From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A01004A843F; Tue, 15 Sep 2026 15:43:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789487001; cv=none; b=ai/6bfENtAiJL4+TNrJXXKKhgYd/LCOfaEIZTlSBwvlZ313RyIbeXhfBMTHl9u/zXWduPN0ujG2N+46Mh51P+QnaZ4eCVus7yZQIhQFtwif8wk1e/GH6gSvn4o0KGIz3HbqtadYsB+e2bjB/m82GH95kc3lXhUb6FVihz1fqBuc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789487001; c=relaxed/simple; bh=qFCqUbrCnm9nlAl6oCdoOhTHrnAvIZ4v+CZ2YyXqn+A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=i7mA+LRD4KWtXlW0jLkS2s821/XYfgEBpCCT+PjhKungFSegK0lohjV6wYhYaLTJEqjkhGxeDdrvFzUpLhpoZUMM7Hb+a+RuJWpi3g4sBacsLJWt4/eM6FkF59IjLUN5brA0gNM1X0EPBoOjY4UxlTxwYyQHg0K/RXdtNrXmz2k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Vjs8XPsR; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Vjs8XPsR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ED5D51F000FF; Tue, 15 Sep 2026 15:43:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789486999; bh=Ea82/tawItNRe2IFAR6CaVCqB+s+mHaxUmuCD2UwtLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Vjs8XPsRQeyYZO+Ztfb7J/IU3HYbsvw+E2/nmRp7I1IIsp2hj9/O9a5Zuqyi071hM fVHQnHxbmDPnUuKIGw/IjxlsZX/1hnKxPg8k+8lHsMUaW/RTGzQfMNvNlK4ZKYFzbs cuDBAO1ow1xwMmNwHmpz21F6n3YM6gANGCV28MRZtOmouoTdskaYi6va31DXngsJgO md47KBxXcURP465JTZfKr+VlLY3qhio47f8F+LWUuNQhiXXIgeoSR3fUNl1mev7RSl K+bjUExsytbYYsWjaycWKLvdAabnqZF8ifHm3GxS+YbyRtUWGAjgeXsy/UecOLk8cZ fV2P4/1/7mCDw== From: Puranjay Mohan To: bpf@vger.kernel.org, rcu@vger.kernel.org Cc: Puranjay Mohan , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Martin KaFai Lau" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Song Liu" , "Yonghong Song" , "Harry Yoo (Oracle)" , "Paul E. McKenney" Subject: [PATCH bpf-next v4 3/4] bpf: Add bpf_call_rcu_tasks_trace() kfunc Date: Tue, 15 Sep 2026 08:42:46 -0700 Message-ID: <20260915154248.3612028-4-puranjay@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260915154248.3612028-1-puranjay@kernel.org> References: <20260915154248.3612028-1-puranjay@kernel.org> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sleepable BPF programs hold rcu_read_lock_trace(), not rcu_read_lock(), so a plain RCU grace period does not wait for them. A program whose readers are sleepable needs this flavour to defer reclaim safely. call_rcu_tasks_trace() is call_srcu() on rcu_tasks_trace_srcu_struct and SRCU invokes callbacks with BH disabled, so the callback is still not sleepable. It does run from a kworker rather than softirq or the rcuc/rcuo kthread, so a callback must not assume anything about current. Only the queueing call differs, so the two share struct bpf_rcu_head and all of the verifier plumbing. Signed-off-by: Puranjay Mohan --- kernel/bpf/helpers.c | 57 +++++++++++++++++++++++++++++++------------ kernel/bpf/verifier.c | 7 ++++-- 2 files changed, 47 insertions(+), 17 deletions(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 6debb92fc8740..f12c612e36097 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -4710,21 +4710,10 @@ static void bpf_rcu_run_callback(struct rcu_head *rcu) bpf_prog_put(prog); } -/** - * bpf_call_rcu - Invoke a BPF callback after an RCU grace period - * @rh: struct bpf_rcu_head in a BPF map value - * @map__const_map: bpf_map that embeds struct bpf_rcu_head in the values - * @callback: BPF subprogram, invoked as callback(map, key, value) for the value holding @rh - * @aux: bpf_prog_aux of the caller, implicitly set by the verifier - * - * Return: 0, -EBUSY if @rh is already queued, -EPERM if @map is held by neither a process - * nor bpffs, or -EBADF if the calling program is going away. - */ -__bpf_kfunc int bpf_call_rcu(struct bpf_rcu_head *rh, void *map__const_map, - bpf_rcu_callback_t callback, struct bpf_prog_aux *aux) +static int __bpf_call_rcu(struct bpf_rcu_head *rh, struct bpf_map *map, void *callback, + struct bpf_prog_aux *aux, bool trace) { struct bpf_rcu_head_kern *rhk = (void *)rh; - struct bpf_map *map = map__const_map; struct bpf_prog *prog; BUILD_BUG_ON(sizeof(struct bpf_rcu_head_kern) > sizeof(struct