From: Matthew Wilcox (Oracle) willy@infradead.org
[ Upstream commit e6e7ca92623a43156100306861272e04d46385fc ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 bcfc288dba3fb..c95454784df48 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,