[PATCH 5/5] writeback: check skipped pages on WB_SYNC_ALL

[Wu Fengguang]

In WB_SYNC_ALL mode, filesystems are not expected to skip dirty pages on
temporal lock contentions or non fatal errors, otherwise sync() will
return without actually syncing the skipped pages. Add a check to
catch possible redirty_page_for_writepage() callers that violate this
expectation.

I'd recommend to keep this check in -mm tree for some time and fixup the
possible warnings before pushing it to upstream.

Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/fs-writeback.c |    1 +
 1 file changed, 1 insertion(+)

--- linux-next.orig/fs/fs-writeback.c	2010-11-07 22:01:06.000000000 +0800
+++ linux-next/fs/fs-writeback.c	2010-11-07 22:01:15.000000000 +0800
@@ -527,6 +527,7 @@ static int writeback_sb_inodes(struct su
 			 * buffers.  Skip this inode for now.
 			 */
 			redirty_tail(inode);
+			WARN_ON_ONCE(wbc->sync_mode == WB_SYNC_ALL);
 		}
 		spin_unlock(&inode_lock);
 		iput(inode);


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