bpf_rcu_head)); @@ -4744,13 +4733,50 @@ __bpf_kfunc int bpf_call_rcu(struct bpf_rcu_head *rh, void *map__const_map, return -EBADF; } - rhk->callback_fn = (bpf_callback_t)(void *)callback; + rhk->callback_fn = (bpf_callback_t)callback; rhk->map = map; rhk->prog = prog; - call_rcu(&rhk->rcu, bpf_rcu_run_callback); + if (trace) + call_rcu_tasks_trace(&rhk->rcu, bpf_rcu_run_callback); + else + call_rcu(&rhk->rcu, bpf_rcu_run_callback); return 0; } +/** + * bpf_call_rcu - Invoke a BPF callback after an RCU grace period + * @rh: struct bpf_rcu_head in a BPF map value + * @map__const_map: bpf_map that embeds struct bpf_rcu_head in the values + * @callback: BPF subprogram, invoked as callback(map, key, value) for the value holding @rh + * @aux: bpf_prog_aux of the caller, implicitly set by the verifier + * + * Return: 0, -EBUSY if @rh is already queued, -EPERM if @map is held by neither a process + * nor bpffs, or -EBADF if the calling program is going away. + */ +__bpf_kfunc int bpf_call_rcu(struct bpf_rcu_head *rh, void *map__const_map, + bpf_rcu_callback_t callback, struct bpf_prog_aux *aux) +{ + return __bpf_call_rcu(rh, map__const_map, callback, aux, false); +} + +/** + * bpf_call_rcu_tasks_trace - Invoke a BPF callback after an RCU tasks trace grace period + * @rh: struct bpf_rcu_head in a BPF map value + * @map__const_map: bpf_map that embeds struct bpf_rcu_head in the values + * @callback: BPF subprogram, invoked as callback(map, key, value) for the value holding @rh + * @aux: bpf_prog_aux of the caller, implicitly set by the verifier + * + * Waits for sleepable BPF programs too. The callback itself is not sleepable either way. + * + * Return: 0, -EBUSY if @rh is already queued, -EPERM if @map is held by neither a process + * nor bpffs, or -EBADF if the calling program is going away. + */ +__bpf_kfunc int bpf_call_rcu_tasks_trace(struct bpf_rcu_head *rh, void *map__const_map, + bpf_rcu_callback_t callback, struct bpf_prog_aux *aux) +{ + return __bpf_call_rcu(rh, map__const_map, callback, aux, true); +} + static int make_file_dynptr(struct file *file, u32 flags, bool may_sleep, struct bpf_dynptr_kern *ptr) { @@ -5045,6 +5071,7 @@ BTF_ID_FLAGS(func, bpf_stream_print_stack, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE) BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_call_rcu, KF_IMPLICIT_ARGS) +BTF_ID_FLAGS(func, bpf_call_rcu_tasks_trace, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_dynptr_from_file) BTF_ID_FLAGS(func, bpf_dynptr_file_discard, KF_RELEASE) BTF_ID_FLAGS(func, bpf_timer_cancel_async) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7051e19bb78b3..33d25b0e488eb 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -572,7 +572,7 @@ static bool is_async_cb_sleepable(struct bpf_verifier_env *env, struct bpf_insn if (bpf_helper_call(insn) && insn->imm == BPF_FUNC_timer_set_callback) return false; - /* bpf_call_rcu callbacks are never sleepable. */ + /* bpf_call_rcu and bpf_call_rcu_tasks_trace callbacks are never sleepable. */ if (bpf_pseudo_kfunc_call(insn) && insn->off == 0 && is_call_rcu_kfunc(insn->imm)) return false; @@ -12584,6 +12584,7 @@ enum special_kfunc_type { KF_bpf_task_work_schedule_signal, KF_bpf_task_work_schedule_resume, KF_bpf_call_rcu, + KF_bpf_call_rcu_tasks_trace, KF_bpf_arena_alloc_pages, KF_bpf_arena_free_pages, KF_bpf_arena_reserve_pages, @@ -12678,6 +12679,7 @@ BTF_ID(func, __bpf_trap) BTF_ID(func, bpf_task_work_schedule_signal) BTF_ID(func, bpf_task_work_schedule_resume) BTF_ID(func, bpf_call_rcu) +BTF_ID(func, bpf_call_rcu_tasks_trace) BTF_ID(func, bpf_arena_alloc_pages) BTF_ID(func, bpf_arena_free_pages) BTF_ID(func, bpf_arena_reserve_pages) @@ -12751,7 +12753,8 @@ static bool is_bpf_rbtree_add_kfunc(u32 func_id) static bool is_call_rcu_kfunc(u32 func_id) { - return func_id == special_kfunc_list[KF_bpf_call_rcu]; + return func_id == special_kfunc_list[KF_bpf_call_rcu] || + func_id == special_kfunc_list[KF_bpf_call_rcu_tasks_trace]; } static bool is_task_work_add_kfunc(u32 func_id) -- 2.53.0-Meta