dm thin: remove cells from stack

This patch takes advantage of the new bio-prison interface where the
memory is now passed in rather than using a mempool in bio-prison.
This allows the map function to avoid performing potentially-blocking
allocations that could lead to deadlocks: We want to avoid the cell
allocation that is done in bio_detain.

(The potential for mempool deadlocks still remains in other functions
that use bio_detain.)

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 32 insertions, 15 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 5304e3a29a14..009339d62828 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -229,6 +229,17 @@ struct thin_c {
 
 /*----------------------------------------------------------------*/
 
+/*
+ * wake_worker() is used when new work is queued and when pool_resume is
+ * ready to continue deferred IO processing.
+ */
+static void wake_worker(struct pool *pool)
+{
+        queue_work(pool->wq, &pool->worker);
+}
+
+/*----------------------------------------------------------------*/
+
 static int bio_detain(struct pool *pool, struct dm_cell_key *key, struct bio *bio,
                       struct dm_bio_prison_cell **cell_result)
 {
@@ -268,6 +279,19 @@ static void cell_release_no_holder(struct pool *pool,
         dm_bio_prison_free_cell(pool->prison, cell);
 }
 
+static void cell_defer_no_holder_no_free(struct thin_c *tc,
+                                         struct dm_bio_prison_cell *cell)
+{
+        struct pool *pool = tc->pool;
+        unsigned long flags;
+
+        spin_lock_irqsave(&pool->lock, flags);
+        dm_cell_release_no_holder(pool->prison, cell, &pool->deferred_bios);
+        spin_unlock_irqrestore(&pool->lock, flags);
+
+        wake_worker(pool);
+}
+
 static void cell_error(struct pool *pool,
                        struct dm_bio_prison_cell *cell)
 {
@@ -477,15 +501,6 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio,
         issue(tc, bio);
 }
 
-/*
- * wake_worker() is used when new work is queued and when pool_resume is
- * ready to continue deferred IO processing.
- */
-static void wake_worker(struct pool *pool)
-{
-        queue_work(pool->wq, &pool->worker);
-}
-
 /*----------------------------------------------------------------*/
 
 /*
@@ -601,6 +616,7 @@ static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
         list_del(&m->list);
         mempool_free(m, m->tc->pool->mapping_pool);
 }
+
 static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 {
         struct thin_c *tc = m->tc;
@@ -1438,7 +1454,8 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
         dm_block_t block = get_bio_block(tc, bio);
         struct dm_thin_device *td = tc->td;
         struct dm_thin_lookup_result result;
-        struct dm_bio_prison_cell *cell1, *cell2;
+        struct dm_bio_prison_cell cell1, cell2;
+        struct dm_bio_prison_cell *cell_result;
         struct dm_cell_key key;
 
         thin_hook_bio(tc, bio);
@@ -1480,18 +1497,18 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                 }
 
                 build_virtual_key(tc->td, block, &key);
-                if (bio_detain(tc->pool, &key, bio, &cell1))
+                if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
                         return DM_MAPIO_SUBMITTED;
 
                 build_data_key(tc->td, result.block, &key);
-                if (bio_detain(tc->pool, &key, bio, &cell2)) {
-                        cell_defer_no_holder(tc, cell1);
+                if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2, &cell_result)) {
+                        cell_defer_no_holder_no_free(tc, &cell1);
                         return DM_MAPIO_SUBMITTED;
                 }
 
                 inc_all_io_entry(tc->pool, bio);
-                cell_defer_no_holder(tc, cell2);
-                cell_defer_no_holder(tc, cell1);
+                cell_defer_no_holder_no_free(tc, &cell2);
+                cell_defer_no_holder_no_free(tc, &cell1);
 
                 remap(tc, bio, result.block);
                 return DM_MAPIO_REMAPPED;