iomap: Mark read blocks uptodate in write_begin

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>

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index c954547..897ab9a 100644 (file)
--- 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;