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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7A15C433FE for ; Mon, 7 Nov 2022 17:13:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232331AbiKGRM7 (ORCPT ); Mon, 7 Nov 2022 12:12:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231302AbiKGRM5 (ORCPT ); Mon, 7 Nov 2022 12:12:57 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB4CF1FFAE for ; Mon, 7 Nov 2022 09:12:56 -0800 (PST) Date: Mon, 7 Nov 2022 18:12:53 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1667841175; 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=oJ4z5vz/SZp2P2GdrW8ObedoYrFcfWUErVhcj97ybgI=; b=yjk50vTfE5/rJGMG1gJOiGEscLxL36PbMnp/bSMcAhLwR3QJvKlpnLbon/PsBj/LVi24bZ NH6CYp+LqzB/OBz41Cnp97nQ2/a38wwAwMPSd8o+rakBVIklK+3czkfADcaX7AMVgL8ACR qd2vMdjo7l/jcM9zhnVLA34avECggqYjhLvVFdjy3Cp/EJzg1BXL/wADhBJjJK1v4YRAy+ 2DyHsDz3FHgqRVbi6XkkE7fGJ4GI2ptY44UmMnVRAyyN6733z/LZD5Wf/7yAPV5CY8d/cn 6T9J82BKatf17xD6pO+3rIR0j57YGL1WE3gtgVICkbAX3kv0e+jBjpjfffescw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1667841175; 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=oJ4z5vz/SZp2P2GdrW8ObedoYrFcfWUErVhcj97ybgI=; b=QxdSP3Y5XqS+eLr2dyoScoikpLyN7AeKu/sc8mwzLp7Clyhdz1iY+JtngjxTI9fry2xzJ2 6Jny/fqZ6TNe5PDg== From: Sebastian Andrzej Siewior To: Jan Kara Cc: LKML , Thomas Gleixner , Steven Rostedt , Mel Gorman , Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Catalin Marinas Subject: Re: Crash with PREEMPT_RT on aarch64 machine Message-ID: References: <20221103115444.m2rjglbkubydidts@quack3> <20221107135636.biouna36osqc4rik@quack3> <20221107163016.cnzhknmdnhajfxdh@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221107163016.cnzhknmdnhajfxdh@quack3> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-11-07 17:30:16 [+0100], Jan Kara wrote: > On Mon 07-11-22 16:10:34, Sebastian Andrzej Siewior wrote: > > + locking, arm64 > > > > On 2022-11-07 14:56:36 [+0100], Jan Kara wrote: > > > > spinlock_t and raw_spinlock_t differ slightly in terms of locking. > > > > rt_spin_lock() has the fast path via try_cmpxchg_acquire(). If you > > > > enable CONFIG_DEBUG_RT_MUTEXES then you would force the slow path which > > > > always acquires the rt_mutex_base::wait_lock (which is a raw_spinlock_t) > > > > while the actual lock is modified via cmpxchg. > > > > > > So I've tried enabling CONFIG_DEBUG_RT_MUTEXES and indeed the corruption > > > stops happening as well. So do you suspect some bug in the CPU itself? > > > > If it is only enabling CONFIG_DEBUG_RT_MUTEXES (and not whole lockdep) > > then it looks very suspicious. > > Just to confirm, CONFIG_DEBUG_RT_MUTEXES is the only thing I've enabled and > the list corruption disappeared. I don't know if this works but: if you tell task_struct_cachep to be created with SLAB_CACHE_DMA32 then the pointer should only have the lower 32bit set. With this could make rt_mutex_base::owner an atomic_t type. You could then replace try_cmpxchg_acquire() with atomic_try_cmpxchg_acquire() and do the 32bit cmpxchg. You would then need set the const upper 32bit of the pointer while returning the pointer. I have no idea how much sense it makes but you would avoid the 64bit cmpxchg making those two a little more alike :) > Honza > Sebastian