From patchwork Thu Aug 3 10:09:32 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 130499 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:9f41:0:b0:3e4:2afc:c1 with SMTP id v1csp1085419vqx; Thu, 3 Aug 2023 04:40:13 -0700 (PDT) X-Google-Smtp-Source: APBJJlE9IBcPhgXDCraZPXKz//RMiyHq0jdWGKIChF0FrdrZPs8XzVch9PJzRyKw39SxxoTocZKw X-Received: by 2002:a9d:7ad1:0:b0:6b9:304a:e778 with SMTP id m17-20020a9d7ad1000000b006b9304ae778mr17500331otn.34.1691062813629; Thu, 03 Aug 2023 04:40:13 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1691062813; cv=none; d=google.com; s=arc-20160816; b=Q53R2amtYx5ptmRtiYPzV8pchvr30duyvvt9hCmT/RGT5ZWNLNSA9E1c5cUA76/DRT 4hPhkeQJa937oe5KnZSvVdeFsdZ2kJE/qMxqBn1wJfA6iLnX4YZ5CosF+nwViMsPkfiJ LW8wJ8a90zATeV/slSUKMAiY0CEE5XPr+RcNkaUzoPrpo97FRmp4tpEmhE+Al3zaluVD gIok2gb4P/+EA5k7yWxfHkgeRS5VFVdN741mc2DZx6VvCkzYq5BX4c2yuDiR5VJuTs4g tVFUbEuSbEHOJRH6/KspTbLlC2xU0d92VUwUb2L0336yjYcVeFYDjnGVgeZlcII6xUaH dRFQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:dkim-signature :dkim-signature:from; bh=Ad7l9FuC31NWow/lJV/fHJBllejOmCcZbpiHniM7Z+Q=; fh=XmTwOPuyyn2SXWnZqO4WlLJ8UucNQ7smOIqArV3zDe4=; b=A4hOpJc/KWReskKhPMOsxFap/gb0+KceT1bVktqc1/auP5zZ1ux6DsS9pKbXde4ajV wLyWJjSM87poZ4OG57SvTNvYL/vEKU4PvJqWn+XGYl10LcSn13BfxbreMVWVnXcn+i4u bEqPE+X4oNH3WGlVKk90KqgAMgJ6mdbAt/dAXLVjMnJN/db5e66TlkAvjgy/Vq+L518M bVowQh+Z7DgjerMXV02FeCzHlrfT6GKoeCyVFPUI4QQ6i/azO2kU/CJcTnaVCGZGc87S gtyZkyoVn0pr4btrZWSMyBwQSdWc8NmN+Y5qZy/TYpBONIZHwAQTDrwre1xg78GZm0e7 8w1w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b="0z/+vymv"; dkim=neutral (no key) header.i=@linutronix.de; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id d12-20020a63f24c000000b00563da4d2a77si262277pgk.867.2023.08.03.04.39.59; Thu, 03 Aug 2023 04:40:13 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b="0z/+vymv"; dkim=neutral (no key) header.i=@linutronix.de; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235137AbjHCKJr (ORCPT + 99 others); Thu, 3 Aug 2023 06:09:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49390 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235104AbjHCKJn (ORCPT ); Thu, 3 Aug 2023 06:09:43 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D562630C7 for ; Thu, 3 Aug 2023 03:09:40 -0700 (PDT) From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1691057379; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ad7l9FuC31NWow/lJV/fHJBllejOmCcZbpiHniM7Z+Q=; b=0z/+vymvQCLuGHrgEYbwn4yxHyfod2bOGtQNIik0z+Le1Jb6oZOG210FzMcArEg3KDT/Hq /D97/1T4nvj7BV2nfReSEqchmhgf0MRz+/77xdXepfuSOI29b1LMOMdArFOtqLymFMJtzy GV/mPb5L50mF3rX8PZ2w0foqX8RRH2I5sK8E9PHSIgKadIhn3T+uivAe+/lDx6Sw8R+DfK 4M6PagdTPuyNfKJmq0pCHg3zOc5amUHebL1+K8OMt8bLYulzLNvcP2oEJobKv6R72T/Eqf kAbYn7dY7NGtNth4NpKBV+AnLhs3u7qteXhcj6vdcCObwk7u+YYTWbBBHD+mnQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1691057379; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ad7l9FuC31NWow/lJV/fHJBllejOmCcZbpiHniM7Z+Q=; b=Bq1865ba57I5cPKPyN55oWdYTG93v10BQXqtmYoFHViLrOqeBuNC/n90qZcI40QN0Q8EnW mc2ddc5kT/Z5p5Cw== To: linux-kernel@vger.kernel.org Cc: "Eric W. Biederman" , Oleg Nesterov , Peter Zijlstra , Thomas Gleixner , Sebastian Andrzej Siewior Subject: [PATCH 2/2] signal: Don't disable preemption in ptrace_stop() on PREEMPT_RT. Date: Thu, 3 Aug 2023 12:09:32 +0200 Message-Id: <20230803100932.325870-3-bigeasy@linutronix.de> In-Reply-To: <20230803100932.325870-1-bigeasy@linutronix.de> References: <20230803100932.325870-1-bigeasy@linutronix.de> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1773207880893492865 X-GMAIL-MSGID: 1773207880893492865 On PREEMPT_RT keeping preemption disabled during the invocation of cgroup_enter_frozen() is a problem because the function acquires css_set_lock which is a sleeping lock on PREEMPT_RT and must not be acquired with disabled preemption. The preempt-disabled section is only for performance optimisation reasons and can be avoided. Extend the comment and don't disable preemption before scheduling on PREEMPT_RT. Acked-by: Oleg Nesterov Signed-off-by: Sebastian Andrzej Siewior --- kernel/signal.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2333,11 +2333,20 @@ static int ptrace_stop(int exit_code, in * The preempt-disable section ensures that there will be no preemption * between unlock and schedule() and so improving the performance since * the ptracer has no reason to sleep. + * + * On PREEMPT_RT locking tasklist_lock does not disable preemption. + * Therefore the task can be preempted (after + * do_notify_parent_cldstop()) before unlocking tasklist_lock so there + * is no benefit in doing this. The optimisation is harmful on + * PEEMPT_RT because the spinlock_t (in cgroup_enter_frozen()) must not + * be acquired with disabled preemption. */ - preempt_disable(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); read_unlock(&tasklist_lock); cgroup_enter_frozen(); - preempt_enable_no_resched(); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable_no_resched(); schedule(); cgroup_leave_frozen(true);