From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: ACJfBosGoEHgGmCQqrJvz7/ubP/woerYJ938rRMCyr4DdBF5fd5qIgS3uLbj64vmlLMZ9St6i6Hk ARC-Seal: i=1; a=rsa-sha256; t=1516269585; cv=none; d=google.com; s=arc-20160816; b=wu+aHVfESgcXQYHHNEUE38r3vB59s8SRijK6weEDskJPg2/Pm2LJ6vScl/JkLvX3+y YCQbMu2vAwiRn1I8SyVfNpUQRlFkNeec8wKOEROhh9GpqdG/CKQggJIskdCg4AqqtjPi zwP9kLivWSyGaadIN6md5gRM8bHUoYgVa3e+vRFDAc82Hb405fTJoodapi7NGePJAmLE racDSgPqpXRDy5B8bH/kVSxi/osXrMU1Q5SJ9+MLgVLscUNwHw6BMXgw+wqeSEWV6FH1 P0VN2bVjptKIYY8ZAvANZcDxI6mFlrBn7fOlmhwuc90pyO0lfiDYqRKzch3aP6jkSTq7 gp4A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=spamdiagnosticmetadata:spamdiagnosticoutput :content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :dkim-signature:arc-authentication-results; bh=qb4VcDoE8V6Q/3ZQl5eJUOD/knpXCZO6QKTzI3Lmn4c=; b=eZmZbNZE67dQFMt2Mv+5I0zGgIQWv5wQ8KW9icECFd09LuyVyJ3KK8qQxCGrwk2Y+r P+mqyHA6Kg9kTAj9c0iYTIIE/s79pH7W8s6BJJ6/mjN0Ahu6B2BBi0ejP6Ywp7CgyMKf Bwf/eG/yV2ndzKwFCdGkRqRAo7bQNaX2MQ9Q8S0q+p7vywxeVgOhDMZxrBeYBt1KUwHu 7WOljlVnS3mByXFj2G9SV2U77uBWJcubdNJItMWssY15/5zK9NO3/W+3tkibyJFqkCMz Iu0cCpYHYIon9ojcIIqrUi1o4JEtn3Ce/HgaDuCnfjrQb24EsfJXL49y/Lhbp/kP/i// 9lIw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@virtuozzo.com header.s=selector1 header.b=W+lizQaw; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 104.47.2.130 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Authentication-Results: mx.google.com; dkim=pass header.i=@virtuozzo.com header.s=selector1 header.b=W+lizQaw; spf=pass (google.com: domain of ktkhai@virtuozzo.com designates 104.47.2.130 as permitted sender) smtp.mailfrom=ktkhai@virtuozzo.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=virtuozzo.com Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=ktkhai@virtuozzo.com; Subject: Re: [PATCH v2 1/3] Revert "do_SAK: Don't recursively take the tasklist_lock" To: "Eric W. Biederman" Cc: gregkh@linuxfoundation.org, jslaby@suse.com, oleg@redhat.com, linux-kernel@vger.kernel.org References: <151619233415.5683.18062849657787533510.stgit@localhost.localdomain> <151619277281.5683.16110625178528288163.stgit@localhost.localdomain> <87shb4floe.fsf@xmission.com> From: Kirill Tkhai Message-ID: <1efc4393-cf08-e30e-b6c1-bdeada1d8590@virtuozzo.com> Date: Thu, 18 Jan 2018 12:59:38 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <87shb4floe.fsf@xmission.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [195.214.232.6] X-ClientProxiedBy: AM5PR0701CA0024.eurprd07.prod.outlook.com (2603:10a6:203:51::34) To AM5PR0801MB1330.eurprd08.prod.outlook.com (2603:10a6:203:1f::8) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 9923e9ee-2022-4312-9248-08d55e5a31cb X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(5600026)(4604075)(2017052603307)(7153060)(7193020);SRVR:AM5PR0801MB1330; 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Biederman wrote: > Kirill Tkhai writes: > >> This reverts commit 20ac94378de5. >> >> send_sig() does not take tasklist_lock for a long time, >> so this commit and the problem it solves are not relevant >> anymore. >> >> Also, the problem of force_sig() is it clears SIGNAL_UNKILLABLE >> flag, thus even global init may be killed by __do_SAK(), >> which is definitely not the expected behavior. > > Actually it is. > > SAK should kill everything that has the tty open. If init opens the tty > I am so sorry, it can not operate correctly. init should not have your > tty open. > > The alternative and perhaps the better option is to simply remove SAK > support, if we can not make it race free. > > But yes SAK very much does care about races. As Oleg pointed, this patch does not introduce new races in comparison to what we have now. Please, look at the discussion we started here: https://lkml.org/lkml/2018/1/12/171. You wasn't in CC, as there was not reverted your patch 20ac94378de5. Oleg suggested an accurate way to revert the commit firstly before doing all the things, because currently there is an ambiguity with force_sig() and send_sig() in the single function. My patch introduces uniformity in the function. > >> Came from discussion in "tty: Iterate only thread group leaders in __do_SAK()" >> https://lkml.org/lkml/2018/1/11/492 >> >> Suggested-by: Oleg Nesterov >> Signed-off-by: Kirill Tkhai >> --- >> drivers/tty/tty_io.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c >> index dc60aeea87d8..84715ba1aee2 100644 >> --- a/drivers/tty/tty_io.c >> +++ b/drivers/tty/tty_io.c >> @@ -2737,7 +2737,7 @@ void __do_SAK(struct tty_struct *tty) >> if (i != 0) { >> tty_notice(tty, "SAK: killed process %d (%s): by fd#%d\n", >> task_pid_nr(p), p->comm, i - 1); >> - force_sig(SIGKILL, p); >> + send_sig(SIGKILL, p, 1); >> } >> task_unlock(p); >> } while_each_thread(g, p);