bcachefs: Always give out journal pre-res if we already have one

This is better than skipping the journal pre-reservation if we already
have one - we should still acount for the journal reservation we're
going to have to get.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_update_interior.c

@@ -864,8 +864,11 @@ bch2_btree_update_start(struct btree_trans *trans, enum btree_id id,
 {
 	struct bch_fs *c = trans->c;
 	struct btree_update *as;
-	int ret, disk_res_flags = (flags & BTREE_INSERT_NOFAIL)
+	int disk_res_flags = (flags & BTREE_INSERT_NOFAIL)
 		? BCH_DISK_RESERVATION_NOFAIL : 0;
+	int journal_flags = (flags & BTREE_INSERT_JOURNAL_RESERVED)
+		? JOURNAL_RES_GET_RECLAIM : 0;
+	int ret = 0;
 
 	/*
 	 * This check isn't necessary for correctness - it's just to potentially
@@ -888,10 +891,9 @@ bch2_btree_update_start(struct btree_trans *trans, enum btree_id id,
 	bch2_keylist_init(&as->new_keys, as->_new_keys);
 	bch2_keylist_init(&as->parent_keys, as->inline_keys);
 
-	if (!(flags & BTREE_INSERT_JOURNAL_RESERVED))
 	ret = bch2_journal_preres_get(&c->journal, &as->journal_preres,
 				      BTREE_UPDATE_JOURNAL_RES,
-					      JOURNAL_RES_GET_NONBLOCK);
+				      journal_flags|JOURNAL_RES_GET_NONBLOCK);
 	if (ret == -EAGAIN) {
 		if (flags & BTREE_INSERT_NOUNLOCK)
 			return ERR_PTR(-EINTR);
@@ -899,7 +901,8 @@ bch2_btree_update_start(struct btree_trans *trans, enum btree_id id,
 		bch2_trans_unlock(trans);
 
 		ret = bch2_journal_preres_get(&c->journal, &as->journal_preres,
-					      BTREE_UPDATE_JOURNAL_RES, 0);
+				BTREE_UPDATE_JOURNAL_RES,
+				journal_flags);
 		if (ret)
 			return ERR_PTR(ret);
 

fs/bcachefs/journal.c

@@ -427,9 +427,10 @@ int bch2_journal_res_get_slowpath(struct journal *j, struct journal_res *res,
 
 static bool journal_preres_available(struct journal *j,
 				     struct journal_preres *res,
-				     unsigned new_u64s)
+				     unsigned new_u64s,
+				     unsigned flags)
 {
-	bool ret = bch2_journal_preres_get_fast(j, res, new_u64s);
+	bool ret = bch2_journal_preres_get_fast(j, res, new_u64s, flags);
 
 	if (!ret)
 		bch2_journal_reclaim_work(&j->reclaim_work.work);
@@ -439,13 +440,14 @@ static bool journal_preres_available(struct journal *j,
 
 int __bch2_journal_preres_get(struct journal *j,
 			      struct journal_preres *res,
-			      unsigned new_u64s)
+			      unsigned new_u64s,
+			      unsigned flags)
 {
 	int ret;
 
 	closure_wait_event(&j->preres_wait,
 		   (ret = bch2_journal_error(j)) ||
-		   journal_preres_available(j, res, new_u64s));
+		   journal_preres_available(j, res, new_u64s, flags));
 	return ret;
 }
 

fs/bcachefs/journal.h

@@ -301,6 +301,7 @@ int bch2_journal_res_get_slowpath(struct journal *, struct journal_res *,
 #define JOURNAL_RES_GET_NONBLOCK	(1 << 0)
 #define JOURNAL_RES_GET_CHECK		(1 << 1)
 #define JOURNAL_RES_GET_RESERVED	(1 << 2)
+#define JOURNAL_RES_GET_RECLAIM		(1 << 3)
 
 static inline int journal_res_get_fast(struct journal *j,
 				       struct journal_res *res,
@@ -408,11 +409,12 @@ static inline void bch2_journal_preres_put(struct journal *j,
 }
 
 int __bch2_journal_preres_get(struct journal *,
-			struct journal_preres *, unsigned);
+			struct journal_preres *, unsigned, unsigned);
 
 static inline int bch2_journal_preres_get_fast(struct journal *j,
 					       struct journal_preres *res,
-					       unsigned new_u64s)
+					       unsigned new_u64s,
+					       unsigned flags)
 {
 	int d = new_u64s - res->u64s;
 	union journal_preres_state old, new;
@@ -423,7 +425,15 @@ static inline int bch2_journal_preres_get_fast(struct journal *j,
 
 		new.reserved += d;
 
-		if (new.reserved > new.remaining)
+		/*
+		 * If we're being called from the journal reclaim path, we have
+		 * to unconditionally give out the pre-reservation, there's
+		 * nothing else sensible we can do - otherwise we'd recurse back
+		 * into the reclaim path and deadlock:
+		 */
+
+		if (!(flags & JOURNAL_RES_GET_RECLAIM) &&
+		    new.reserved > new.remaining)
 			return 0;
 	} while ((v = atomic64_cmpxchg(&j->prereserved.counter,
 				       old.v, new.v)) != old.v);
@@ -440,13 +450,13 @@ static inline int bch2_journal_preres_get(struct journal *j,
 	if (new_u64s <= res->u64s)
 		return 0;
 
-	if (bch2_journal_preres_get_fast(j, res, new_u64s))
+	if (bch2_journal_preres_get_fast(j, res, new_u64s, flags))
 		return 0;
 
 	if (flags & JOURNAL_RES_GET_NONBLOCK)
 		return -EAGAIN;
 
-	return __bch2_journal_preres_get(j, res, new_u64s);
+	return __bch2_journal_preres_get(j, res, new_u64s, flags);
 }
 
 /* journal_entry_res: */