[ 014/102] dm stripe: fix regression in stripe_width calculation

From: Greg Kroah-Hartman
Date: Fri May 17 2013 - 18:26:05 EST

3.9-stable review patch. If anyone has any objections, please let me know.


From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit d793e684277124d55c5d2444007e224635821346 upstream.

Fix a regression in the calculation of the stripe_width in the
dm stripe target which led to incorrect processing of device limits.

The stripe_width is the stripe device length divided by the number of
stripes. The group of commits in the range f14fa69 ("dm stripe: fix
size test") to eb850de ("dm stripe: support for non power of 2
chunksize") interfered with each other (a merging error) and led to the
stripe_width being set incorrectly to the stripe device length divided by
chunk_size * stripe_count.

For example, a stripe device's table with: 0 33553920 striped 3 512 ...
should result in a stripe_width of 11184640 (33553920 / 3), but due to
the bug it was getting set to 21845 (33553920 / (512 * 3)).

The impact of this bug is that device topologies that previously worked
fine with the stripe target are no longer considered valid. In
particular, there is a higher risk of seeing this issue if one of the
stripe devices has a 4K logical block size. Resulting in an error
message like this:
"device-mapper: table: 253:4: len=21845 not aligned to h/w logical block size 4096 of dm-1"

The fix is to swap the order of the divisions and to use a temporary
variable for the second one, so that width retains the intended

Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/md/dm-stripe.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -94,7 +94,7 @@ static int get_stripe(struct dm_target *
static int stripe_ctr(struct dm_target *ti, unsigned int argc, char **argv)
struct stripe_c *sc;
- sector_t width;
+ sector_t width, tmp_len;
uint32_t stripes;
uint32_t chunk_size;
int r;
@@ -116,15 +116,16 @@ static int stripe_ctr(struct dm_target *

width = ti->len;
- if (sector_div(width, chunk_size)) {
+ if (sector_div(width, stripes)) {
ti->error = "Target length not divisible by "
- "chunk size";
+ "number of stripes";
return -EINVAL;

- if (sector_div(width, stripes)) {
+ tmp_len = width;
+ if (sector_div(tmp_len, chunk_size)) {
ti->error = "Target length not divisible by "
- "number of stripes";
+ "chunk size";
return -EINVAL;

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