bpf: replace bpf_timer_init with a generic helper

No code change except for the new flags argument being stored in the
local data struct.
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-2-6c986a5a741f@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -1111,7 +1111,10 @@ struct bpf_hrtimer {
 
 /* the actual struct hidden inside uapi struct bpf_timer */
 struct bpf_async_kern {
-	struct bpf_hrtimer *timer;
+	union {
+		struct bpf_async_cb *cb;
+		struct bpf_hrtimer *timer;
+	};
 	/* bpf_spin_lock is used here instead of spinlock_t to make
 	 * sure that it always fits into space reserved by struct bpf_timer
 	 * regardless of LOCKDEP and spinlock debug flags.
@@ -1119,6 +1122,10 @@ struct bpf_async_kern {
 	struct bpf_spin_lock lock;
 } __attribute__((aligned(8)));
 
+enum bpf_async_type {
+	BPF_ASYNC_TYPE_TIMER = 0,
+};
+
 static DEFINE_PER_CPU(struct bpf_hrtimer *, hrtimer_running);
 
 static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
@@ -1160,46 +1167,55 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer)
 	return HRTIMER_NORESTART;
 }
 
-BPF_CALL_3(bpf_timer_init, struct bpf_async_kern *, timer, struct bpf_map *, map,
-	   u64, flags)
+static int __bpf_async_init(struct bpf_async_kern *async, struct bpf_map *map, u64 flags,
+			    enum bpf_async_type type)
 {
-	clockid_t clockid = flags & (MAX_CLOCKS - 1);
+	struct bpf_async_cb *cb;
 	struct bpf_hrtimer *t;
+	clockid_t clockid;
+	size_t size;
 	int ret = 0;
 
-	BUILD_BUG_ON(MAX_CLOCKS != 16);
-	BUILD_BUG_ON(sizeof(struct bpf_async_kern) > sizeof(struct bpf_timer));
-	BUILD_BUG_ON(__alignof__(struct bpf_async_kern) != __alignof__(struct bpf_timer));
-
 	if (in_nmi())
 		return -EOPNOTSUPP;
 
-	if (flags >= MAX_CLOCKS ||
-	    /* similar to timerfd except _ALARM variants are not supported */
-	    (clockid != CLOCK_MONOTONIC &&
-	     clockid != CLOCK_REALTIME &&
-	     clockid != CLOCK_BOOTTIME))
+	switch (type) {
+	case BPF_ASYNC_TYPE_TIMER:
+		size = sizeof(struct bpf_hrtimer);
+		break;
+	default:
 		return -EINVAL;
-	__bpf_spin_lock_irqsave(&timer->lock);
-	t = timer->timer;
+	}
+
+	__bpf_spin_lock_irqsave(&async->lock);
+	t = async->timer;
 	if (t) {
 		ret = -EBUSY;
 		goto out;
 	}
+
 	/* allocate hrtimer via map_kmalloc to use memcg accounting */
-	t = bpf_map_kmalloc_node(map, sizeof(*t), GFP_ATOMIC, map->numa_node);
-	if (!t) {
+	cb = bpf_map_kmalloc_node(map, size, GFP_ATOMIC, map->numa_node);
+	if (!cb) {
 		ret = -ENOMEM;
 		goto out;
 	}
-	t->cb.value = (void *)timer - map->record->timer_off;
-	t->cb.map = map;
-	t->cb.prog = NULL;
-	rcu_assign_pointer(t->cb.callback_fn, NULL);
-	hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT);
-	t->timer.function = bpf_timer_cb;
-	WRITE_ONCE(timer->timer, t);
-	/* Guarantee the order between timer->timer and map->usercnt. So
+
+	if (type == BPF_ASYNC_TYPE_TIMER) {
+		clockid = flags & (MAX_CLOCKS - 1);
+		t = (struct bpf_hrtimer *)cb;
+
+		hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT);
+		t->timer.function = bpf_timer_cb;
+		cb->value = (void *)async - map->record->timer_off;
+	}
+	cb->map = map;
+	cb->prog = NULL;
+	cb->flags = flags;
+	rcu_assign_pointer(cb->callback_fn, NULL);
+
+	WRITE_ONCE(async->cb, cb);
+	/* Guarantee the order between async->cb and map->usercnt. So
 	 * when there are concurrent uref release and bpf timer init, either
 	 * bpf_timer_cancel_and_free() called by uref release reads a no-NULL
 	 * timer or atomic64_read() below returns a zero usercnt.
@@ -1209,15 +1225,34 @@ BPF_CALL_3(bpf_timer_init, struct bpf_async_kern *, timer, struct bpf_map *, map
 		/* maps with timers must be either held by user space
 		 * or pinned in bpffs.
 		 */
-		WRITE_ONCE(timer->timer, NULL);
-		kfree(t);
+		WRITE_ONCE(async->cb, NULL);
+		kfree(cb);
 		ret = -EPERM;
 	}
 out:
-	__bpf_spin_unlock_irqrestore(&timer->lock);
+	__bpf_spin_unlock_irqrestore(&async->lock);
 	return ret;
 }
 
+BPF_CALL_3(bpf_timer_init, struct bpf_async_kern *, timer, struct bpf_map *, map,
+	   u64, flags)
+{
+	clock_t clockid = flags & (MAX_CLOCKS - 1);
+
+	BUILD_BUG_ON(MAX_CLOCKS != 16);
+	BUILD_BUG_ON(sizeof(struct bpf_async_kern) > sizeof(struct bpf_timer));
+	BUILD_BUG_ON(__alignof__(struct bpf_async_kern) != __alignof__(struct bpf_timer));
+
+	if (flags >= MAX_CLOCKS ||
+	    /* similar to timerfd except _ALARM variants are not supported */
+	    (clockid != CLOCK_MONOTONIC &&
+	     clockid != CLOCK_REALTIME &&
+	     clockid != CLOCK_BOOTTIME))
+		return -EINVAL;
+
+	return __bpf_async_init(timer, map, flags, BPF_ASYNC_TYPE_TIMER);
+}
+
 static const struct bpf_func_proto bpf_timer_init_proto = {
 	.func		= bpf_timer_init,
 	.gpl_only	= true,