Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757077AbdHYOsF convert rfc822-to-8bit (ORCPT ); Fri, 25 Aug 2017 10:48:05 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:41900 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756738AbdHYOsE (ORCPT ); Fri, 25 Aug 2017 10:48:04 -0400 Date: Fri, 25 Aug 2017 16:47:55 +0200 From: Sebastian Andrzej Siewior To: Borislav Petkov , Byungchul Park Cc: Thomas Gleixner , Peter Zijlstra , lkml Subject: Re: WARNING: possible circular locking dependency detected Message-ID: <20170825144755.ms2h2j2xe6gznnqi@linutronix.de> References: <20170825100304.5cwrlrfwi7f3zcld@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <20170825100304.5cwrlrfwi7f3zcld@pd.tnic> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2123 Lines: 60 On 2017-08-25 12:03:04 [+0200], Borislav Petkov wrote: > ====================================================== > WARNING: possible circular locking dependency detected > 4.13.0-rc6+ #1 Not tainted > ------------------------------------------------------ While looking at this, I stumbled upon another one also enabled by "completion annotation" in the TIP: | ====================================================== | WARNING: possible circular locking dependency detected | 4.13.0-rc6-00758-gd80d4177391f-dirty #112 Not tainted | ------------------------------------------------------ | cpu-off.sh/426 is trying to acquire lock: | ((complete)&st->done){+.+.}, at: [] takedown_cpu+0x84/0xf0 | | but task is already holding lock: | (sparse_irq_lock){+.+.}, at: [] irq_lock_sparse+0x12/0x20 | | which lock already depends on the new lock. | | the existing dependency chain (in reverse order) is: | | -> #1 (sparse_irq_lock){+.+.}: | __mutex_lock+0x88/0x9a0 | mutex_lock_nested+0x16/0x20 | irq_lock_sparse+0x12/0x20 | irq_affinity_online_cpu+0x13/0xd0 | cpuhp_invoke_callback+0x4a/0x130 | | -> #0 ((complete)&st->done){+.+.}: | check_prev_add+0x351/0x700 | __lock_acquire+0x114a/0x1220 | lock_acquire+0x47/0x70 | wait_for_completion+0x5c/0x180 | takedown_cpu+0x84/0xf0 | cpuhp_invoke_callback+0x4a/0x130 | cpuhp_down_callbacks+0x3d/0x80 … | | other info that might help us debug this: | | Possible unsafe locking scenario: | CPU0 CPU1 | ---- ---- | lock(sparse_irq_lock); | lock((complete)&st->done); | lock(sparse_irq_lock); | lock((complete)&st->done); | | *** DEADLOCK *** We hold the sparse_irq_lock lock while waiting for the completion in the CPU-down case and in the CPU-up case we acquire the sparse_irq_lock lock while the other CPU is waiting for the completion. This is not an issue if my interpretation of lockdep here is correct. How do we annotate this? Sebastian