dm thin: switch to an atomic_t for tracking pending new block preparations

Previously we used separate boolean values to track quiescing and
copying actions.  By switching to an atomic_t we can support blocks that
need a partial copy and partial zero.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 16 insertions, 13 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index fc9c848a60c9..4c9a3b5f4ff1 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -554,11 +554,16 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio,
 struct dm_thin_new_mapping {
         struct list_head list;
 
-        bool quiesced:1;
-        bool prepared:1;
         bool pass_discard:1;
         bool definitely_not_shared:1;
 
+        /*
+         * Track quiescing, copying and zeroing preparation actions.  When this
+         * counter hits zero the block is prepared and can be inserted into the
+         * btree.
+         */
+        atomic_t prepare_actions;
+
         int err;
         struct thin_c *tc;
         dm_block_t virt_block;
@@ -575,11 +580,11 @@ struct dm_thin_new_mapping {
         bio_end_io_t *saved_bi_end_io;
 };
 
-static void __maybe_add_mapping(struct dm_thin_new_mapping *m)
+static void __complete_mapping_preparation(struct dm_thin_new_mapping *m)
 {
         struct pool *pool = m->tc->pool;
 
-        if (m->quiesced && m->prepared) {
+        if (atomic_dec_and_test(&m->prepare_actions)) {
                 list_add_tail(&m->list, &pool->prepared_mappings);
                 wake_worker(pool);
         }
@@ -594,8 +599,7 @@ static void copy_complete(int read_err, unsigned long write_err, void *context)
         m->err = read_err || write_err ? -EIO : 0;
 
         spin_lock_irqsave(&pool->lock, flags);
-        m->prepared = true;
-        __maybe_add_mapping(m);
+        __complete_mapping_preparation(m);
         spin_unlock_irqrestore(&pool->lock, flags);
 }
 
@@ -609,8 +613,7 @@ static void overwrite_endio(struct bio *bio, int err)
         m->err = err;
 
         spin_lock_irqsave(&pool->lock, flags);
-        m->prepared = true;
-        __maybe_add_mapping(m);
+        __complete_mapping_preparation(m);
         spin_unlock_irqrestore(&pool->lock, flags);
 }
 
@@ -836,7 +839,9 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
         m->cell = cell;
 
         if (!dm_deferred_set_add_work(pool->shared_read_ds, &m->list))
-                m->quiesced = true;
+                atomic_set(&m->prepare_actions, 1); /* copy only */
+        else
+                atomic_set(&m->prepare_actions, 2); /* quiesce + copy */
 
         /*
          * IO to pool_dev remaps to the pool target's data_dev.
@@ -896,8 +901,7 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
         struct pool *pool = tc->pool;
         struct dm_thin_new_mapping *m = get_next_mapping(pool);
 
-        m->quiesced = true;
-        m->prepared = false;
+        atomic_set(&m->prepare_actions, 1); /* no need to quiesce */
         m->tc = tc;
         m->virt_block = virt_block;
         m->data_block = data_block;
@@ -3361,8 +3365,7 @@ static int thin_endio(struct dm_target *ti, struct bio *bio, int err)
                 spin_lock_irqsave(&pool->lock, flags);
                 list_for_each_entry_safe(m, tmp, &work, list) {
                         list_del(&m->list);
-                        m->quiesced = true;
-                        __maybe_add_mapping(m);
+                        __complete_mapping_preparation(m);
                 }
                 spin_unlock_irqrestore(&pool->lock, flags);
         }