itself is dirty.
+ * I_DIRTY_DATASYNC     Data-related inode changes pending
+ * I_DIRTY_PAGES        Inode has dirty pages.  Inode itself may be clean.
+ * I_NEW                get_new_inode() sets i_state to I_LOCK|I_NEW.  Both
+ *                      are cleared by unlock_new_inode(), called from iget().
+ * I_WILL_FREE          Must be set when calling write_inode_now() if i_count
+ *                      is zero.  I_FREEING must be set when I_WILL_FREE is
+ *                      cleared.
+ * I_FREEING            Set when inode is about to be freed but still has dirty
+ *                      pages or buffers attached or the inode itself is still
+ *                      dirty.
+ * I_CLEAR              Set by clear_inode().  In this state the inode is clean
+ *                      and can be destroyed.
+ *
+ *                      Inodes that are I_WILL_FREE, I_FREEING or I_CLEAR are
+ *                      prohibited for many purposes.  iget() must wait for
+ *                      the inode to be completely released, then create it
+ *                      anew.  Other functions will just ignore such inodes,
+ *                      if appropriate.  I_LOCK is used for waiting.
+ *
+ * I_LOCK               Serves as both a mutex and completion notification.
+ *                      New inodes set I_LOCK.  If two processes both create
+ *                      the same inode, one of them will release its inode and
+ *                      wait for I_LOCK to be released before returning.
+ *                      Inodes in I_WILL_FREE, I_FREEING or I_CLEAR state can
+ *                      also cause waiting on I_LOCK, without I_LOCK actually
+ *                      being set.  find_inode() uses this to prevent returning
+ *                      nearly-dead inodes.
+ * I_SYNC               Similar to I_LOCK, but limited in scope to writeback
+ *                      of inode dirty data.  Having a seperate lock for this
+ *                      purpose reduces latency and prevents some filesystem-
+ *                      specific deadlocks.
+ *
+ * Q: Why does I_DIRTY_DATASYNC exist?  It appears as if it could be replaced
+ *    by (I_DIRTY_SYNC|I_DIRTY_PAGES).
+ * Q: What is the difference between I_WILL_FREE and I_FREEING?
+ * Q: igrab() only checks on (I_FREEING|I_WILL_FREE).  Should it also check on
+ *    I_CLEAR?  If not, why?
+ */
+#define I_DIRTY_SYNC            1
+#define I_DIRTY_DATASYNC        2
+#define I_DIRTY_PAGES           4
+#define I_NEW                   8
+#define I_WILL_FREE             16
+#define I_FREEING               32
+#define I_CLEAR                 64
+#define __I_LOCK                7
 #define I_LOCK                  (1 << __I_LOCK)
-#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)
 
 #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 1200868a5dee..bef7d66601cb 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -69,7 +69,6 @@ struct writeback_control {
  * fs/fs-writeback.c
  */     
 void writeback_inodes(struct writeback_control *wbc);
-void wake_up_inode(struct inode *inode);
 int inode_wait(void *);
 void sync_inodes_sb(struct super_block *, int wait);
 void sync_inodes(int wait);
@@ -81,6 +80,13 @@ static inline void wait_on_inode(struct inode *inode)
         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
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index bcdbbf6c4a85..d8c21e5a1bc9 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -37,7 +37,7 @@
 
 /*
  * The maximum number of pages to writeout in a single bdflush/kupdate
- * operation.  We do this so we don't hold I_LOCK against an inode for
+ * operation.  We do this so we don't hold I_SYNC against an inode for
  * enormous amounts of time, which would block a userspace task which has
  * been forced to throttle against that inode.  Also, the code reevaluates
  * the dirty each time it has written this many pages.