[PATCH 3.12 055/235] md/raid5: limit request size according to implementation limits

From: Jiri Slaby
Date: Fri Jan 27 2017 - 06:04:37 EST

From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>

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


commit e8d7c33232e5fdfa761c3416539bc5b4acd12db5 upstream.

Current implementation employ 16bit counter of active stripes in lower
bits of bio->bi_phys_segments. If request is big enough to overflow
this counter bio will be completed and freed too early.

Fortunately this not happens in default configuration because several
other limits prevent that: stripe_cache_size * nr_disks effectively
limits count of active stripes. And small max_sectors_kb at lower
disks prevent that during normal read/write operations.

Overflow easily happens in discard if it's enabled by module parameter
"devices_handle_discard_safely" and stripe_cache_size is set big enough.

This patch limits requests size with 256Mb - 8Kb to prevent overflows.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Neil Brown <neilb@xxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
drivers/md/raid5.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 9fbc77c6e132..01757b23e1fc 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5943,6 +5943,15 @@ static int run(struct mddev *mddev)
stripe = (stripe | (stripe-1)) + 1;
mddev->queue->limits.discard_alignment = stripe;
mddev->queue->limits.discard_granularity = stripe;
+ /*
+ * We use 16-bit counter of active stripes in bi_phys_segments
+ * (minus one for over-loaded initialization)
+ */
+ blk_queue_max_hw_sectors(mddev->queue, 0xfffe * STRIPE_SECTORS);
+ blk_queue_max_discard_sectors(mddev->queue,
+ 0xfffe * STRIPE_SECTORS);
* unaligned part of discard request will be ignored, so can't
* guarantee discard_zeroes_data