+ fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten.patch added to mm-hotfixes-unstable branch

+ fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Subject: fsdax: unshare: zero destination if srcmap is HOLE or UNWRITTEN
Date: Wed, 22 Mar 2023 11:11:09 +0000

unshare copies data from source to destination.  But if the source is HOLE
or UNWRITTEN extents, we should zero the destination, otherwise the result
will be unexpectable.

Link: https://lkml.kernel.org/r/1679483469-2-1-git-send-email-ruansy.fnst@fujitsu.com
Fixes: d984648e428b ("fsdax,xfs: port unshare to fsdax")
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/fs/dax.c~fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten
+++ a/fs/dax.c
@@ -1258,15 +1258,20 @@ static s64 dax_unshare_iter(struct iomap
 	/* don't bother with blocks that are not shared to start with */
 	if (!(iomap->flags & IOMAP_F_SHARED))
 		return length;
-	/* don't bother with holes or unwritten extents */
-	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
-		return length;
 
 	id = dax_read_lock();
 	ret = dax_iomap_direct_access(iomap, pos, length, &daddr, NULL);
 	if (ret < 0)
 		goto out_unlock;
 
+	/* zero the distance if srcmap is HOLE or UNWRITTEN */
+	if (srcmap->flags & IOMAP_F_SHARED || srcmap->type == IOMAP_UNWRITTEN) {
+		memset(daddr, 0, length);
+		dax_flush(iomap->dax_dev, daddr, length);
+		ret = length;
+		goto out_unlock;
+	}
+
 	ret = dax_iomap_direct_access(srcmap, pos, length, &saddr, NULL);
 	if (ret < 0)
 		goto out_unlock;
_

Patches currently in -mm which might be from ruansy.fnst@fujitsu.com are

fsdax-unshare-zero-destination-if-srcmap-is-hole-or-unwritten.patch