From mboxrd@z Thu Jan 1 00:00:00 1970 From: Enke Chen Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification Date: Fri, 26 Oct 2018 15:23:47 -0700 Message-ID: <21f678a8-4001-df36-c26e-e96cf203b1b1@cisco.com> References: <458c04d8-d189-4a26-729a-bb1d1d751534@cisco.com> <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com> <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> <20181026082812.GA10581@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181026082812.GA10581@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" , 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 Hi, Olge: This is really a good idea given that "parent" is declared as RCU-protected. Just a bit odd, though, that the "parent" has not been accessed this way in the code base. So just to confirm: the revised code would look like the following: static void do_notify_parent_predump(void) { struct task_struct *parent; int sig; rcu_read_lock(); parent = rcu_dereference(current->parent); sig = parent->signal->predump_signal; if (sig != 0) do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID); rcu_read_unlock(); } Thank you so much for your help during this review. I would like to ack your contribution in the "Reviewed-by:" field. -- Enke On 10/26/18 1:28 AM, Oleg Nesterov wrote: > 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 rcdn-iport-1.cisco.com ([173.37.86.72]:58951 "EHLO rcdn-iport-1.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726418AbeJ0HCl (ORCPT ); Sat, 27 Oct 2018 03:02:41 -0400 Subject: Re: [PATCH v4] kernel/signal: Signal-based pre-coredump notification References: <458c04d8-d189-4a26-729a-bb1d1d751534@cisco.com> <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com> <84460a77-a111-404e-4bad-88104a6e246e@cisco.com> <20181026082812.GA10581@redhat.com> From: Enke Chen Message-ID: <21f678a8-4001-df36-c26e-e96cf203b1b1@cisco.com> Date: Fri, 26 Oct 2018 15:23:47 -0700 MIME-Version: 1.0 In-Reply-To: <20181026082812.GA10581@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" , 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 , Enke Chen Message-ID: <20181026222347.l1CQtt9lWaX_0DqkOX0-qwPWN52g0PM6VDhJ13v5bp8@z> Hi, Olge: This is really a good idea given that "parent" is declared as RCU-protected. Just a bit odd, though, that the "parent" has not been accessed this way in the code base. So just to confirm: the revised code would look like the following: static void do_notify_parent_predump(void) { struct task_struct *parent; int sig; rcu_read_lock(); parent = rcu_dereference(current->parent); sig = parent->signal->predump_signal; if (sig != 0) do_send_sig_info(sig, SEND_SIG_NOINFO, parent, PIDTYPE_TGID); rcu_read_unlock(); } Thank you so much for your help during this review. I would like to ack your contribution in the "Reviewed-by:" field. -- Enke On 10/26/18 1:28 AM, Oleg Nesterov wrote: > 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. >