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Biederman) To: Oleg Nesterov Cc: =?utf-8?Q?J=C3=BCrg?= Billeter , Andrew Morton , Thomas Gleixner , Kees Cook , Andy Lutomirski , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org References: <20181127225408.7553-1-j@bitron.ch> <20181127225408.7553-2-j@bitron.ch> <20181128144230.GG30395@redhat.com> Date: Wed, 28 Nov 2018 09:23:39 -0600 In-Reply-To: <20181128144230.GG30395@redhat.com> (Oleg Nesterov's message of "Wed, 28 Nov 2018 15:42:31 +0100") Message-ID: <87r2f5gr9g.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1gS1gt-0000Ak-0W;;;mid=<87r2f5gr9g.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=67.3.154.154;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19ZIhrxRrHeEu/P26ASig1IcfQQ3S/A0H0= X-SA-Exim-Connect-IP: 67.3.154.154 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa04.xmission.com X-Spam-Level: * X-Spam-Status: No, score=1.0 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,TVD_RCVD_IP,T_TM2_M_HEADER_IN_MSG,T_TooManySym_01, T_TooManySym_02,T_TooManySym_03,XMGappySubj_01,XMSubLong autolearn=disabled version=3.4.2 X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.5000] * 0.7 XMSubLong Long Subject * 0.5 XMGappySubj_01 Very gappy subject * 0.0 TVD_RCVD_IP Message was received from an IP address * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.0 T_TooManySym_03 6+ unique symbols in subject * 0.0 T_TooManySym_02 5+ unique symbols in subject X-Spam-DCC: XMission; sa04 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: *;Oleg Nesterov X-Spam-Relay-Country: X-Spam-Timing: total 229 ms - load_scoreonly_sql: 0.05 (0.0%), signal_user_changed: 2.6 (1.2%), b_tie_ro: 1.88 (0.8%), parse: 0.92 (0.4%), extract_message_metadata: 2.9 (1.3%), get_uri_detail_list: 0.84 (0.4%), tests_pri_-1000: 3.9 (1.7%), tests_pri_-950: 1.25 (0.5%), tests_pri_-900: 1.00 (0.4%), tests_pri_-90: 17 (7.3%), check_bayes: 15 (6.7%), b_tokenize: 4.8 (2.1%), b_tok_get_all: 4.9 (2.1%), b_comp_prob: 1.61 (0.7%), b_tok_touch_all: 2.5 (1.1%), b_finish: 0.58 (0.3%), tests_pri_0: 185 (80.8%), check_dkim_signature: 0.55 (0.2%), check_dkim_adsp: 2.4 (1.0%), poll_dns_idle: 0.83 (0.4%), tests_pri_10: 1.84 (0.8%), tests_pri_500: 5 (2.3%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH] prctl: add PR_{GET,SET}_KILL_DESCENDANTS_ON_EXIT X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On 11/27, Jürg Billeter wrote: >> >> @@ -704,6 +713,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead) >> struct task_struct *p, *n; >> LIST_HEAD(dead); >> >> + if (group_dead && tsk->signal->kill_descendants_on_exit) >> + walk_process_tree(tsk, kill_descendant_visitor, NULL); > > Well, this is not exactly right, at least this is suboptimal in that > other sub-threads can too call walk_process_tree(kill_descendant_visitor) > later for no reason. Oleg I think I am missing something. Reading kernel/exit.c I see "group_dead = atomic_dec_and_test(&tsk->signal->live)". Which seems like enough to ensure exactly one task/thread calls walk_process_tree. Can you explain what I am missing? Eric