[PATCH 5.9 250/757] iomap: Mark read blocks uptodate in write_begin

Greg Kroah-Hartman
2020-10-27T15:56:54Z

From: Matthew Wilcox (Oracle) <willy@infradead.org>

[ Upstream commit 14284fedf59f1647264f4603d64418cf1fcd3eb0 ]

When bringing (portions of) a page uptodate, we were marking blocks that
were zeroed as being uptodate, but not blocks that were read from storage.

Like the previous commit, this problem was found with generic/127 and
a kernel which failed readahead I/Os. This bug causes writes to be
silently lost when working with flaky 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 | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index c95454784df48..897ab9a26a74c 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -574,7 +574,6 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
loff_t block_start = pos & ~(block_size - 1);
loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1);
unsigned from = offset_in_page(pos), to = from + len, poff, plen;
- int status;

if (PageUptodate(page))
return 0;
@@ -595,14 +594,13 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
if (WARN_ON_ONCE(flags & IOMAP_WRITE_F_UNSHARE))
return -EIO;
zero_user_segments(page, poff, from, to, poff + plen);
- iomap_set_range_uptodate(page, poff, plen);
- continue;
+ } else {
+ int status = iomap_read_page_sync(block_start, page,
+ poff, plen, srcmap);
+ if (status)
+ return status;
}
-
- status = iomap_read_page_sync(block_start, page, poff, plen,
- srcmap);
- if (status)
- return status;
+ iomap_set_range_uptodate(page, poff, plen);
} while ((block_start += plen) < block_end);

return 0;
--
2.25.1