sock_map: Add a cond_resched() in sock_hash_free()

Several syzbot soft lockup reports all have in common sock_hash_free()

If a map with a large number of buckets is destroyed, we need to yield
the cpu when needed.

Fixes: 75e68e5 ("bpf, sockhash: Synchronize delete from bucket list on map free")
Reported-by: syzbot <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Martin KaFai Lau <[email protected]>
Acked-by: John Fastabend <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: edumazet

net/core/sock_map.c

@@ -1183,6 +1183,7 @@ static void sock_hash_free(struct bpf_map *map)
 			sock_put(elem->sk);
 			sock_hash_free_elem(htab, elem);
 		}
+		cond_resched();
 	}
 
 	/* wait for psock readers accessing its map link */