[PATCH v2 8/9] mm: don't TestClearPageError in __filemap_fdatawait_range

From: Jeff Layton
Date: Wed Mar 08 2017 - 11:42:30 EST

The -EIO returned here can end up overriding whatever error is marked in
the address space. This means that an -ENOSPC error (AS_ENOSPC) can end
up being turned into -EIO if a page gets PG_error set on it during error

Read errors are also sometimes tracked on a per-page level using
PG_error. Suppose we have a read error on a page, and then that page is
subsequently dirtied by overwriting the whole page. Writeback doesn't
clear PG_error, so we can then end up successfully writing back that
page and still return -EIO on fsync.

Worse yet, PG_error is cleared during a sync() syscall, but the -EIO
return from this code is silently discarded. Any subsystem that is
relying on PG_error to report errors during fsync or close is already
broken due to this. All you need is a stray sync() call on the box
at the wrong time and you've lost the error.

Since the handling of the PG_error flag is somewhat inconsistent across
subsystems, let's just rely on marking the address space when there are
writeback errors. Change the TestClearPageError call to ClearPageError,
and make __filemap_fdatawait_range a void return function.

Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
mm/filemap.c | 20 +++++---------------
1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index fc123b9833e1..150559e94f8a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -376,17 +376,16 @@ int filemap_flush(struct address_space *mapping)

-static int __filemap_fdatawait_range(struct address_space *mapping,
+static void __filemap_fdatawait_range(struct address_space *mapping,
loff_t start_byte, loff_t end_byte)
pgoff_t index = start_byte >> PAGE_SHIFT;
pgoff_t end = end_byte >> PAGE_SHIFT;
struct pagevec pvec;
int nr_pages;
- int ret = 0;

if (end_byte < start_byte)
- goto out;
+ return;

pagevec_init(&pvec, 0);
while ((index <= end) &&
@@ -403,14 +402,11 @@ static int __filemap_fdatawait_range(struct address_space *mapping,

- if (TestClearPageError(page))
- ret = -EIO;
+ ClearPageError(page);
- return ret;

@@ -430,14 +426,8 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
loff_t end_byte)
- int ret, ret2;
- ret = __filemap_fdatawait_range(mapping, start_byte, end_byte);
- ret2 = filemap_check_errors(mapping);
- if (!ret)
- ret = ret2;
- return ret;
+ __filemap_fdatawait_range(mapping, start_byte, end_byte);
+ return filemap_check_errors(mapping);