From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9531C433EF for ; Tue, 10 May 2022 15:05:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345507AbiEJPJP (ORCPT ); Tue, 10 May 2022 11:09:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39822 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345615AbiEJPIv (ORCPT ); Tue, 10 May 2022 11:08:51 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 307132E6A9; Tue, 10 May 2022 07:38:29 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1652193507; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=w3ElTKcPgRcfhSXCODsdQ9SYsvPTENqPkhqSJjkaUnk=; b=2FSm4oOqMOc7u7DOArxh7vypRuFLzQJ4f5e7uumNWZk1I+wP6rN1Z+BamxxgNm/HkkJ8dS jbuzVvdMTYuHKMYIdn3pJkzvOHvrtKjxkW5KQCOiLLd87+XgT1YCNZ7cZ3D75oQSIjPAbJ 3MI6F+cGiQbGDDLe0QmgNkbGSBVbUVM5Is/ozOGVwpE47NGGUx6NXo3tJweiXw1f2yIHV9 f3oKOyk0z/V2PomejDHplZTRKP9rSVl69cpaHnnuluzzxUokX3JCs5rygHZql3fiIvNDkg QQKtbUKUOoW1hWOjc4Wij3nCbiFffRmPCss0ja1b96xfU7R1+MpTAUbvCEhisA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1652193507; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=w3ElTKcPgRcfhSXCODsdQ9SYsvPTENqPkhqSJjkaUnk=; b=uPf15/pRgDbttbexXqULpEddKepYTDu4nFjxb45VjXxHv5/WFbZRbyE2QG0KSbWW24RYCN +ZKev2VYi08SYNDg== To: "Eric W. Biederman" , linux-arch@vger.kernel.org Cc: Tejun Heo , Peter Zijlstra , Vincent Guittot , Al Viro , Jens Axboe , Linus Torvalds , linux-kernel@vger.kernel.org, "Eric W. Biederman" , stable@vger.kernel.org, =?utf-8?B?0JzQsNC60YHQuNC8INCa0YPRgtGP0LLQuNC9?= Subject: Re: [PATCH 1/7] kthread: Don't allocate kthread_struct for init and umh In-Reply-To: <20220506141512.516114-1-ebiederm@xmission.com> References: <87mtfu4up3.fsf@email.froward.int.ebiederm.org> <20220506141512.516114-1-ebiederm@xmission.com> Date: Tue, 10 May 2022 16:38:27 +0200 Message-ID: <87fslhpi58.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 06 2022 at 09:15, Eric W. Biederman wrote: > * the init task will end up wanting to create kthreads, which, if > * we schedule it before we create kthreadd, will OOPS. > */ > - pid = kernel_thread(kernel_init, NULL, CLONE_FS); > + pid = user_mode_thread(kernel_init, NULL, CLONE_FS); So init does not have PF_KTHREAD set anymore, which causes this to go sideways with a NULL pointer dereference in get_mm_counter() on next: get_mm_counter include/linux/mm.h:1996 [inline] get_mm_rss include/linux/mm.h:2049 [inline] task_nr_scan_windows.isra.0+0x23/0x120 kernel/sched/fair.c:1123 task_scan_min kernel/sched/fair.c:1144 [inline] task_scan_start+0x6c/0x400 kernel/sched/fair.c:1150 task_tick_numa kernel/sched/fair.c:2944 [inline] task_tick_fair+0xaeb/0xef0 kernel/sched/fair.c:11186 scheduler_tick+0x20a/0x5e0 kernel/sched/core.c:5380 https://lore.kernel.org/lkml/0000000000008a9fbb05dea76400@google.com because the fence in task_tick_numa(): if ((curr->flags & (PF_EXITING | PF_KTHREAD)) || work->next != work) return; is not longer sufficient. It needs also to bail if !curr->mm. I'm worried that there are more of these issues lurking. Haven't looked yet. Thanks, tglx