[PATCH] clear PageError bit in msync & fsync

[Rik van Riel]

Temporary IO failures, eg. due to loss of both multipath paths, can
permanently leave the PageError bit set on a page, resulting in
msync or fsync returning -EIO over and over again, even if IO is
now getting to the disk correctly.

We already clear the AS_ENOSPC and AS_IO bits in mapping->flags in
the filemap_fdatawait_range function.  Also clearing the PageError
bit on the page allows subsequent msync or fsync calls on this file
to return without an error, if the subsequent IO succeeds.

Unfortunately data written out in the msync or fsync call that
returned -EIO can still get lost, because the page dirty bit appears
to not get restored on IO error.  However, the alternative could be
potentially all of memory filling up with uncleanable dirty pages,
hanging the system, so there is no nice choice here...

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 5f38c46..4805fde 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -198,7 +198,7 @@ static inline int __TestClearPage##uname(struct page *page) { return 0; }
 struct page;	/* forward declaration */
 
 TESTPAGEFLAG(Locked, locked) TESTSETFLAG(Locked, locked)
-PAGEFLAG(Error, error)
+PAGEFLAG(Error, error) TESTCLEARFLAG(Error, error)
 PAGEFLAG(Referenced, referenced) TESTCLEARFLAG(Referenced, referenced)
 PAGEFLAG(Dirty, dirty) TESTSCFLAG(Dirty, dirty) __CLEARPAGEFLAG(Dirty, dirty)
 PAGEFLAG(LRU, lru) __CLEARPAGEFLAG(LRU, lru)
diff --git a/mm/filemap.c b/mm/filemap.c
index 61ba5e4..ba27b83 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -296,7 +296,7 @@ int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
 				continue;
 
 			wait_on_page_writeback(page);
-			if (PageError(page))
+			if (TestClearPageError(page))
 				ret = -EIO;
 		}
 		pagevec_release(&pvec);

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