From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Date: Tue, 03 May 2022 13:41:50 +0000 Subject: Re: [PATCH v2 07/12] ptrace: Don't change __state Message-Id: <20220503134149.GA22999@redhat.com> List-Id: References: <87k0b7v9yk.fsf_-_@email.froward.int.ebiederm.org> <20220429214837.386518-7-ebiederm@xmission.com> <20220502153934.GD17276@redhat.com> <87levjrixl.fsf@email.froward.int.ebiederm.org> In-Reply-To: <87levjrixl.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , 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 On 05/02, Eric W. Biederman wrote: > > Oleg Nesterov writes: > > >> #define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE) > >> #define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED) > >> -#define TASK_TRACED (TASK_WAKEKILL | __TASK_TRACED) > >> +#define TASK_TRACED __TASK_TRACED > > ... > >> static inline void signal_wake_up(struct task_struct *t, bool resume) > >> { > >> - signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0); > >> + unsigned int state = 0; > >> + if (resume) { > >> + state = TASK_WAKEKILL; > >> + if (!(t->jobctl & JOBCTL_PTRACE_FROZEN)) > >> + state |= __TASK_TRACED; > >> + } > >> + signal_wake_up_state(t, state); > > > > Can't understand why is this better than the previous version which removed > > TASK_WAKEKILL if resume... Looks a bit strange to me. But again, I didn't > > look at the next patches yet. > > The goal is to replace the existing mechanism with an equivalent one, > so that we don't have to be clever and deal with it being slightly > different in one case. > > The difference is how does signal_pending_state affect how schedule will > sleep in ptrace_stop. But why is it bad if the tracee doesn't sleep in schedule ? If it races with SIGKILL. I still can't understand this. Yes, wait_task_inactive() can fail, so you need to remove WARN_ON_ONCE() in 11/12. Why is removing TASK_WAKEKILL from TASK_TRACED and complicating *signal_wake_up() better? And even if we need to ensure the tracee will always block after ptrace_freeze_traced(), we can change signal_pending_state() to return false if JOBCTL_PTRACE_FROZEN. Much simpler, imo. But still looks unnecessary to me. > Peter's plans to fix PREEMPT_RT or the freezer wait_task_inactive needs > to cope with the final being changed by something else. (TASK_FROZEN in > the freezer case). I can only see that happening by removing the > dependency on the final state in wait_task_inactive. Which we can't do > if we depend on wait_task_inactive failing if the process is in the > wrong state. OK, I guess this is what I do not understand. Could you spell please? And speaking of RT, wait_task_inactive() still can fail because cgroup_enter_frozen() takes css_set_lock? And it is called under preempt_disable() ? I don't understand the plan :/ > At a practical level I think it also has an impact on patch: > "10/12 ptrace: Only return signr from ptrace_stop if it was provided". I didn't look at JOBCTL_PTRACE_SIGNR yet. But this looks minor to me, I mean, I am not sure it worth the trouble. Oleg.