bcachefs: More assertions for nocow locking

- assert in shutdown path that no nocow locks are held
 - check for overflow when taking nocow locks

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/nocow_locking.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "bkey_methods.h"
 #include "nocow_locking.h"
 #include "util.h"
 
@@ -29,9 +30,10 @@ void bch2_bucket_nocow_unlock(struct bucket_nocow_lock_table *t, struct bpos buc
 
 	for (i = 0; i < ARRAY_SIZE(l->b); i++)
 		if (l->b[i] == dev_bucket) {
-			BUG_ON(sign(atomic_read(&l->l[i])) != lock_val);
+			int v = atomic_sub_return(lock_val, &l->l[i]);
 
-			if (!atomic_sub_return(lock_val, &l->l[i]))
+			BUG_ON(v && sign(v) != lock_val);
+			if (!v)
 				closure_wake_up(&l->wait);
 			return;
 		}
@@ -64,6 +66,11 @@ got_entry:
 	if (lock_val > 0 ? v < 0 : v > 0)
 		goto fail;
 take_lock:
+	v = atomic_read(&l->l[i]);
+	/* Overflow? */
+	if (v && sign(v + lock_val) != sign(v))
+		goto fail;
+
 	atomic_add(lock_val, &l->l[i]);
 	spin_unlock(&l->lock);
 	return true;
@@ -83,6 +90,7 @@ void __bch2_bucket_nocow_lock(struct bucket_nocow_lock_table *t,
 }
 
 void bch2_nocow_locks_to_text(struct printbuf *out, struct bucket_nocow_lock_table *t)
+
 {
 	unsigned i, nr_zero = 0;
 	struct nocow_lock_bucket *l;
@@ -102,9 +110,13 @@ void bch2_nocow_locks_to_text(struct printbuf *out, struct bucket_nocow_lock_tab
 			prt_printf(out, "(%u empty entries)\n", nr_zero);
 		nr_zero = 0;
 
-		for (i = 0; i < ARRAY_SIZE(l->l); i++)
-			if (atomic_read(&l->l[i]))
-				prt_printf(out, "%llu: %i ", l->b[i], atomic_read(&l->l[i]));
+		for (i = 0; i < ARRAY_SIZE(l->l); i++) {
+			int v = atomic_read(&l->l[i]);
+			if (v) {
+				bch2_bpos_to_text(out, u64_to_bucket(l->b[i]));
+				prt_printf(out, ": %s %u ", v < 0 ? "copy" : "update", abs(v));
+			}
+		}
 		prt_newline(out);
 	}
 
@@ -112,12 +124,21 @@ void bch2_nocow_locks_to_text(struct printbuf *out, struct bucket_nocow_lock_tab
 		prt_printf(out, "(%u empty entries)\n", nr_zero);
 }
 
+void bch2_fs_nocow_locking_exit(struct bch_fs *c)
+{
+	struct bucket_nocow_lock_table *t = &c->nocow_locks;
+
+	for (struct nocow_lock_bucket *l = t->l; l < t->l + ARRAY_SIZE(t->l); l++)
+		for (unsigned j = 0; j < ARRAY_SIZE(l->l); j++)
+			BUG_ON(atomic_read(&l->l[j]));
+}
+
 int bch2_fs_nocow_locking_init(struct bch_fs *c)
 {
-	unsigned i;
+	struct bucket_nocow_lock_table *t = &c->nocow_locks;
 
-	for (i = 0; i < ARRAY_SIZE(c->nocow_locks.l); i++)
-		spin_lock_init(&c->nocow_locks.l[i].lock);
+	for (struct nocow_lock_bucket *l = t->l; l < t->l + ARRAY_SIZE(t->l); l++)
+		spin_lock_init(&l->lock);
 
 	return 0;
 }

fs/bcachefs/nocow_locking.h

@@ -44,6 +44,7 @@ static inline bool bch2_bucket_nocow_trylock(struct bucket_nocow_lock_table *t,
 
 void bch2_nocow_locks_to_text(struct printbuf *, struct bucket_nocow_lock_table *);
 
+void bch2_fs_nocow_locking_exit(struct bch_fs *);
 int bch2_fs_nocow_locking_init(struct bch_fs *);
 
 #endif /* _BCACHEFS_NOCOW_LOCKING_H */

fs/bcachefs/super.c

@@ -484,6 +484,7 @@ static void __bch2_fs_free(struct bch_fs *c)
 	bch2_fs_fsio_exit(c);
 	bch2_fs_ec_exit(c);
 	bch2_fs_encryption_exit(c);
+	bch2_fs_nocow_locking_exit(c);
 	bch2_fs_io_write_exit(c);
 	bch2_fs_io_read_exit(c);
 	bch2_fs_buckets_waiting_for_journal_exit(c);