mm: don't TestClearPageError in __filemap_fdatawait_range

The -EIO returned here can end up overriding whatever error is marked in
the address space, and be returned at fsync time, even when there is a
more appropriate error stored in the mapping.

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 that is silently discarded. Any subsystem that is relying on
PG_error to report errors during fsync can easily lose writeback errors
due to this. All you need is a stray sync() call to wait for writeback
to complete 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@redhat.com>

diff --git a/mm/filemap.c b/mm/filemap.c
index 49bc9720fb00bf22f126a0d28ed149f7ecdedb1d..eb99b5f23c617fb89040ce9fe54a6950d101a063 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -386,17 +386,16 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
-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) &&
@@ -413,14 +412,11 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
                                continue;
 
                        wait_on_page_writeback(page);
-                       if (TestClearPageError(page))
-                               ret = -EIO;
+                       ClearPageError(page);
                }
                pagevec_release(&pvec);
                cond_resched();
        }
-out:
-       return ret;
 }
 
 /**
@@ -440,14 +436,8 @@ out:
 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);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range);