bcache: Fix moving_gc deadlocking with a foreground write

Deadlock happened because a foreground write slept, waiting for a bucket
to be allocated. Normally the gc would mark buckets available for invalidation.
But the moving_gc was stuck waiting for outstanding writes to complete.
These writes used the bcache_wq, the same queue foreground writes used.

This fix gives moving_gc its own work queue, so it was still finish moving
even if foreground writes are stuck waiting for allocation. It also makes
work queue a parameter to the data_insert path, so moving_gc can use its
workqueue for writes.

Signed-off-by: Nicholas Swenson <nks@daterainc.com>
Signed-off-by: Kent Overstreet <kmo@daterainc.com>

5 files changed, 16 insertions, 8 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index a4c7306ff43d..6d814f463d9e 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -628,6 +628,8 @@ struct cache_set {
         /* Number of moving GC bios in flight */
         struct semaphore        moving_in_flight;
 
+        struct workqueue_struct *moving_gc_wq;
+
         struct btree            *root;
 
 #ifdef CONFIG_BCACHE_DEBUG
diff --git a/drivers/md/bcache/movinggc.c b/drivers/md/bcache/movinggc.c
index 9eb60d102de8..8c7205186d08 100644
--- a/drivers/md/bcache/movinggc.c
+++ b/drivers/md/bcache/movinggc.c
@@ -115,7 +115,7 @@ static void write_moving(struct closure *cl)
                 closure_call(&op->cl, bch_data_insert, NULL, cl);
         }
 
-        continue_at(cl, write_moving_finish, system_wq);
+        continue_at(cl, write_moving_finish, op->wq);
 }
 
 static void read_moving_submit(struct closure *cl)
@@ -125,7 +125,7 @@ static void read_moving_submit(struct closure *cl)
 
         bch_submit_bbio(bio, io->op.c, &io->w->key, 0);
 
-        continue_at(cl, write_moving, system_wq);
+        continue_at(cl, write_moving, io->op.wq);
 }
 
 static void read_moving(struct cache_set *c)
@@ -160,6 +160,7 @@ static void read_moving(struct cache_set *c)
                 io->w           = w;
                 io->op.inode    = KEY_INODE(&w->key);
                 io->op.c        = c;
+                io->op.wq       = c->moving_gc_wq;
 
                 moving_init(io);
                 bio = &io->bio.bio;
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index fc14ba3f6d05..3e880869871f 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -248,7 +248,7 @@ static void bch_data_insert_keys(struct closure *cl)
                 atomic_dec_bug(journal_ref);
 
         if (!op->insert_data_done)
-                continue_at(cl, bch_data_insert_start, bcache_wq);
+                continue_at(cl, bch_data_insert_start, op->wq);
 
         bch_keylist_free(&op->insert_keys);
         closure_return(cl);
@@ -297,7 +297,7 @@ static void bch_data_invalidate(struct closure *cl)
         op->insert_data_done = true;
         bio_put(bio);
 out:
-        continue_at(cl, bch_data_insert_keys, bcache_wq);
+        continue_at(cl, bch_data_insert_keys, op->wq);
 }
 
 static void bch_data_insert_error(struct closure *cl)
@@ -340,7 +340,7 @@ static void bch_data_insert_endio(struct bio *bio, int error)
                 if (op->writeback)
                         op->error = error;
                 else if (!op->replace)
-                        set_closure_fn(cl, bch_data_insert_error, bcache_wq);
+                        set_closure_fn(cl, bch_data_insert_error, op->wq);
                 else
                         set_closure_fn(cl, NULL, NULL);
         }
@@ -376,7 +376,7 @@ static void bch_data_insert_start(struct closure *cl)
                 if (bch_keylist_realloc(&op->insert_keys,
                                         3 + (op->csum ? 1 : 0),
                                         op->c))
-                        continue_at(cl, bch_data_insert_keys, bcache_wq);
+                        continue_at(cl, bch_data_insert_keys, op->wq);
 
                 k = op->insert_keys.top;
                 bkey_init(k);
@@ -413,7 +413,7 @@ static void bch_data_insert_start(struct closure *cl)
         } while (n != bio);
 
         op->insert_data_done = true;
-        continue_at(cl, bch_data_insert_keys, bcache_wq);
+        continue_at(cl, bch_data_insert_keys, op->wq);
 err:
         /* bch_alloc_sectors() blocks if s->writeback = true */
         BUG_ON(op->writeback);
@@ -442,7 +442,7 @@ err:
                 bio_put(bio);
 
                 if (!bch_keylist_empty(&op->insert_keys))
-                        continue_at(cl, bch_data_insert_keys, bcache_wq);
+                        continue_at(cl, bch_data_insert_keys, op->wq);
                 else
                         closure_return(cl);
         }
@@ -824,6 +824,7 @@ static inline struct search *search_alloc(struct bio *bio,
         s->iop.error            = 0;
         s->iop.flags            = 0;
         s->iop.flush_journal    = (bio->bi_rw & (REQ_FLUSH|REQ_FUA)) != 0;
+        s->iop.wq               = bcache_wq;
 
         return s;
 }
diff --git a/drivers/md/bcache/request.h b/drivers/md/bcache/request.h
index 39f21dbedc38..c117c4082aa2 100644
--- a/drivers/md/bcache/request.h
+++ b/drivers/md/bcache/request.h
@@ -7,6 +7,7 @@ struct data_insert_op {
         struct closure          cl;
         struct cache_set        *c;
         struct bio              *bio;
+        struct workqueue_struct *wq;
 
         unsigned                inode;
         uint16_t                write_point;
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index fb343276beef..ddfde380b49f 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1356,6 +1356,8 @@ static void cache_set_free(struct closure *cl)
         bch_bset_sort_state_free(&c->sort);
         free_pages((unsigned long) c->uuids, ilog2(bucket_pages(c)));
 
+        if (c->moving_gc_wq)
+                destroy_workqueue(c->moving_gc_wq);
         if (c->bio_split)
                 bioset_free(c->bio_split);
         if (c->fill_iter)
@@ -1522,6 +1524,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
             !(c->fill_iter = mempool_create_kmalloc_pool(1, iter_size)) ||
             !(c->bio_split = bioset_create(4, offsetof(struct bbio, bio))) ||
             !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) ||
+            !(c->moving_gc_wq = create_workqueue("bcache_gc")) ||
             bch_journal_alloc(c) ||
             bch_btree_cache_alloc(c) ||
             bch_open_buckets_alloc(c) ||