On Tue, Aug 03, 2010 at 09:22:16PM +0800, Wu Fengguang wrote:

quoted

quoted

  Fengguang, how about merging also the attached simple patch together with
my fix? With these two patches, I'm not able to trigger any sync livelock
while without one of them I hit them quite easily...

This looks OK. However note that redirty_tail() can modify
dirtied_when unexpectedly. So the more we rely on wb_start, the more
possibility an inode is (wrongly) skipped by sync. I have a bunch of
patches to remove redirty_tail(). However they may not be good
candidates for 2.6.36..

It looks that setting wb_start at the beginning of
writeback_inodes_wb() won't be easily affected by redirty_tail().

Except for this redirty_tail(), which may mess up the dirtied_when
ordering in b_dirty and later on break the assumption of
inode_dirtied_after(inode, wbc->wb_start).

It can be replaced by a requeue_io() for now.  Christoph mentioned a
patchset to introduce sb->s_wb, which should be a better solution.

Thanks,
Fengguang

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index a178828..e56e68b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c

@@ -457,12 +457,7 @@ int generic_writeback_sb_inodes(struct super_block *sb,
 
 		if (inode->i_sb != sb) {
 			if (only_this_sb) {
-				/*
-				 * We only want to write back data for this
-				 * superblock, move all inodes not belonging
-				 * to it back onto the dirty list.
-				 */
-				redirty_tail(inode);
+				requeue_io(inode);
 				continue;
 			}
 

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