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 X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD800C5CFEB for ; Wed, 11 Jul 2018 07:30:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 715232086B for ; Wed, 11 Jul 2018 07:30:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 715232086B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726360AbeGKHdG (ORCPT ); Wed, 11 Jul 2018 03:33:06 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:34231 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726281AbeGKHdG (ORCPT ); Wed, 11 Jul 2018 03:33:06 -0400 Received: by mail-wr1-f66.google.com with SMTP id c13-v6so16995155wrt.1 for ; Wed, 11 Jul 2018 00:30:12 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=fxRiu7oKmVq6ke/lQ/gq1h8dclx9MILloQReYHWplVE=; b=qvfl9kM5EHXhCceIOgaPJv9tjbXUZr7HcTIDmGzeCVbeXj8Tqq3I1vXvz8jD0CmbAI iFEYfe3P9uLVskKpcYIEyXP0F2Mthz/TAru1NtXgZOgqUUpF/l2bISwTqa4WMvwQmC9b g7PpyEtHyw9rmY8L678KoqJgNVpUmSIKAMfcuMVNenNQKh/nB16YCkkiBB8yu3hWQ7iE dHaTVQjQUE8ZED8cI+ALu2rkkcwAzHYBFCgw/fDGyLB3SR+ShrNTRuw15Xi7mt+5LAXw dve/SXL78BWz+SVQ8BMpHjWGi5HgmbL5tefTm8i20VCHLs2DJitrkxwxYS4PWuIfUbHo /aKA== X-Gm-Message-State: AOUpUlEzgyfhmkTtJRL1tGAqXyXfauUAGQzL9jwbpmvYegxacioS21hz NGW7WuxSo9iQ+C2RSwixPH7Ywg== X-Google-Smtp-Source: AAOMgpdXxflAZ2JRbgOKEX7ty5I8yCU4eyzbOaIL/2ph7jJ7IQyS0oJhwD8lblBtyevgNXgZ8WalOA== X-Received: by 2002:a5d:5088:: with SMTP id a8-v6mr14452722wrt.37.1531294211778; Wed, 11 Jul 2018 00:30:11 -0700 (PDT) Received: from localhost.localdomain.com ([151.15.255.159]) by smtp.gmail.com with ESMTPSA id j11-v6sm19595529wrr.37.2018.07.11.00.30.10 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 11 Jul 2018 00:30:11 -0700 (PDT) From: Juri Lelli To: peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, bristot@redhat.com, Juri Lelli Subject: [PATCH] sched/deadline: Fix switched_from_dl Date: Wed, 11 Jul 2018 09:29:48 +0200 Message-Id: <20180711072948.27061-1-juri.lelli@redhat.com> X-Mailer: git-send-email 2.14.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mark noticed that syzkaller is able to reliably trigger the following dl_rq->running_bw > dl_rq->this_bw WARNING: CPU: 1 PID: 153 at kernel/sched/deadline.c:124 switched_from_dl+0x454/0x608 Kernel panic - not syncing: panic_on_warn set ... CPU: 1 PID: 153 Comm: syz-executor253 Not tainted 4.18.0-rc3+ #29 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x458 show_stack+0x20/0x30 dump_stack+0x180/0x250 panic+0x2dc/0x4ec __warn_printk+0x0/0x150 report_bug+0x228/0x2d8 bug_handler+0xa0/0x1a0 brk_handler+0x2f0/0x568 do_debug_exception+0x1bc/0x5d0 el1_dbg+0x18/0x78 switched_from_dl+0x454/0x608 __sched_setscheduler+0x8cc/0x2018 sys_sched_setattr+0x340/0x758 el0_svc_naked+0x30/0x34 syzkaller reproducer runs a bunch of threads that constantly switch between DEADLINE and NORMAL classes while interacting through futexes. The splat above is caused by the fact that if a DEADLINE task is setattr back to NORMAL while in non_contending state (blocked on a futex - inactive timer armed), its contribution to running_bw is not removed before sub_rq_bw() gets called (!task_on_rq_queued() branch) and the latter sees running_bw > this_bw. Fix it by removing a task contribution from running_bw if the task is not queued and in non_contending state while switched to a different class. Reported-by: Mark Rutland Signed-off-by: Juri Lelli --- kernel/sched/deadline.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index fbfc3f1d368a..10c7b51c0d1f 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2290,8 +2290,17 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p) if (task_on_rq_queued(p) && p->dl.dl_runtime) task_non_contending(p); - if (!task_on_rq_queued(p)) + if (!task_on_rq_queued(p)) { + /* + * Inactive timer is armed. However, p is leaving DEADLINE and + * might migrate away from this rq while continuing to run on + * some other class. We need to remove its contribution from + * this rq running_bw now, or sub_rq_bw (below) will complain. + */ + if (p->dl.dl_non_contending) + sub_running_bw(&p->dl, &rq->dl); sub_rq_bw(&p->dl, &rq->dl); + } /* * We cannot use inactive_task_timer() to invoke sub_running_bw() -- 2.14.4