1 files changed, 57 insertions, 30 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index e99f4134dbd7..c29410af1e22 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -580,7 +580,8 @@ struct pool_c {
         struct dm_target_callbacks callbacks;
 
         dm_block_t low_water_blocks;
-        struct pool_features pf;
+        struct pool_features requested_pf; /* Features requested during table load */
+        struct pool_features adjusted_pf;  /* Features used after adjusting for constituent devices */
 };
 
 /*
@@ -1848,21 +1849,36 @@ static bool data_dev_supports_discard(struct pool_c *pt)
 
 /*
  * If discard_passdown was enabled verify that the data device
- * supports discards.  Disable discard_passdown if not; otherwise
- * -EOPNOTSUPP will be returned.
+ * supports discards.  Disable discard_passdown if not.
  */
-static void disable_passdown_if_not_supported(struct pool_c *pt,
-                                              struct pool_features *pf)
+static void disable_passdown_if_not_supported(struct pool_c *pt)
 {
+        struct pool *pool = pt->pool;
+        struct block_device *data_bdev = pt->data_dev->bdev;
+        struct queue_limits *data_limits = &bdev_get_queue(data_bdev)->limits;
+        sector_t block_size = pool->sectors_per_block << SECTOR_SHIFT;
+        const char *reason = NULL;
         char buf[BDEVNAME_SIZE];
 
-        if (!pf->discard_passdown || data_dev_supports_discard(pt))
+        if (!pt->adjusted_pf.discard_passdown)
                 return;
 
-        DMWARN("Discard unsupported by data device (%s): Disabling discard passdown.",
-               bdevname(pt->data_dev->bdev, buf));
+        if (!data_dev_supports_discard(pt))
+                reason = "discard unsupported";
+
+        else if (data_limits->max_discard_sectors < pool->sectors_per_block)
+                reason = "max discard sectors smaller than a block";
 
-        pf->discard_passdown = false;
+        else if (data_limits->discard_granularity > block_size)
+                reason = "discard granularity larger than a block";
+
+        else if (block_size & (data_limits->discard_granularity - 1))
+                reason = "discard granularity not a factor of block size";
+
+        if (reason) {
+                DMWARN("Data device (%s) %s: Disabling discard passdown.", bdevname(data_bdev, buf), reason);
+                pt->adjusted_pf.discard_passdown = false;
+        }
 }
 
 static int bind_control_target(struct pool *pool, struct dm_target *ti)
@@ -1873,16 +1889,15 @@ static int bind_control_target(struct pool *pool, struct dm_target *ti)
          * We want to make sure that degraded pools are never upgraded.
          */
         enum pool_mode old_mode = pool->pf.mode;
-        enum pool_mode new_mode = pt->pf.mode;
+        enum pool_mode new_mode = pt->adjusted_pf.mode;
 
         if (old_mode > new_mode)
                 new_mode = old_mode;
 
         pool->ti = ti;
         pool->low_water_blocks = pt->low_water_blocks;
-        pool->pf = pt->pf;
+        pool->pf = pt->adjusted_pf;
 
-        disable_passdown_if_not_supported(pt, &pool->pf);
         set_pool_mode(pool, new_mode);
 
         return 0;
@@ -2271,7 +2286,7 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
         pt->metadata_dev = metadata_dev;
         pt->data_dev = data_dev;
         pt->low_water_blocks = low_water_blocks;
-        pt->pf = pf;
+        pt->adjusted_pf = pt->requested_pf = pf;
         ti->num_flush_requests = 1;
 
         /*
@@ -2718,7 +2733,7 @@ static int pool_status(struct dm_target *ti, status_type_t type,
                        format_dev_t(buf2, pt->data_dev->bdev->bd_dev),
                        (unsigned long)pool->sectors_per_block,
                        (unsigned long long)pt->low_water_blocks);
-                emit_flags(&pt->pf, result, sz, maxlen);
+                emit_flags(&pt->requested_pf, result, sz, maxlen);
                 break;
         }
 
@@ -2747,19 +2762,21 @@ static int pool_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
         return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
 }
 
-static void set_discard_limits(struct pool *pool, struct queue_limits *limits)
+static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits)
 {
-        /*
-         * FIXME: these limits may be incompatible with the pool's data device
-         */
+        struct pool *pool = pt->pool;
+        struct queue_limits *data_limits;
+
         limits->max_discard_sectors = pool->sectors_per_block;
 
         /*
-         * This is just a hint, and not enforced.  We have to cope with
-         * bios that cover a block partially.  A discard that spans a block
-         * boundary is not sent to this target.
+         * discard_granularity is just a hint, and not enforced.
          */
-        limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
+        if (pt->adjusted_pf.discard_passdown) {
+                data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
+                limits->discard_granularity = data_limits->discard_granularity;
+        } else
+                limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
 }
 
 static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
@@ -2769,15 +2786,25 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
         blk_limits_io_min(limits, 0);
         blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
-        if (pool->pf.discard_enabled)
-                set_discard_limits(pool, limits);
+
+        /*
+         * pt->adjusted_pf is a staging area for the actual features to use.
+         * They get transferred to the live pool in bind_control_target()
+         * called from pool_preresume().
+         */
+        if (!pt->adjusted_pf.discard_enabled)
+                return;
+
+        disable_passdown_if_not_supported(pt);
+
+        set_discard_limits(pt, limits);
 }
 
 static struct target_type pool_target = {
         .name = "thin-pool",
         .features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
                     DM_TARGET_IMMUTABLE,
-        .version = {1, 3, 0},
+        .version = {1, 4, 0},
         .module = THIS_MODULE,
         .ctr = pool_ctr,
         .dtr = pool_dtr,
@@ -3056,19 +3083,19 @@ 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;
-        struct pool *pool = tc->pool;
 
-        blk_limits_io_min(limits, 0);
-        blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
-        set_discard_limits(pool, limits);
+        *limits = bdev_get_queue(tc->pool_dev->bdev)->limits;
 }
 
 static struct target_type thin_target = {
         .name = "thin",
-        .version = {1, 3, 0},
+        .version = {1, 4, 0},
         .module = THIS_MODULE,
         .ctr = thin_ctr,
         .dtr = thin_dtr,