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[91.64.247.236]) by smtp.gmail.com with ESMTPSA id p43sm13593173edc.3.2019.07.25.03.40.07 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 25 Jul 2019 03:40:07 -0700 (PDT) Date: Thu, 25 Jul 2019 12:40:06 +0200 From: Christian Brauner To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, joel@joelfernandes.org, tglx@linutronix.de, tj@kernel.org, dhowells@redhat.com, jannh@google.com, luto@kernel.org, akpm@linux-foundation.org, cyphar@cyphar.com, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, kernel-team@android.com, Ingo Molnar , Peter Zijlstra , linux-api@vger.kernel.org Subject: Re: [PATCH 4/5] pidfd: add CLONE_WAIT_PID Message-ID: <20190725104006.7myahvjtnbcgu3in@brauner.io> References: <20190724144651.28272-1-christian@brauner.io> <20190724144651.28272-5-christian@brauner.io> <20190725103543.GF4707@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190725103543.GF4707@redhat.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 25, 2019 at 12:35:44PM +0200, Oleg Nesterov wrote: > On 07/24, Christian Brauner wrote: > > > > If CLONE_WAIT_PID is set the newly created process will not be > > considered by process wait requests that wait generically on children > > such as: > > I have to admit this feature looks a bit exotic to me... It might look like it from the kernels perspective but from the feedback on this when presenting on this userspace has real usecases for this. > > > --- a/kernel/exit.c > > +++ b/kernel/exit.c > > @@ -1019,6 +1019,9 @@ eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p) > > if (!eligible_pid(wo, p)) > > return 0; > > > > + if ((p->flags & PF_WAIT_PID) && (wo->wo_type != PIDTYPE_PID)) > > + return 0; > > Even if ptrace == T ? > > This doesn't look right. Say, strace should work even if its tracee (or > one of the tracees) has PF_WAIT_PID. As in if (!ptrace && (p->flags & PF_WAIT_PID) && (wo->wo_type != PIDTYPE_PID)) return 0; Sure, we can allow that. Christian