From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH v1 1/2] pid: add pidfd_open() Date: Thu, 16 May 2019 17:06:12 +0200 Message-ID: <20190516150611.GC22564@redhat.com> References: <20190516135944.7205-1-christian@brauner.io> <20190516142659.GB22564@redhat.com> <20190516145607.j43xyj26k6l5vmbd@yavin> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190516145607.j43xyj26k6l5vmbd@yavin> Sender: linux-kernel-owner@vger.kernel.org To: Aleksa Sarai Cc: Christian Brauner , jannh@google.com, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, arnd@arndb.de, akpm@linux-foundation.org, dhowells@redhat.com, ebiederm@xmission.com, elena.reshetova@intel.com, keescook@chromium.org, luto@amacapital.net, luto@kernel.org, tglx@linutronix.de, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, joel@joelfernandes.orgda List-Id: linux-api@vger.kernel.org On 05/17, Aleksa Sarai wrote: > > On 2019-05-16, Oleg Nesterov wrote: > > On 05/16, Christian Brauner wrote: > > > > > > With the introduction of pidfds through CLONE_PIDFD it is possible to > > > created pidfds at process creation time. > > > > Now I am wondering why do we need CLONE_PIDFD, you can just do > > > > pid = fork(); > > pidfd_open(pid); > > While the race window would be exceptionally short, there is the > possibility that the child will die Yes, > and their pid will be recycled > before you do pidfd_open(). No. Unless the caller's sub-thread does wait() before pidfd_open(), of course. Or unless you do signal(SIGCHILD, SIG_IGN). Oleg.