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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 D5E91C433FE for ; Thu, 16 Sep 2021 09:25:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD9CF60F8F for ; Thu, 16 Sep 2021 09:25:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235954AbhIPJ0T (ORCPT ); Thu, 16 Sep 2021 05:26:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236126AbhIPJ0F (ORCPT ); Thu, 16 Sep 2021 05:26:05 -0400 Received: from mail-oi1-x233.google.com (mail-oi1-x233.google.com [IPv6:2607:f8b0:4864:20::233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3739C0613C1 for ; Thu, 16 Sep 2021 02:24:45 -0700 (PDT) Received: by mail-oi1-x233.google.com with SMTP id x141so5567110oix.7 for ; Thu, 16 Sep 2021 02:24:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=YJJaNclf3wzSnd6KFncvUtNJPgnZ1G90tgAnEdwOG7Q=; b=SbSTnF6YB4bss2Kwu3Ep7iIEb7Q6CmnnRp4hjIFt/9Pbhj0Q711D/tuvfqU5zB2Kjc AjQSqIobj2DUtSFPEaZpc0U/vym4bSYEkapUidoU/gnKfC0w4vjWy521Fpw8HdYST4D3 IQEYySJdphMWR8Qt2gOgqw395pigN34xQhmSc8LV2lP/9U7QLfqfE8GvbVcvZTd7JrBC 7LrcCviFVgp0ib51iXroH0631blxOqX8+UwkNtj+2SLuWsDo0c5Ogh++or4k/ig36Oz+ WKGkSIqvhC6lRVAvZQsC4fXhokL4iWJEsKMYmBKlDDbyyeoMnBIbigJwQLE3zxDBKCf8 JZ6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=YJJaNclf3wzSnd6KFncvUtNJPgnZ1G90tgAnEdwOG7Q=; b=sVZovaJASCXKCB1dli0eRR11u+7VzUhFUCRc6OExc4Nn6WxZeLkADN1iJGJl86WxPM dDnq0IPwsr3NsZ4oTriZeisiWFmjJh5FLW8B8svjGg95jVcSRBsW2abozGr/Yovv09+J 7HELn9joZ7uxJGmPULdSHgxjH9chANjet+DJs/qpldw1jNuFLjtVY9F5Bvwz2BNWbAkL mKBzk/WX2b7g5861qDfVRrfvh/k6FgxUJzSSiBPUeN5cRUjGCEx+UXdL/rxewqH6g7yc iW30XCvltuR6To1KUyOlAH6IT9b2CS2nKwdkj0KHc2+yWM7C7FdKxQ4rLvUDlmft1f9F zTaw== X-Gm-Message-State: AOAM532cHAoVvsKnKQ8J0/iNvClcJdWWkC9ygcQNagLFnvBlZUELsS7V vsEOQMZqpC0/Iw5MBwPy3QbqykE7dMCGUHQIRPzCuvU+paEyNg== X-Google-Smtp-Source: ABdhPJxi7CXHXatKk6Ent0JGeDYXpkYxaElSOp3Gne6NRfOXLMwCR+A/DisuphBRfpRFcm02SiUwwPboPjwflF/uMLw= X-Received: by 2002:aca:f189:: with SMTP id p131mr8669427oih.128.1631784285005; Thu, 16 Sep 2021 02:24:45 -0700 (PDT) MIME-Version: 1.0 References: <000000000000eaacf005ca975d1a@google.com> <20210831074532.2255-1-hdanton@sina.com> <20210914123726.4219-1-hdanton@sina.com> <87v933b3wf.ffs@tglx> <87mtoeb4hb.ffs@tglx> <87k0jib2wd.ffs@tglx> In-Reply-To: <87k0jib2wd.ffs@tglx> From: Dmitry Vyukov Date: Thu, 16 Sep 2021 11:24:33 +0200 Message-ID: Subject: Re: [syzbot] INFO: rcu detected stall in syscall_exit_to_user_mode To: Thomas Gleixner Cc: Hillf Danton , syzbot , linux-kernel@vger.kernel.org, paulmck@kernel.org, syzkaller-bugs@googlegroups.com, Peter Zijlstra , kasan-dev , Johannes Berg , Kalle Valo , linux-wireless@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 15 Sept 2021 at 11:32, Thomas Gleixner wrote: > > On Wed, Sep 15 2021 at 11:14, Dmitry Vyukov wrote: > > On Wed, 15 Sept 2021 at 10:57, Thomas Gleixner wrote: > >> That made me actually look at that mac80211_hwsim callback again. > >> > >> hrtimer_forward(&data->beacon_timer, hrtimer_get_expires(timer), > >> ns_to_ktime(bcn_int * NSEC_PER_USEC)); > >> > >> So what this does is really wrong because it tries to schedule the timer > >> on the theoretical periodic timeline. Which goes really south once the > >> timer is late or the callback execution took longer than the > >> period. Hypervisors scheduling out a VCPU at the wrong place will do > >> that for you nicely. > > > > Nice! > > > > You mentioned that hrtimer_run_queues() may not return. Does it mean > > that it can just loop executing the same re-armed callback again and > > again? Maybe then the debug check condition should be that > > hrtimer_run_queues() runs the same callback more than N times w/o > > returning? > > Something like that. I've filed https://bugzilla.kernel.org/show_bug.cgi?id=214429 so that it's not lost. Thanks.