diff options
authorMike Snitzer <>2013-01-31 14:11:14 +0000
committerAlasdair G Kergon <>2013-01-31 14:11:14 +0000
commit0f640dca08330dfc7820d610578e5935b5e654b2 (patch)
parent949db153b6466c6f7cad5a427ecea94985927311 (diff)
dm thin: fix queue limits stacking
thin_io_hints() is blindly copying the queue limits from the thin-pool which can lead to incorrect limits being set. The fix here simply deletes the thin_io_hints() hook which leaves the existing stacking infrastructure to set the limits correctly. When a thin-pool uses an MD device for the data device a thin device from the thin-pool must respect MD's constraints about disallowing a bio from spanning multiple chunks. Otherwise we can see problems. If the raid0 chunksize is 1152K and thin-pool chunksize is 256K I see the following md/raid0 error (with extra debug tracing added to thin_endio) when mkfs.xfs is executed against the thin device: md/raid0:md99: make_request bug: can't convert block across chunks or bigger than 1152k 6688 127 device-mapper: thin: bio sector=2080 err=-5 bi_size=130560 bi_rw=17 bi_vcnt=32 bi_idx=0 This extra DM debugging shows that the failing bio is spanning across the first and second logical 1152K chunk (sector 2080 + 255 takes the bio beyond the first chunk's boundary of sector 2304). So the bio splitting that DM is doing clearly isn't respecting the MD limits. max_hw_sectors_kb is 127 for both the thin-pool and thin device (queue_max_hw_sectors returns 255 so we'll excuse sysfs's lack of precision). So this explains why bi_size is 130560. But the thin device's max_hw_sectors_kb should be 4 (PAGE_SIZE) given that it doesn't have a .merge function (for bio_add_page to consult indirectly via dm_merge_bvec) yet the thin-pool does sit above an MD device that has a compulsory merge_bvec_fn. This scenario is exactly why DM must resort to sending single PAGE_SIZE bios to the underlying layer. Some additional context for this is available in the header for commit 8cbeb67a ("dm: avoid unsupported spanning of md stripe boundaries"). Long story short, the reason a thin device doesn't properly get configured to have a max_hw_sectors_kb of 4 (PAGE_SIZE) is that thin_io_hints() is blindly copying the queue limits from the thin-pool device directly to the thin device's queue limits. Fix this by eliminating thin_io_hints. Doing so is safe because the block layer's queue limits stacking already enables the upper level thin device to inherit the thin-pool device's discard and minimum_io_size and optimal_io_size limits that get set in pool_io_hints. But avoiding the queue limits copy allows the thin and thin-pool limits to be different where it is important, namely max_hw_sectors_kb. Reported-by: Daniel Browning <> Signed-off-by: Mike Snitzer <> Cc: Signed-off-by: Alasdair G Kergon <>
1 files changed, 1 insertions, 12 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 675ae527401..5409607d487 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -2746,19 +2746,9 @@ static int thin_iterate_devices(struct dm_target *ti,
return 0;
- * A thin device always inherits its queue limits from its pool.
- */
-static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
- struct thin_c *tc = ti->private;
- *limits = bdev_get_queue(tc->pool_dev->bdev)->limits;
static struct target_type thin_target = {
.name = "thin",
- .version = {1, 6, 0},
+ .version = {1, 7, 0},
.module = THIS_MODULE,
.ctr = thin_ctr,
.dtr = thin_dtr,
@@ -2767,7 +2757,6 @@ static struct target_type thin_target = {
.postsuspend = thin_postsuspend,
.status = thin_status,
.iterate_devices = thin_iterate_devices,
- .io_hints = thin_io_hints,