From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Nesterov Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification Date: Fri, 26 Oct 2018 10:28:13 +0200 Message-ID: <20181026082812.GA10581@redhat.com> References: <458c04d8-d189-4a26-729a-bb1d1d751534@cisco.com> <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com> <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> Sender: linux-kernel-owner@vger.kernel.org To: Enke Chen Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , 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 List-Id: linux-arch.vger.kernel.org On 10/25, Enke Chen wrote: > > +static void do_notify_parent_predump(void) > +{ > + struct task_struct *parent; > + int sig; > + > + read_lock(&tasklist_lock); > + parent = current->parent; > + sig = parent->signal->predump_signal; > + if (sig != 0) > + do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID); > + read_unlock(&tasklist_lock); Ah. It is strange I didn't think about this before... Please, do not take tasklist_lock, use rcu_read_lock() instead. do_send_sig_info() uses the rcu-friendly lock_task_sighand(), so rcu_dereference(parent) should work fine. Oleg. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:45724 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725914AbeJZRE3 (ORCPT ); Fri, 26 Oct 2018 13:04:29 -0400 Date: Fri, 26 Oct 2018 10:28:13 +0200 From: Oleg Nesterov Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification Message-ID: <20181026082812.GA10581@redhat.com> References: <458c04d8-d189-4a26-729a-bb1d1d751534@cisco.com> <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com> <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Enke Chen Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , 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 , x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "Victor Kamensky (kamensky)" , xe-linux-external@cisco.com, Stefan Strogin Message-ID: <20181026082813.PRjQLMg2eOYYjdKDsB1ExSC8cHjShWMJW4E_tbazcJ8@z> On 10/25, Enke Chen wrote: > > +static void do_notify_parent_predump(void) > +{ > + struct task_struct *parent; > + int sig; > + > + read_lock(&tasklist_lock); > + parent = current->parent; > + sig = parent->signal->predump_signal; > + if (sig != 0) > + do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID); > + read_unlock(&tasklist_lock); Ah. It is strange I didn't think about this before... Please, do not take tasklist_lock, use rcu_read_lock() instead. do_send_sig_info() uses the rcu-friendly lock_task_sighand(), so rcu_dereference(parent) should work fine. Oleg.