Commit 5e8fcc1a authored Jul 06, 2017 by Jeff Layton

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>

parent cbeaf951

mm/filemap.c

+5 −15

Original line number	Diff line number	Diff line
		@@ -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);

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