From patchwork Wed Feb 21 16:25:20 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Tissoires X-Patchwork-Id: 13565934 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 44CEF81AB3; Wed, 21 Feb 2024 16:25:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708532742; cv=none; b=TZlESJiQS17q4CqWphqNT1A8CJ8vk4Lp7ssmj8KEj+7MZbdeux5cj9W+94hNjO7Fv2fiXUAlM+bOCz/O9EG86dnhxW8hVfIgMEnCQdgVFh4q2lCtzkvxeokt+pBOEXa/mazvrowitEVErV4L1e8iQK9cfjcJRpXIpFzwhGPDARo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708532742; c=relaxed/simple; bh=ZYNT6AaQhkuGvT8Z9dQUoI41EykqVHPK+5CqRnyQs3A=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=mUm7JDUMx+5T+A+orbYjhug/xNh54d6zUcQr2uri3pi1+0jskGb7rbb/XYZoxlwuP1mRGP/3bW7CvLoWNCKxm401jOgUkqslHC6fUvycPgMEXMZ6U0EQGp8w1O7cc0Fsku1ZCPyNdOntzXcSz3ye5zWg2y50tGyM6CRV4Qmmb2I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m2iBXTEW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="m2iBXTEW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE27EC433B2; Wed, 21 Feb 2024 16:25:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1708532741; bh=ZYNT6AaQhkuGvT8Z9dQUoI41EykqVHPK+5CqRnyQs3A=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=m2iBXTEWXgULxh3hvLUrKiSzHgnKmHSkFNNoAVbtLUy+WhGa3JBGLTRuKCYOUiLa0 3lyIlTI3YmfYd96dg6z3iHx35L7ZwgYPkqIdBPLqgWl39A8SRKupmQZ4CteLYppLyp rUvitXx4/Zh2Io8PPd/8AXkk93J6mCHdmDwmYerxAKtEh5r+R82u5LjBJc9wzsIvRQ tyhtvKu3lx5dka/z7gZZVQb0FuEcEEp+NGZn/N8NlQk6h4AXZkdjlBAZhpCJP4v3w4 kWxO4WYE2rqA72mC4S7QBDy5XNtCEGZyBNeBzkOPJmH/2d3Vabotg6cip4x66VlL7c 2jw6dkrAyHOzA== From: Benjamin Tissoires Date: Wed, 21 Feb 2024 17:25:20 +0100 Subject: [PATCH RFC bpf-next v3 04/16] bpf/helpers: introduce sleepable bpf_timers Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240221-hid-bpf-sleepable-v3-4-1fb378ca6301@kernel.org> References: <20240221-hid-bpf-sleepable-v3-0-1fb378ca6301@kernel.org> In-Reply-To: <20240221-hid-bpf-sleepable-v3-0-1fb378ca6301@kernel.org> To: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Jiri Kosina , Benjamin Tissoires , Jonathan Corbet , Shuah Khan Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-input@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Benjamin Tissoires X-Mailer: b4 0.12.4 X-Developer-Signature: v=1; a=ed25519-sha256; t=1708532719; l=7906; i=bentiss@kernel.org; s=20230215; h=from:subject:message-id; bh=ZYNT6AaQhkuGvT8Z9dQUoI41EykqVHPK+5CqRnyQs3A=; b=NhATyVXLBVmiUhI3zNu7Frdb/5dMuW4X4D3dXM/NaBaAy0JRXEJNO0fjK1D7kD/h0+fckzBvg 7iaiB1bNfDqDlBCwS7fo235/Sn9HYXfGYGh3WXOQ3gRFFBRjXGYA+yy X-Developer-Key: i=bentiss@kernel.org; a=ed25519; pk=7D1DyAVh6ajCkuUTudt/chMuXWIJHlv2qCsRkIizvFw= They are implemented as a workqueue, which means that there are no guarantees of timing nor ordering. Signed-off-by: Benjamin Tissoires --- changes in v3: - extracted the implementation in bpf_timer only, without bpf_timer_set_sleepable_cb() - rely on schedule_work() only, from bpf_timer_start() - add semaphore to ensure bpf_timer_work_cb() is accessing consistent data changes in v2 (compared to the one attaches to v1 0/9): - make use of a kfunc - add a (non-used) BPF_F_TIMER_SLEEPABLE - the callback is *not* called, it makes the kernel crashes --- include/uapi/linux/bpf.h | 4 +++ kernel/bpf/helpers.c | 92 ++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 