From mboxrd@z Thu Jan 1 00:00:00 1970 From: Enke Chen Subject: Re: [PATCH] kernel/signal: Signal-based pre-coredump notification Date: Tue, 16 Oct 2018 17:39:48 -0700 Message-ID: References: <20181015120521.GA10146@redhat.com> <20398328-4ee1-96b2-5723-4b7eed55f0a2@cisco.com> <20181016141405.GA22045@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181016141405.GA22045@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Oleg Nesterov Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Arnd Bergmann , "Eric W. Biederman" , Khalid Aziz , Kate Stewart , Helge Deller , Greg Kroah-Hartman , Al Viro , Andrew Morton , Christian Brauner , Catalin Marinas , Will Deacon , Dave Martin , Mauro Carvalho Chehab , Michal Hocko , Rik List-Id: linux-arch.vger.kernel.org Hi, Oleg: On 10/16/18 7:14 AM, Oleg Nesterov wrote: > On 10/15, Enke Chen wrote: >> >>> I don't understand why we need valid_predump_signal() at all. >> >> Most of the signals have well-defined semantics, and would not be appropriate >> for this purpose. > > you are going to change the rules anyway. > >> That is why it is limited to only SIGCHLD, SIGUSR1, SIGUSR2. > > Which do not queue. So the parent won't get the 2nd signal if 2 children > crash at the same time. > >>>> if (sig_kernel_coredump(signr)) { >>>> + /* >>>> + * Notify the parent prior to the coredump if the >>>> + * parent is interested in such a notificaiton. >>>> + */ >>>> + int p_sig = current->real_parent->predump_signal; >>>> + >>>> + if (valid_predump_signal(p_sig)) { >>>> + read_lock(&tasklist_lock); >>>> + do_notify_parent_predump(current); >>>> + read_unlock(&tasklist_lock); >>>> + cond_resched(); >>> >>> perhaps this should be called by do_coredump() after coredump_wait() kills >>> all the sub-threads? >> >> proc_coredump_connector(current) is located here, they should stay together. > > Why? > > Once again, other threads are still alive. So if the parent restarts the service > after it recieves -predump_signal, the new process can "race" with the old thread. Yes, it is a good idea to do the signal notification in do_coredump() after coredump_wait(). Will make the change as suggested. Thanks. -- Enke From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from alln-iport-2.cisco.com ([173.37.142.89]:46104 "EHLO alln-iport-2.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727171AbeJQIcy (ORCPT ); Wed, 17 Oct 2018 04:32:54 -0400 Subject: Re: [PATCH] kernel/signal: Signal-based pre-coredump notification References: <20181015120521.GA10146@redhat.com> <20398328-4ee1-96b2-5723-4b7eed55f0a2@cisco.com> <20181016141405.GA22045@redhat.com> From: Enke Chen Message-ID: Date: Tue, 16 Oct 2018 17:39:48 -0700 MIME-Version: 1.0 In-Reply-To: <20181016141405.GA22045@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Oleg Nesterov Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Arnd Bergmann , "Eric W. Biederman" , Khalid Aziz , Kate Stewart , Helge Deller , Greg Kroah-Hartman , Al Viro , Andrew Morton , Christian Brauner , Catalin Marinas , Will Deacon , Dave Martin , Mauro Carvalho Chehab , Michal Hocko , Rik van Riel , "Kirill A. Shutemov" , Roman Gushchin , Marcos Paulo de Souza , Dominik Brodowski , Cyrill Gorcunov , Yang Shi , Jann Horn , Kees Cook , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "Victor Kamensky (kamensky)" , xe-linux-external@cisco.com, Stefan Strogin , Eugene Syromiatnikov , Enke Chen Message-ID: <20181017003948.3ppwHkPDP9zU0HsQSaKBTy0wgknWda4eDLh-ywEpTAI@z> Hi, Oleg: On 10/16/18 7:14 AM, Oleg Nesterov wrote: > On 10/15, Enke Chen wrote: >> >>> I don't understand why we need valid_predump_signal() at all. >> >> Most of the signals have well-defined semantics, and would not be appropriate >> for this purpose. > > you are going to change the rules anyway. > >> That is why it is limited to only SIGCHLD, SIGUSR1, SIGUSR2. > > Which do not queue. So the parent won't get the 2nd signal if 2 children > crash at the same time. > >>>> if (sig_kernel_coredump(signr)) { >>>> + /* >>>> + * Notify the parent prior to the coredump if the >>>> + * parent is interested in such a notificaiton. >>>> + */ >>>> + int p_sig = current->real_parent->predump_signal; >>>> + >>>> + if (valid_predump_signal(p_sig)) { >>>> + read_lock(&tasklist_lock); >>>> + do_notify_parent_predump(current); >>>> + read_unlock(&tasklist_lock); >>>> + cond_resched(); >>> >>> perhaps this should be called by do_coredump() after coredump_wait() kills >>> all the sub-threads? >> >> proc_coredump_connector(current) is located here, they should stay together. > > Why? > > Once again, other threads are still alive. So if the parent restarts the service > after it recieves -predump_signal, the new process can "race" with the old thread. Yes, it is a good idea to do the signal notification in do_coredump() after coredump_wait(). Will make the change as suggested. Thanks. -- Enke