[PATCH] fix inode state corruption (2.6.8-rc1-bk1)

[Miklos Szeredi]

Hi Andrew,

This patch fixes a hard-to-trigger condition, where the inode is on
the inode_in_use list while it's state is dirty.  In this state dirty
pages are not written back in sync() or from kupdate, only from direct
page reclaim.  And this causes a livelock in balance_dirty_pages after
a while.

Please apply!

The actual sequence of events required to get into this state is:

thread   function                             inode state         inode list
----------------------------------------------------------------------------
1 __sync_single_inode (background)            I_DIRTY             sb->s_io
1 do_writepages ...                           I_LOCKED
2 __writeback_single_inode (sync) sleeps      I_LOCKED
1 __sync_single_inode (background) finish     0                   inode_in_use
2 __writeback_single_inode (sync) wakeup      0
2 __sync_single_inode (sync)                  0  
2 do_writepages ...                           I_LOCKED
3 __mark_inode_dirty                          I_LOCKED | I_DIRTY
2 __sync_single_inode (sync) finish           I_DIRTY             left on
                                                                  inode_in_use

Signed-off-by: Miklos Szeredi <miklos@xxxxxxxxxx>

==============================================================================
--- linux-2.6.8-rc1-bk1/fs/fs-writeback.c.orig	2004-07-13 12:59:58.000000000 +0200
+++ linux-2.6.8-rc1-bk1/fs/fs-writeback.c	2004-07-13 14:31:07.000000000 +0200
@@ -213,8 +213,17 @@ __sync_single_inode(struct inode *inode,
 		} else if (inode->i_state & I_DIRTY) {
 			/*
 			 * Someone redirtied the inode while were writing back
-			 * the pages: nothing to do.
+			 * the pages.
 			 */
+			if (wait) {
+				/*
+				 * It is possible that this function is entered
+				 * with the inode on the in_use list, and it
+				 * is dirtied during being locked, in which
+				 * case it must be moved onto the dirty list.
+				 */
+				list_move(&inode->i_list, &sb->s_dirty);
+			}
 		} else if (atomic_read(&inode->i_count)) {
 			/*
 			 * The inode is clean, inuse
-
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