82 insertions(+), 14 deletions(-) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index d96708380e52..1fc7ecbd9d33 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -7421,10 +7421,14 @@ struct bpf_core_relo { * - BPF_F_TIMER_ABS: Timeout passed is absolute time, by default it is * relative to current time. * - BPF_F_TIMER_CPU_PIN: Timer will be pinned to the CPU of the caller. + * - BPF_F_TIMER_SLEEPABLE: Timer will run in a sleepable context, with + * no guarantees of ordering nor timing (consider this as being just + * offloaded immediately). */ enum { BPF_F_TIMER_ABS = (1ULL << 0), BPF_F_TIMER_CPU_PIN = (1ULL << 1), + BPF_F_TIMER_SLEEPABLE = (1ULL << 2), }; /* BPF numbers iterator state */ diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 93edf730d288..f9add0abe40a 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -23,6 +23,7 @@ #include #include #include +#include #include "../../lib/kstrtox.h" @@ -1094,13 +1095,19 @@ const struct bpf_func_proto bpf_snprintf_proto = { * bpf_timer_cancel() cancels the timer and decrements prog's refcnt. * Inner maps can contain bpf timers as well. ops->map_release_uref is * freeing the timers when inner map is replaced or deleted by user space. + * + * sleepable_lock protects only the setup of the workqueue, not the callback + * itself. This is done to ensure we don't run concurrently a free of the + * callback or the associated program. */ struct bpf_hrtimer { struct hrtimer timer; + struct work_struct work; struct bpf_map *map; struct bpf_prog *prog; void __rcu *callback_fn; void *value; + struct semaphore sleepable_lock; }; /* the actual struct hidden inside uapi struct bpf_timer */ @@ -1113,6 +1120,55 @@ struct bpf_timer_kern { struct bpf_spin_lock lock; } __attribute__((aligned(8))); +static u32 __bpf_timer_compute_key(struct bpf_hrtimer *timer) +{ + struct bpf_map *map = timer->map; + void *value = timer->value; + + if (map->map_type == BPF_MAP_TYPE_ARRAY) { + struct bpf_array *array = container_of(map, struct bpf_array, map); + + /* compute the key */ + return ((char *)value - array->value) / array->elem_size; + } + + /* hash or lru */ + return *(u32 *)(value - round_up(map->key_size, 8)); +} + +static void bpf_timer_work_cb(struct work_struct *work) +{ + struct bpf_hrtimer *t = container_of(work, struct bpf_hrtimer, work); + struct bpf_map *map = t->map; + void *value = t->value; + bpf_callback_t callback_fn; + u32 key; + + BTF_TYPE_EMIT(struct bpf_timer); + + down(&t->sleepable_lock); + + callback_fn = READ_ONCE(t->callback_fn); + if (!callback_fn) { + up(&t->sleepable_lock); + return; + } + + key = __bpf_timer_compute_key(t); + + /* prevent the callback to be freed by bpf_timer_cancel() while running + * so we can release the semaphore + */ + bpf_prog_inc(t->prog); + + up(&t->sleepable_lock); + + callback_fn((u64)(long)map, (u64)(long)&key, (u64)(long)value, 0, 0); + /* The verifier checked that return value is zero. */ + + bpf_prog_put(t->prog); +} + static DEFINE_PER_CPU(struct bpf_hrtimer *, hrtimer_running); static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) @@ -1121,8 +1177,7 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) struct bpf_map *map = t->map; void *value = t->value; bpf_callback_t