Patch "iomap: Mark read blocks uptodate in write_begin" has been added to the 5.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    iomap: Mark read blocks uptodate in write_begin

to the 5.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     iomap-mark-read-blocks-uptodate-in-write_begin.patch
and it can be found in the queue-5.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 072240c3f55268439b4493d4949839fde6599bdd
Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Date:   Thu Sep 10 08:26:18 2020 -0700

    iomap: Mark read blocks uptodate in write_begin
    
    [ 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@xxxxxxxxxxxxx>
    Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
    Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
    Reviewed-by: Christoph Hellwig <hch@xxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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;