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=-5.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 2F822C433EF for ; Wed, 15 Sep 2021 09:32:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13AD5610D1 for ; Wed, 15 Sep 2021 09:32:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232090AbhIOJd0 (ORCPT ); Wed, 15 Sep 2021 05:33:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229785AbhIOJdZ (ORCPT ); Wed, 15 Sep 2021 05:33:25 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B871C061574; Wed, 15 Sep 2021 02:32:06 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1631698323; 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=WbtaLyN7bc/D5y/kWdbb4hJQoxC3BRCKmIuJD4Msv60=; b=PnQrEKGeDM1uKX6dWFrx5doA2OvA8rNZ6xG3vlF/PXtN2qs29zJVCOSJMWfv+7Dcs2TlAk vevuwzcm4Z7UYSJuRsx5kjBLPoKNHn9IfsIe3zQfQDpLM4Nxw98n4aPgyucwmSLTgvnEqa Q5sXSRT9wY8aOBr2FIojQkDfrnvXL1ZXQDauodNubGglqAjfpGwvQKaCLxxODpCkbyuWRl tBZpYUgYR3YTYzXevs9yZuKjyfxFHS5wXgqH4TKiGVtGCBeg7SX+WYcpzrzc0PiLvxXpnc oF3zEduNfoCJ+ikq4Zs5cqT9gJRyBHlP4gcmWGnqgQMXwfH/nS8hvU/d3ABPPw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1631698323; 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=WbtaLyN7bc/D5y/kWdbb4hJQoxC3BRCKmIuJD4Msv60=; b=9jXDKBdeYWN3H5v3Zu/2lVd2wkzPK0jiD1YoUcfY/vX4I3fQ3JIpUMdQbDii/yBJ5UCF0R pbjudhEU5DZnLzCg== To: Dmitry Vyukov 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 Subject: Re: [syzbot] INFO: rcu detected stall in syscall_exit_to_user_mode In-Reply-To: References: <000000000000eaacf005ca975d1a@google.com> <20210831074532.2255-1-hdanton@sina.com> <20210914123726.4219-1-hdanton@sina.com> <87v933b3wf.ffs@tglx> <87mtoeb4hb.ffs@tglx> Date: Wed, 15 Sep 2021 11:32:02 +0200 Message-ID: <87k0jib2wd.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.