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=-15.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 36BF6C63777 for ; Thu, 19 Nov 2020 21:35:54 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 993692222A for ; Thu, 19 Nov 2020 21:35:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="lufw7hzp"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="FjzSuS/v" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 993692222A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:Reply-To:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=wZh08VdNEkv4fZFUqrKWDcBi74Rr+Air278rPRiwJfk=; b=lufw7hzppd6yqU2huikMx4GV73 /36DoP88HI6ehRS7OS50nqJsBvCRpP4Lt85lU9wqOMnSUyGEHMtvnuX59G8PHfxWjysmsW2KC/1UJ snuHMUDHFaBYndvertwyIqnc5ZFfuuybCBm9zQ0TyrIUNK5bxOELObUhPJ0rLYuUVVgtf5vuAVmr9 dJjDQVgG7Q8xk3RSr6/WAzur789CZpmoQi8xJIKBnmrCwEW+sBgeJNtCS4f40LRk1c508jWCW95cm PmSe7z9aN80EElSsUI6OkR4i4HjPqz0ZW84mmPhMkLU1ruQor9i1Rr2zLdn+vFPG8LlkLljgLhlSC 1XIF1KZg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfraH-0004Fu-8s; Thu, 19 Nov 2020 21:35:17 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfraE-0004FC-7J for linux-arm-kernel@lists.infradead.org; Thu, 19 Nov 2020 21:35:15 +0000 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CC7352222A; Thu, 19 Nov 2020 21:35:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605821712; bh=WiDazihmUqIbfDQNuj5oVU9c796OAQteSS6DruzFVVQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=FjzSuS/vurox71DLRNzjRg39KsUR34CUpNxVObvX5FV4wv3PP0o64vUT9+Dw1sBzt FZIThnUqycC7x7xGy8L3bjvSkry83weBw4JFoSKDMxC4H5ZktGT+rdSyMoNk2/qJJw tdb98ssEZERXZ0YrzHdwdsHaJxnjjeGk9Fg57cR4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 75FDB35225D3; Thu, 19 Nov 2020 13:35:12 -0800 (PST) Date: Thu, 19 Nov 2020 13:35:12 -0800 From: "Paul E. McKenney" To: Marco Elver Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...) Message-ID: <20201119213512.GB1437@paulmck-ThinkPad-P72> References: <20201113175754.GA6273@paulmck-ThinkPad-P72> <20201117105236.GA1964407@elver.google.com> <20201117182915.GM1437@paulmck-ThinkPad-P72> <20201118225621.GA1770130@elver.google.com> <20201118233841.GS1437@paulmck-ThinkPad-P72> <20201119125357.GA2084963@elver.google.com> <20201119151409.GU1437@paulmck-ThinkPad-P72> <20201119170259.GA2134472@elver.google.com> <20201119184854.GY1437@paulmck-ThinkPad-P72> <20201119193819.GA2601289@elver.google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201119193819.GA2601289@elver.google.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201119_163514_475748_A6133369 X-CRM114-Status: GOOD ( 32.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Cc: Mark Rutland , Anders Roxell , Jann Horn , Peter Zijlstra , Lai Jiangshan , Linux Kernel Mailing List , Steven Rostedt , rcu@vger.kernel.org, Linux-MM , Alexander Potapenko , kasan-dev , Tejun Heo , Andrew Morton , Dmitry Vyukov , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Nov 19, 2020 at 08:38:19PM +0100, Marco Elver wrote: > On Thu, Nov 19, 2020 at 10:48AM -0800, Paul E. McKenney wrote: > > On Thu, Nov 19, 2020 at 06:02:59PM +0100, Marco Elver wrote: [ . . . ] > > > I can try bisection again, or reverting some commits that might be > > > suspicious? But we'd need some selection of suspicious commits. > > > > The report claims that one of the rcu_node ->lock fields is held > > with interrupts enabled, which would indeed be bad. Except that all > > of the stack traces that it shows have these locks held within the > > scheduling-clock interrupt handler. Now with the "rcu: Don't invoke > > try_invoke_on_locked_down_task() with irqs disabled" but without the > > "sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled" > > commit, I understand why. With both, I don't see how this happens. > > I'm at a loss, but happy to keep bisecting and trying patches. I'm also > considering: > > Is it the compiler? Probably not, I tried 2 versions of GCC. > > Can we trust lockdep to precisely know IRQ state? I know there's > been some recent work around this, but hopefully we're not > affected here? > > Is QEMU buggy? > > > At this point, I am reduced to adding lockdep_assert_irqs_disabled() > > calls at various points in that code, as shown in the patch below. > > > > At this point, I would guess that your first priority would be the > > initial bug rather than this following issue, but you never know, this > > might well help diagnose the initial bug. > > I don't mind either way. I'm worried deadlocking the whole system might > be worse. Here is another set of lockdep_assert_irqs_disabled() calls on the off-chance that they actually find something. Thanx, Paul ------------------------------------------------------------------------ commit bcca5277df3f24db15e15ccc8b05ecf346d05169 Author: Paul E. McKenney Date: Thu Nov 19 13:30:33 2020 -0800 rcu: Add lockdep_assert_irqs_disabled() to raw_spin_unlock_rcu_node() macros This commit adds a lockdep_assert_irqs_disabled() call to the helper macros that release the rcu_node structure's ->lock, namely to raw_spin_unlock_rcu_node(), raw_spin_unlock_irq_rcu_node() and raw_spin_unlock_irqrestore_rcu_node(). The point of this is to help track down a situation where lockdep appears to be insisting that interrupts are enabled while holding an rcu_node structure's ->lock. Link: https://lore.kernel.org/lkml/20201111133813.GA81547@elver.google.com/ Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 59ef1ae..bf0827d 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -378,7 +378,11 @@ do { \ smp_mb__after_unlock_lock(); \ } while (0) -#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock)) +#define raw_spin_unlock_rcu_node(p) \ +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irq_rcu_node(p) \ do { \ @@ -387,7 +391,10 @@ do { \ } while (0) #define raw_spin_unlock_irq_rcu_node(p) \ - raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irqsave_rcu_node(p, flags) \ do { \ @@ -396,7 +403,10 @@ do { \ } while (0) #define raw_spin_unlock_irqrestore_rcu_node(p, flags) \ - raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags); \ +} while (0) #define raw_spin_trylock_rcu_node(p) \ ({ \ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel