From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (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 10CCF1F4625 for ; Mon, 10 Feb 2025 16:41:09 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739205674; cv=none; b=IYDaYc7oGjxE63DqOjk81QJ3XMKKsxKrHdRxZ6AYClHvlve6kvLqOtKUrdaySNM5RpXZuaQkhaIV8nQEmciqPEFQyBYzoBZQeRfkCjV4TqB4tfpzzkviUibXeDOfYKE/Wr0XvhSIIKyW3jXVoSoWhbqKZHQfri3xUuVIJSgm2ho= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739205674; c=relaxed/simple; bh=rqymZ0NurZ4uwh32hr1IPMHTuWwsGkx6A3GbSMGR6Pg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EWnBG9jxBFOZA8nBz60CVrFt06mitn6plhre2P5wBCRhSJ9hfyY5YorUSl4wA96jTpEao5913z2N7hhu3saVXpX5PLLTlt2H2OS3W+KGDAHEpTz2twYdmemdm+UFZ8un/LzMrJKDEywkOaLDro5fD4qyglXlO9fkodScd34D0i8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=V6guh7cP; arc=none smtp.client-ip=95.215.58.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="V6guh7cP" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1739205668; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PLKGhgf5O0fUKKbSlKGAihHeN6U7qrQ5l3EDkpVZISY=; b=V6guh7cPGDO66uUcdvNqRSqMaULGvA+Qft0V/aGzvtm0qN+vVAro0jceFR2y0A3QPrti+R 4Vkk8U2ufOnStWo84Fv4ONxpbj68tL48y//OSkQEE25rMAlaX/gu2Ym8GzJ/d/F46TTIHQ Nfj5mxf90dLgCQESDZ2yaBJd9PhmEWI= Date: Mon, 10 Feb 2025 08:41:00 -0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v7 5/6] kernfs: Use RCU to access kernfs_node::parent. Content-Language: en-GB To: Sebastian Andrzej Siewior , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Cc: =?UTF-8?Q?Michal_Koutn=C3=BD?= , "Paul E. McKenney" , Boqun Feng , Greg Kroah-Hartman , Hillf Danton , Johannes Weiner , Marco Elver , Tejun Heo , tglx@linutronix.de, Andrii Nakryiko , Eduard Zingerman , Mykola Lysenko , bpf@vger.kernel.org References: <20250203135023.416828-1-bigeasy@linutronix.de> <20250203135023.416828-6-bigeasy@linutronix.de> <20250210084331.IJB3qKdl@linutronix.de> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20250210084331.IJB3qKdl@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2/10/25 12:43 AM, Sebastian Andrzej Siewior wrote: > On 2025-02-03 14:50:22 [+0100], To cgroups@vger.kernel.org wrote: >> kernfs_rename_lock is used to obtain stable kernfs_node::{name|parent} >> pointer. This is a preparation to access kernfs_node::parent under RCU >> and ensure that the pointer remains stable under the RCU lifetime >> guarantees. > … > > The robot complained that the selftests for bpf broke. As it turns out, > the tests access kernfs_node::{parent|name} and after the rename > ::parent is gone so it does not compile. > If there are no objections, I would merge this into 5/6 and repost. > "test_progs -a test_profiler" passes. > > diff --git a/tools/testing/selftests/bpf/progs/profiler.inc.h b/tools/testing/selftests/bpf/progs/profiler.inc.h > index 8bd1ebd7d6afd..a4f518ee5f4de 100644 > --- a/tools/testing/selftests/bpf/progs/profiler.inc.h > +++ b/tools/testing/selftests/bpf/progs/profiler.inc.h > @@ -223,7 +223,7 @@ static INLINE void* read_full_cgroup_path(struct kernfs_node* cgroup_node, > if (bpf_cmp_likely(filepart_length, <=, MAX_PATH)) { > payload += filepart_length; > } > - cgroup_node = BPF_CORE_READ(cgroup_node, parent); > + cgroup_node = BPF_CORE_READ(cgroup_node, __parent); > } > return payload; > } > @@ -300,6 +300,7 @@ static INLINE void* populate_cgroup_info(struct cgroup_data_t* cgroup_data, > cgroup_data->cgroup_proc_length = 0; > cgroup_data->cgroup_full_length = 0; > > + bpf_rcu_read_lock(); > size_t cgroup_root_length = > bpf_probe_read_kernel_str(payload, MAX_PATH, > BPF_CORE_READ(root_kernfs, name)); > @@ -323,6 +324,7 @@ static INLINE void* populate_cgroup_info(struct cgroup_data_t* cgroup_data, > cgroup_data->cgroup_full_length = payload_end_pos - payload; > payload = payload_end_pos; > } > + bpf_rcu_read_unlock(); All programs calling this function populate_cgroup_info() is not sleepable program so the whole prog is protected by rcu and there is no need for above bpf_rcu_read_{lock,unlock}(). > > return (void*)payload; > }