From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754858AbdBEUak (ORCPT + 2 others); Sun, 5 Feb 2017 15:30:40 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:27410 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752120AbdBETWg (ORCPT ); Sun, 5 Feb 2017 14:22:36 -0500 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: Will Deacon , Willy Tarreau Subject: [PATCH 3.10 061/319] arm64: debug: avoid resetting stepping state machine when TIF_SINGLESTEP Date: Sun, 5 Feb 2017 20:20:48 +0100 Message-Id: <1486322486-8024-32-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1486322486-8024-1-git-send-email-w@1wt.eu> References: <1486322486-8024-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: From: Will Deacon commit 3a402a709500c5a3faca2111668c33d96555e35a upstream. When TIF_SINGLESTEP is set for a task, the single-step state machine is enabled and we must take care not to reset it to the active-not-pending state if it is already in the active-pending state. Unfortunately, that's exactly what user_enable_single_step does, by unconditionally setting the SS bit in the SPSR for the current task. This causes failures in the GDB testsuite, where GDB ends up missing expected step traps if the instruction being stepped generates another trap, e.g. PTRACE_EVENT_FORK from an SVC instruction. This patch fixes the problem by preserving the current state of the stepping state machine when TIF_SINGLESTEP is set on the current thread. Cc: Reported-by: Yao Qi Signed-off-by: Will Deacon Signed-off-by: Willy Tarreau --- arch/arm64/kernel/debug-monitors.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index f4726dc..49e6e30 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -276,8 +276,10 @@ int kernel_active_single_step(void) /* ptrace API */ void user_enable_single_step(struct task_struct *task) { - set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); - set_regs_spsr_ss(task_pt_regs(task)); + struct thread_info *ti = task_thread_info(task); + + if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) + set_regs_spsr_ss(task_pt_regs(task)); } void user_disable_single_step(struct task_struct *task) -- 2.8.0.rc2.1.gbe9624a