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 9F826C433FE for ; Mon, 7 Nov 2022 15:10:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232792AbiKGPKk (ORCPT ); Mon, 7 Nov 2022 10:10:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232598AbiKGPKi (ORCPT ); Mon, 7 Nov 2022 10:10:38 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E77991DA6F for ; Mon, 7 Nov 2022 07:10:37 -0800 (PST) Date: Mon, 7 Nov 2022 16:10:34 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1667833836; 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=dxahy4MUlQGdZAiwUootSdpPQQmTuITFh2KW+Ggp0P4=; b=zZN4uPxRUSJhni6VwYnJbJeRxq5/VSSrOO+7qqhdQVXQLagFpDyfxGfvh4mapMEreFdYLs drBA4t3nwscD8A5FbCL2tNdJVRkM+6SR9nL+poFMPJhbMfunF40EawvdHVflKNJpCfW42Y EQkWeYqZAHNvVsqTq6vlN1KNQ9LMJTeQecGiMRy6UJSqpHF5vOs9Kl0+m/yMojmXZ8drw/ FdJ8T70NNQA1aOf6pxPraG5QglrTM925SX8dArWixKeozV5OGxt0bGJHR92ICU3Ao4BBV8 I8DM2kLVuRxNPvQhUajh8xuwQdOlcWUe7KaE35EdcmyEzMgwZ8mKvxPT24T4aQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1667833836; 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=dxahy4MUlQGdZAiwUootSdpPQQmTuITFh2KW+Ggp0P4=; b=wHFjQXHG5/PTHlPPZ/eqlfZ4qw6X0XP6KRdlCwyZCygmYqoqs4jY8xznt6ew7Zm2PGowBr OJY2UY43JxK74ABg== 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221107135636.biouna36osqc4rik@quack3> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org + 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. CONFIG_DEBUG_RT_MUTEXES enables a few additional checks but the main part is that rt_mutex_cmpxchg_acquire() + rt_mutex_cmpxchg_release() always fail (and so the slowpath under a raw_spinlock_t is done). So if it is really the fast path (rt_mutex_cmpxchg_acquire()) then it somehow smells like the CPU is misbehaving. Could someone from the locking/arm64 department check if the locking in RT-mutex (rtlock_lock()) is correct? rtmutex locking uses try_cmpxchg_acquire(, ptr, ptr) for the fastpath (and try_cmpxchg_release(, ptr, ptr) for unlock). Now looking at it again, I don't see much difference compared to what queued_spin_trylock() does except the latter always operates on 32bit value instead a pointer. > Honza > Sebastian