bcachefs: Make sure to drop/retake btree locks before reclaim

We really don't want to be invoking memory reclaim with btree locks
held: even aside from (solvable, but tricky) recursion issues, it can
cause painful to diagnose performance edge cases.

This fixes a recently reported issue in btree_key_can_insert_cached().

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Reported-by: Mateusz Guzik <mjguzik@gmail.com>
Fixes: https://lore.kernel.org/linux-bcachefs/CAGudoHEsb_hGRMeWeXh+UF6po0qQuuq_NKSEo+s1sEb6bDLjpA@mail.gmail.com/T/

diff --git a/fs/bcachefs/btree_trans_commit.c b/fs/bcachefs/btree_trans_commit.c
index 02491f7bb8314428e4a986a8b0d143432137a90e..55a120eb8692b38fdb2fe1f36b0718ff9ed44e9a 100644 (file)
--- a/fs/bcachefs/btree_trans_commit.c
+++ b/fs/bcachefs/btree_trans_commit.c
@@ -368,6 +368,45 @@ static inline int btree_key_can_insert(struct btree_trans *trans,
        return 0;
 }
 
+noinline static int
+btree_key_can_insert_cached_slowpath(struct btree_trans *trans, unsigned flags,
+                                    struct btree_path *path, unsigned new_u64s)
+{
+       struct bch_fs *c = trans->c;
+       struct btree_insert_entry *i;
+       struct bkey_cached *ck = (void *) path->l[0].b;
+       struct bkey_i *new_k;
+       int ret;
+
+       bch2_trans_unlock_write(trans);
+       bch2_trans_unlock(trans);
+
+       new_k = kmalloc(new_u64s * sizeof(u64), GFP_KERNEL);
+       if (!new_k) {
+               bch_err(c, "error allocating memory for key cache key, btree %s u64s %u",
+                       bch2_btree_id_str(path->btree_id), new_u64s);
+               return -BCH_ERR_ENOMEM_btree_key_cache_insert;
+       }
+
+       ret =   bch2_trans_relock(trans) ?:
+               bch2_trans_lock_write(trans);
+       if (unlikely(ret)) {
+               kfree(new_k);
+               return ret;
+       }
+
+       memcpy(new_k, ck->k, ck->u64s * sizeof(u64));
+
+       trans_for_each_update(trans, i)
+               if (i->old_v == &ck->k->v)
+                       i->old_v = &new_k->v;
+
+       kfree(ck->k);
+       ck->u64s        = new_u64s;
+       ck->k           = new_k;
+       return 0;
+}
+
 static int btree_key_can_insert_cached(struct btree_trans *trans, unsigned flags,
                                       struct btree_path *path, unsigned u64s)
 {
@@ -394,12 +433,9 @@ static int btree_key_can_insert_cached(struct btree_trans *trans, unsigned flags
                return 0;
 
        new_u64s        = roundup_pow_of_two(u64s);
-       new_k           = krealloc(ck->k, new_u64s * sizeof(u64), GFP_NOFS);
-       if (!new_k) {
-               bch_err(c, "error allocating memory for key cache key, btree %s u64s %u",
-                       bch2_btree_id_str(path->btree_id), new_u64s);
-               return -BCH_ERR_ENOMEM_btree_key_cache_insert;
-       }
+       new_k           = krealloc(ck->k, new_u64s * sizeof(u64), GFP_NOWAIT);
+       if (unlikely(!new_k))
+               return btree_key_can_insert_cached_slowpath(trans, flags, path, new_u64s);
 
        trans_for_each_update(trans, i)
                if (i->old_v == &ck->k->v)