dm: always manage discard support in terms of max_hw_discard_sectors

Commit 4f563a64 ("block: add a max_user_discard_sectors queue
limit") changed block core to set max_discard_sectors to:
 min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors)

Since commit 1c0e7202 ("dm: use queue_limits_set") it was reported
dm-thinp was failing in a few fstests (generic/347 and generic/405)
with the first WARN_ON_ONCE in dm_cell_key_has_valid_range() being
reported, e.g.:
WARNING: CPU: 1 PID: 30 at drivers/md/dm-bio-prison-v1.c:128 dm_cell_key_has_valid_range+0x3d/0x50

blk_set_stacking_limits() sets max_user_discard_sectors to UINT_MAX,
so given how block core now sets max_discard_sectors (detailed above)
it follows that blk_stack_limits() stacks up the underlying device's
max_hw_discard_sectors and max_discard_sectors is set to match it. If
max_hw_discard_sectors exceeds dm's BIO_PRISON_MAX_RANGE, then
dm_cell_key_has_valid_range() will trigger the warning with:
WARN_ON_ONCE(key->block_end - key->block_begin > BIO_PRISON_MAX_RANGE)

Aside from this warning, the discard will fail.  Fix this and other DM
issues by governing discard support in terms of max_hw_discard_sectors
instead of max_discard_sectors.
Reported-by: Theodore Ts'o <tytso@mit.edu>
Fixes: 1c0e7202 ("dm: use queue_limits_set")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-cache-target.c

@@ -3394,8 +3394,8 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
 
 	if (!cache->features.discard_passdown) {
 		/* No passdown is done so setting own virtual limits */
-		limits->max_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
-						    cache->origin_sectors);
+		limits->max_hw_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
+						       cache->origin_sectors);
 		limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
 		return;
 	}
@@ -3404,7 +3404,6 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
 	 * cache_iterate_devices() is stacking both origin and fast device limits
 	 * but discards aren't passed to fast device, so inherit origin's limits.
 	 */
-	limits->max_discard_sectors = origin_limits->max_discard_sectors;
 	limits->max_hw_discard_sectors = origin_limits->max_hw_discard_sectors;
 	limits->discard_granularity = origin_limits->discard_granularity;
 	limits->discard_alignment = origin_limits->discard_alignment;

drivers/md/dm-clone-target.c

@@ -2050,7 +2050,8 @@ static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
 	if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags)) {
 		/* No passdown is done so we set our own virtual limits */
 		limits->discard_granularity = clone->region_size << SECTOR_SHIFT;
-		limits->max_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT, clone->region_size);
+		limits->max_hw_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT,
+							    clone->region_size);
 		return;
 	}
 
@@ -2059,7 +2060,6 @@ static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
 	 * device limits but discards aren't passed to the source device, so
 	 * inherit destination's limits.
 	 */
-	limits->max_discard_sectors = dest_limits->max_discard_sectors;
 	limits->max_hw_discard_sectors = dest_limits->max_hw_discard_sectors;
 	limits->discard_granularity = dest_limits->discard_granularity;
 	limits->discard_alignment = dest_limits->discard_alignment;

drivers/md/dm-log-writes.c

@@ -871,7 +871,7 @@ static void log_writes_io_hints(struct dm_target *ti, struct queue_limits *limit
 	if (!bdev_max_discard_sectors(lc->dev->bdev)) {
 		lc->device_supports_discard = false;
 		limits->discard_granularity = lc->sectorsize;
-		limits->max_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
+		limits->max_hw_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
 	}
 	limits->logical_block_size = bdev_logical_block_size(lc->dev->bdev);
 	limits->physical_block_size = bdev_physical_block_size(lc->dev->bdev);

drivers/md/dm-snap.c

@@ -2410,7 +2410,7 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 		/* All discards are split on chunk_size boundary */
 		limits->discard_granularity = snap->store->chunk_size;
-		limits->max_discard_sectors = snap->store->chunk_size;
+		limits->max_hw_discard_sectors = snap->store->chunk_size;
 
 		up_read(&_origins_lock);
 	}

drivers/md/dm-target.c

@@ -249,7 +249,6 @@ static int io_err_iterate_devices(struct dm_target *ti,
 
 static void io_err_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
-	limits->max_discard_sectors = UINT_MAX;
 	limits->max_hw_discard_sectors = UINT_MAX;
 	limits->discard_granularity = 512;
 }

drivers/md/dm-thin.c

@@ -4100,7 +4100,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	if (pt->adjusted_pf.discard_enabled) {
 		disable_discard_passdown_if_not_supported(pt);
 		if (!pt->adjusted_pf.discard_passdown)
-			limits->max_discard_sectors = 0;
+			limits->max_hw_discard_sectors = 0;
 		/*
 		 * The pool uses the same discard limits as the underlying data
 		 * device.  DM core has already set this up.
@@ -4497,7 +4497,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	if (pool->pf.discard_enabled) {
 		limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
-		limits->max_discard_sectors = pool->sectors_per_block * BIO_PRISON_MAX_RANGE;
+		limits->max_hw_discard_sectors = pool->sectors_per_block * BIO_PRISON_MAX_RANGE;
 	}
 }
 

drivers/md/dm-zero.c

@@ -61,7 +61,6 @@ static int zero_map(struct dm_target *ti, struct bio *bio)
 
 static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
-	limits->max_discard_sectors = UINT_MAX;
 	limits->max_hw_discard_sectors = UINT_MAX;
 	limits->discard_granularity = 512;
 }

drivers/md/dm-zoned-target.c

@@ -1001,7 +1001,6 @@ static void dmz_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	limits->discard_alignment = 0;
 	limits->discard_granularity = DMZ_BLOCK_SIZE;
-	limits->max_discard_sectors = chunk_sectors;
 	limits->max_hw_discard_sectors = chunk_sectors;
 	limits->max_write_zeroes_sectors = chunk_sectors;
 

drivers/md/dm.c

@@ -1086,7 +1086,7 @@ void disable_discard(struct mapped_device *md)
 	struct queue_limits *limits = dm_get_queue_limits(md);
 
 	/* device doesn't really support DISCARD, disable it */
-	limits->max_discard_sectors = 0;
+	limits->max_hw_discard_sectors = 0;
 }
 
 void disable_write_zeroes(struct mapped_device *md)