[patch 30/40] mm: write_cache_pages writepage error fix

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Nick Piggin <npiggin@xxxxxxx>

commit 00266770b8b3a6a77f896ca501a0613739086832 upstream.

In write_cache_pages, if ret signals a real error, but we still have some
pages left in the pagevec, done would be set to 1, but the remaining pages
would continue to be processed and ret will be overwritten in the process.

It could easily be overwritten with success, and thus success will be
returned even if there is an error.  Thus the caller is told all writes
succeeded, wheras in reality some did not.

Fix this by bailing immediately if there is an error, and retaining the
first error code.

This is a data integrity bug.

Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Cc: Chris Mason <chris.mason@xxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/page-writeback.c |   25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -948,11 +948,26 @@ retry:
 
 			ret = (*writepage)(page, wbc, data);
 
-			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE)) {
-				unlock_page(page);
-				ret = 0;
-			}
-			if (ret || (--(wbc->nr_to_write) <= 0))
+			if (unlikely(ret)) {
+				if (ret == AOP_WRITEPAGE_ACTIVATE) {
+					unlock_page(page);
+					ret = 0;
+				} else {
+					/*
+					 * done_index is set past this page,
+					 * so media errors will not choke
+					 * background writeout for the entire
+					 * file. This has consequences for
+					 * range_cyclic semantics (ie. it may
+					 * not be suitable for data integrity
+					 * writeout).
+					 */
+					done = 1;
+					break;
+				}
+ 			}
+
+			if (--(wbc->nr_to_write) <= 0)
 				done = 1;
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;

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