From e6e7ca92623a43156100306861272e04d46385fc Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Thu, 10 Sep 2020 08:26:17 -0700
Subject: [PATCH] iomap: Clear page error before beginning a write
Git-commit: e6e7ca92623a43156100306861272e04d46385fc
Patch-mainline: v5.10-rc1
References: bsc#1179683

If we find a page in write_begin which is !Uptodate, we need
to clear any error on the page before starting to read data
into it.  This matches how filemap_fault(), do_read_cache_page()
and generic_file_buffered_read() handle PageError on !Uptodate pages.
When calling iomap_set_range_uptodate() in __iomap_write_begin(), blocks
were not being marked as uptodate.

This was found with generic/127 and a specially modified kernel which
would fail (some) readahead I/Os.  The test read some bytes in a prior
page which caused readahead to extend into page 0x34.  There was
a subsequent write to page 0x34, followed by a read to page 0x34.
Because the blocks were still marked as !Uptodate, the read caused all
blocks to be re-read, overwriting the write.  With this change, and the
next one, the bytes which were written are marked as being Uptodate, so
even though the page is still marked as !Uptodate, the blocks containing
the written data are not re-read from storage.

Fixes: 9dc55f1389f9 ("iomap: add support for sub-pagesize buffered I/O without buffer heads")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/iomap/buffered-io.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288dba3f..c95454784df4 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -578,6 +578,7 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
 
 	if (PageUptodate(page))
 		return 0;
+	ClearPageError(page);
 
 	do {
 		iomap_adjust_read_range(inode, iop, &block_start,
-- 
2.16.4