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=-11.1 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL autolearn=no 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 BDC20CA9EAE for ; Tue, 29 Oct 2019 11:50:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90A2D21D56 for ; Tue, 29 Oct 2019 11:50:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pE6dlCmk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387622AbfJ2LuJ (ORCPT ); Tue, 29 Oct 2019 07:50:09 -0400 Received: from mail-wm1-f65.google.com ([209.85.128.65]:55382 "EHLO mail-wm1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727799AbfJ2LuJ (ORCPT ); Tue, 29 Oct 2019 07:50:09 -0400 Received: by mail-wm1-f65.google.com with SMTP id g24so2219684wmh.5 for ; Tue, 29 Oct 2019 04:50:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Kd8KdBaTWWYCGSiSX2Hi1YoJKfTLqZTdgxbJDT6peN8=; b=pE6dlCmkPr6YeNj8F0dlfkhzBt/HHIIhk3RN50cwbOPLGkWPqHt/1iODkRlGyHLyFq dK9Q6Ar+3plcJj7JvIq7dvsb3DSLrw5T2HkFAHQhsmFUPm5o57kp69d4EyMGyH2Le2Xw Jdx/CK56+iBVpo0aCK38aMZXSv2kgZHjfqw7eHcroAqkJ9G8mkC6fDHNFlRSEsgEELzZ Bez8pVOdYrspy/rtQ+OtUP2wXowd5LMZluXxH6OcHVE4Wa4NqM7Px4E1GZvfuRZ256bu sdVTZ1C+hweBiMR/1t5X9TgWfC4UoiM6sf/5L8krxnzl6VsosKkGLXZ2rZn+Mvn5HNAb aCCA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=Kd8KdBaTWWYCGSiSX2Hi1YoJKfTLqZTdgxbJDT6peN8=; b=lTDqeyRwJ6Y2MHBGPXbtkxLVWTUtqaszTklKwEyh3bYM9DlzE4RnPRo10q0wdNxqZv Wn+Ajjsyo1MWPS2r9Yj+o/2RhS4MQA3GS/C+bSbl6X4D4WVShYB6nfZ+XfkwojhBYfr1 SsSKkRpnEdsoZv+4u8dyKxnrVRPQEU0LsdX9ZP1GoZg+hsomNosTCzocAokol1/0C+zh P9EQYCqk96m9sIYlg3uru8/0vwkd29yJup8PqKT3Scq829Bxkt7RxO4ij1DrwJLyTcZi soK4HGML2YX+X/Sw6DLyBmXa/dyVtEoF3qCr/71Yj96RdCsau+AuHfqZji5cIvg6IKI9 tUVQ== X-Gm-Message-State: APjAAAX8IWuGkFNFDPxjYzZDjZFPG4CRTtWr1MRPuqsVUISDIsTupcTJ pvesncUrgjMK3N32hqJMnjywdQ== X-Google-Smtp-Source: APXvYqwIteS+juQJ8rYOHhGQ1aepL/UWGhYPMUVt3OSt1PPedjqfm4WJtCsinIek6PWiKVm5qXubVQ== X-Received: by 2002:a7b:c954:: with SMTP id i20mr3818938wml.60.1572349805183; Tue, 29 Oct 2019 04:50:05 -0700 (PDT) Received: from google.com ([2a00:79e0:d:110:d6cc:2030:37c1:9964]) by smtp.gmail.com with ESMTPSA id d16sm3260781wmb.27.2019.10.29.04.50.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Oct 2019 04:50:04 -0700 (PDT) Date: Tue, 29 Oct 2019 11:50:00 +0000 From: Quentin Perret To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, aaron.lwe@gmail.com, valentin.schneider@arm.com, mingo@kernel.org, pauld@redhat.com, jdesfossez@digitalocean.com, naravamudan@digitalocean.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, kernel-team@android.com, john.stultz@linaro.org Subject: Re: NULL pointer dereference in pick_next_task_fair Message-ID: <20191029115000.GA11194@google.com> References: <20191028174603.GA246917@google.com> <20191029113411.GP4643@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191029113411.GP4643@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 29 Oct 2019 at 12:34:11 (+0100), Peter Zijlstra wrote: > On Mon, Oct 28, 2019 at 05:46:03PM +0000, Quentin Perret wrote: > > The issue is very transient and relatively hard to reproduce. > > > > After digging a bit, the offending commit seems to be: > > > > 67692435c411 ("sched: Rework pick_next_task() slow-path") > > > > By 'offending' I mean that reverting it makes the issue go away. The > > issue comes from the fact that pick_next_entity() returns a NULL se in > > the 'simple' path of pick_next_task_fair(), which causes obvious > > problems in the subsequent call to set_next_entity(). > > > > I'll dig more, but if anybody understands the issue in the meatime feel > > free to send me a patch to try out :) > > Can you please see if this makes any difference? > > --- > kernel/sched/core.c | 6 ++++-- > kernel/sched/fair.c | 2 +- > kernel/sched/idle.c | 3 +-- > 3 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7880f4f64d0e..abd2d4f80381 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3922,8 +3922,10 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) > goto restart; > > /* Assumes fair_sched_class->next == idle_sched_class */ > - if (unlikely(!p)) > - p = idle_sched_class.pick_next_task(rq, prev, rf); > + if (unlikely(!p)) { > + prev->sched_class->put_prev_task(rq, prev, rf); > + p = idle_sched_class.pick_next_task(rq, NULL, NULL); > + } > > return p; > } > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 83ab35e2374f..2aad94bb7165 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6820,7 +6820,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf > simple: > #endif > if (prev) > - put_prev_task(rq, prev); > + prev->sched_class->put_prev_task(rq, prev, rf); > > do { > se = pick_next_entity(cfs_rq, NULL); > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index 8dad5aa600ea..e8dfc84f375a 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -390,8 +390,7 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf > { > struct task_struct *next = rq->idle; > > - if (prev) > - put_prev_task(rq, prev); > + WARN_ON_ONCE(prev || rf); > > set_next_task_idle(rq, next); > > Unfortunately the issue went into hiding this morning and I struggle to reproduce it (this is turning bordeline nightmare now TBH). I'll try the patch once my reproducer is fixed :/ Thank you very much for the help, Quentin