From patchwork Thu Jul 18 05:43:58 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Masami Hiramatsu (Google)" X-Patchwork-Id: 11048511 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 3346A13A4 for ; Thu, 18 Jul 2019 05:44:39 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 20809287AA for ; Thu, 18 Jul 2019 05:44:39 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 10FFD287AE; Thu, 18 Jul 2019 05:44:39 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id AF499287AA for ; Thu, 18 Jul 2019 05:44:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Vyx/OhRVurpjvnk4AMIoLFn4nSABIuEdAyTEGat2XpE=; b=bXlzohUusGhwLK IqX9qe8qOEgqrkfuoN/kikFz+JuxmH8pr7WrvVmUrqGjknLsL3Zgpq8aQsMi/pxnVHmAOMCpjUTM+ 4WD+PA5OizEmwQv4fkkfv+UKpeh8ZTfGYwiYR5qh9B4eI3meWHVqhlf1LsCQzjKpYtKLOCDjW22HT YyyWhbWEV8AJI49Y2dd7GM0Cja7QFljnLlk0CFAa5hqC4429c12OT79mZecHgwWw6Evc0U4B5aaQS gqH3IRSRowezAInu2CnjreJWLsljExshsiaY6MgRBZCy/ckwOCqoAr1A7/eHRoVPAaBJqyAEk5yWo YIFJESbkTz1T3ldC9gKQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hnzDU-0007nj-G4; Thu, 18 Jul 2019 05:44:32 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hnzCz-0007PY-FW for linux-arm-kernel@lists.infradead.org; Thu, 18 Jul 2019 05:44:03 +0000 Received: from localhost.localdomain (115.42.148.210.bf.2iij.net [210.148.42.115]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BB1742077C; Thu, 18 Jul 2019 05:43:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563428641; bh=gfhHae/Itpt4cAnEUBWjU+vv/jZ4knj9Gh5tlJZH32w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NbZK2rcN4p4Do4xNZrSCrpocqmzJSvw185NluBokppvstd5PDELeRoeBvlxWmbx/j 5Z86mXbG9w36rFsAnbjFo6pNCtSmcdmZCEl3JBF6w4BplF9d9OaxK4npYS1TQtZzq+ o6puJrBaLviuSqMUn4YcVdYNnFDnm7ukvjVfqNoU= From: Masami Hiramatsu To: Catalin Marinas , Will Deacon Subject: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Date: Thu, 18 Jul 2019 14:43:58 +0900 Message-Id: <156342863822.8565.7624877983728871995.stgit@devnote2> X-Mailer: git-send-email 2.20.1 In-Reply-To: <156342860634.8565.14804606041960884732.stgit@devnote2> References: <156342860634.8565.14804606041960884732.stgit@devnote2> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190717_224401_670394_CBB85CC5 X-CRM114-Status: GOOD ( 11.44 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dan Rue , Daniel Diaz , Anders Roxell , Naresh Kamboju , linux-kernel@vger.kernel.org, Matt Hart , "Paul E . McKenney" , linux-arm-kernel@lists.infradead.org, mhiramat@kernel.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Remove rcu_read_lock()/rcu_read_unlock() from debug exception handlers since the software breakpoint can be hit on idle task. Actually, we don't need it because those handlers run in exception context where the interrupts are disabled. This means those are never preempted. Reported-by: Naresh Kamboju Cc: Paul E. McKenney Signed-off-by: Masami Hiramatsu --- arch/arm64/kernel/debug-monitors.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index f8719bd30850..48222a4760c2 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -207,16 +207,16 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr) list = user_mode(regs) ? &user_step_hook : &kernel_step_hook; - rcu_read_lock(); - + /* + * Since single-step exception disables interrupt, this function is + * entirely not preemptible, and we can use rcu list safely here. + */ list_for_each_entry_rcu(hook, list, node) { retval = hook->fn(regs, esr); if (retval == DBG_HOOK_HANDLED) break; } - rcu_read_unlock(); - return retval; } NOKPROBE_SYMBOL(call_step_hook); @@ -305,14 +305,16 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) list = user_mode(regs) ? &user_break_hook : &kernel_break_hook; - rcu_read_lock(); + /* + * Since brk exception disables interrupt, this function is + * entirely not preemptible, and we can use rcu list safely here. + */ list_for_each_entry_rcu(hook, list, node) { unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK; if ((comment & ~hook->mask) == hook->imm) fn = hook->fn; } - rcu_read_unlock(); return fn ? fn(regs, esr) : DBG_HOOK_ERROR; }