From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1o91Jm-007mqF-Ay for linux-um@lists.infradead.org; Wed, 06 Jul 2022 09:27:35 +0000 From: Sven Schnelle Subject: Re: [PATCH v4 12/12] sched,signal,ptrace: Rework TASK_TRACED, TASK_STOPPED state References: <87a6bv6dl6.fsf_-_@email.froward.int.ebiederm.org> <20220505182645.497868-12-ebiederm@xmission.com> <877d5ajesi.fsf@email.froward.int.ebiederm.org> <20220628191541.34a073fc@gandalf.local.home> Date: Wed, 06 Jul 2022 11:27:05 +0200 In-Reply-To: (Peter Zijlstra's message of "Wed, 6 Jul 2022 10:59:00 +0200") Message-ID: MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Peter Zijlstra Cc: Steven Rostedt , Alexander Gordeev , "Eric W. Biederman" , linux-kernel@vger.kernel.org, rjw@rjwysocki.net, Oleg Nesterov , mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org Peter Zijlstra writes: > On Wed, Jul 06, 2022 at 09:58:55AM +0200, Sven Schnelle wrote: > >> >> [ 86.218551] kill_chi-343805 6d.... 79990141us : ptrace_stop: JOBCTL_TRACED already set, state=0 <------ valid combination of flags? >> > >> > Yeah, that's not supposed to be so. JOBCTL_TRACED is supposed to follow >> > __TASK_TRACED for now. Set when __TASK_TRACED, cleared when >> > TASK_RUNNING. >> > >> > Specifically {ptrace_,}signal_wake_up() in signal.h clear JOBCTL_TRACED >> > when they would wake a __TASK_TRACED task. >> >> try_to_wake_up() clears TASK_TRACED in this case because a signal >> (SIGKILL) has to be delivered. As a test I put the following change >> on top, and it "fixes" the problem: >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index da0bf6fe9ecd..f2e0f5e70e77 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -4141,6 +4149,9 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) >> * TASK_WAKING such that we can unlock p->pi_lock before doing the >> * enqueue, such as ttwu_queue_wakelist(). >> */ >> + if (p->__state & TASK_TRACED) >> + trace_printk("clearing TASK_TRACED 2\n"); >> + p->jobctl &= ~JOBCTL_TRACED; >> WRITE_ONCE(p->__state, TASK_WAKING); >> >> /* >> >> There are several places where the state is changed from TASK_TRACED to >> something else without clearing JOBCTL_TRACED. > > I'm having difficulty spotting them; I find: > > TASK_WAKEKILL: signal_wake_up() > __TASK_TRACED: ptrace_signal_wake_up(), ptrace_unfreeze_traced(), ptrace_resume() > > And all those sites dutifully clear JOBCTL_TRACED. > > I'd be most interested in the calstack for the 'clearing TASK_TRACED 2' > events to see where we miss a spot. The calltrace is: [ 9.863613] Call Trace: [ 9.863616] [<00000000d3105f0e>] try_to_wake_up+0xae/0x620 [ 9.863620] ([<00000000d3106164>] try_to_wake_up+0x304/0x620) [ 9.863623] [<00000000d30d1e46>] ptrace_unfreeze_traced+0x9e/0xa8 [ 9.863629] [<00000000d30d2ef0>] __s390x_sys_ptrace+0xc0/0x160 [ 9.863633] [<00000000d3c5d8f4>] __do_syscall+0x1d4/0x200 [ 9.863678] [<00000000d3c6c332>] system_call+0x82/0xb0 [ 9.863685] Last Breaking-Event-Address: [ 9.863686] [<00000000d3106176>] try_to_wake_up+0x316/0x620 [ 9.863688] ---[ end trace 0000000000000000 ]--- ptrace_unfreeze_traced() is: static void ptrace_unfreeze_traced(struct task_struct *task) { unsigned long flags; /* * The child may be awake and may have cleared * JOBCTL_PTRACE_FROZEN (see ptrace_resume). The child will * not set JOBCTL_PTRACE_FROZEN or enter __TASK_TRACED anew. */ if (lock_task_sighand(task, &flags)) { task->jobctl &= ~JOBCTL_PTRACE_FROZEN; if (__fatal_signal_pending(task)) { task->jobctl &= ~TASK_TRACED; Looking at this, shouldn't the line above read task->jobctl &= ~JOBCTL_TRACED? wake_up_state(task, __TASK_TRACED); } unlock_task_sighand(task, &flags); } } _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um