callback_fn; - void *key; - u32 idx; + u32 key; BTF_TYPE_EMIT(struct bpf_timer); callback_fn = rcu_dereference_check(t->callback_fn, rcu_read_lock_bh_held()); @@ -1136,17 +1191,9 @@ static enum hrtimer_restart bpf_timer_cb(struct hrtimer *hrtimer) * bpf_map_delete_elem() on the same timer. */ this_cpu_write(hrtimer_running, t); - if (map->map_type == BPF_MAP_TYPE_ARRAY) { - struct bpf_array *array = container_of(map, struct bpf_array, map); - - /* compute the key */ - idx = ((char *)value - array->value) / array->elem_size; - key = &idx; - } else { /* hash or lru */ - key = value - round_up(map->key_size, 8); - } + key = __bpf_timer_compute_key(t); - callback_fn((u64)(long)map, (u64)(long)key, (u64)(long)value, 0, 0); + callback_fn((u64)(long)map, (u64)(long)&key, (u64)(long)value, 0, 0); /* The verifier checked that return value is zero. */ this_cpu_write(hrtimer_running, NULL); @@ -1191,6 +1238,8 @@ BPF_CALL_3(bpf_timer_init, struct bpf_timer_kern *, timer, struct bpf_map *, map t->prog = NULL; rcu_assign_pointer(t->callback_fn, NULL); hrtimer_init(&t->timer, clockid, HRTIMER_MODE_REL_SOFT); + INIT_WORK(&t->work, bpf_timer_work_cb); + sema_init(&t->sleepable_lock, 1); t->timer.function = bpf_timer_cb; WRITE_ONCE(timer->timer, t); /* Guarantee the order between timer->timer and map->usercnt. So @@ -1245,6 +1294,7 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb ret = -EPERM; goto out; } + down(&t->sleepable_lock); prev = t->prog; if (prev != prog) { /* Bump prog refcnt once. Every bpf_timer_set_callback() @@ -1261,6 +1311,7 @@ BPF_CALL_3(bpf_timer_set_callback, struct bpf_timer_kern *, timer, void *, callb t->prog = prog; } rcu_assign_pointer(t->callback_fn, callback_fn); + up(&t->sleepable_lock); out: __bpf_spin_unlock_irqrestore(&timer->lock); return ret; @@ -1282,7 +1333,7 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla if (in_nmi()) return -EOPNOTSUPP; - if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN)) + if (flags & ~(BPF_F_TIMER_ABS | BPF_F_TIMER_CPU_PIN | BPF_F_TIMER_SLEEPABLE)) return -EINVAL; __bpf_spin_lock_irqsave(&timer->lock); t = timer->timer; @@ -1299,7 +1350,10 @@ BPF_CALL_3(bpf_timer_start, struct bpf_timer_kern *, timer, u64, nsecs, u64, fla if (flags & BPF_F_TIMER_CPU_PIN) mode |= HRTIMER_MODE_PINNED; - hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode); + if (flags & BPF_F_TIMER_SLEEPABLE) + schedule_work(&t->work); + else + hrtimer_start(&t->timer, ns_to_ktime(nsecs), mode); out: __bpf_spin_unlock_irqrestore(&timer->lock); return ret; @@ -1346,13 +1400,21 @@ BPF_CALL_1(bpf_timer_cancel, struct bpf_timer_kern *, timer) ret = -EDEADLK; goto out; } + down(&t->sleepable_lock); drop_prog_refcnt(t); + up(&t->sleepable_lock); out: __bpf_spin_unlock_irqrestore(&timer->lock); /* Cancel the timer and wait for associated callback to finish * if it was running. */ ret = ret ?: hrtimer_cancel(&t->timer); + + /* also cancel the sleepable work, but *do not* wait for + * it to finish if it was running as we might not be in a + * sleepable context + */ + ret = ret ?: cancel_work(&t->work); return ret; } @@ -1407,6 +1469,8 @@ void bpf_timer_cancel_and_free(void *val) */ if (this_cpu_read(hrtimer_running) != t) hrtimer_cancel(&t->timer); + + cancel_work_sync(&t->work); kfree(t); }