dm: make sure to obey max_io_len_target_boundary [Linux 5.2]

dm: make sure to obey max_io_len_target_boundary [Linux 5.2]

This Linux kernel change "dm: make sure to obey max_io_len_target_boundary" is included in the Linux 5.2 release. This change is authored by Michael Lass <bevan [at] bi-co.net> on Tue May 21 21:58:07 2019 +0200. The commit for this change in Linux stable tree is 51b86f9 (patch).

dm: make sure to obey max_io_len_target_boundary

Commit 61697a6abd24 ("dm: eliminate 'split_discard_bios' flag from DM
target interface") incorrectly removed code from
__send_changing_extent_only() that is required to impose a per-target IO
boundary on IO that exceeds max_io_len_target_boundary().  Otherwise
"special" IO (e.g. DISCARD, WRITE SAME, WRITE ZEROES) can write beyond
where allowed.

Fix this by restoring the max_io_len_target_boundary() limit in
__send_changing_extent_only()

Fixes: 61697a6abd24 ("dm: eliminate 'split_discard_bios' flag from DM target interface")
Cc: [email protected] # 5.1+
Signed-off-by: Michael Lass <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/md/dm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 1fb1333..997385c 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1469,7 +1469,7 @@ static unsigned get_num_write_zeroes_bios(struct dm_target *ti)
 static int __send_changing_extent_only(struct clone_info *ci, struct dm_target *ti,
                       unsigned num_bios)
 {
-   unsigned len = ci->sector_count;
+   unsigned len;

    /*
     * Even though the device advertised support for this type of
@@ -1480,6 +1480,8 @@ static int __send_changing_extent_only(struct clone_info *ci, struct dm_target *
    if (!num_bios)
        return -EOPNOTSUPP;

+   len = min((sector_t)ci->sector_count, max_io_len_target_boundary(ci->sector, ti));
+
    __send_duplicate_bios(ci, ti, num_bios, &len);

    ci->sector += len;

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