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[209.132.180.67]) by mx.google.com with ESMTP id d5si2651854edq.60.2019.10.10.00.58.48; Thu, 10 Oct 2019 00:59:11 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733101AbfJJH6A (ORCPT + 99 others); Thu, 10 Oct 2019 03:58:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:35234 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1733062AbfJJH57 (ORCPT ); Thu, 10 Oct 2019 03:57:59 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 73269B1B8; Thu, 10 Oct 2019 07:57:57 +0000 (UTC) Date: Thu, 10 Oct 2019 09:57:56 +0200 From: Petr Mladek To: Qian Cai Cc: Christian Borntraeger , Heiko Carstens , sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, Michal Hocko , linux-mm@kvack.org, john.ogness@linutronix.de, akpm@linux-foundation.org, Vasily Gorbik , PeterOberparleiter , david@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191010075756.nyix7l32ai6fylzn@pathway.suse.cz> References: <20191008183525.GQ6681@dhcp22.suse.cz> <1570561573.5576.307.camel@lca.pw> <20191008191728.GS6681@dhcp22.suse.cz> <1570563324.5576.309.camel@lca.pw> <20191009114903.aa6j6sa56z2cssom@pathway.suse.cz> <1570626402.5937.1.camel@lca.pw> <20191009132746.GA6681@dhcp22.suse.cz> <1570628593.5937.3.camel@lca.pw> <20191009142438.yx74ukfqwy2hr4fz@pathway.suse.cz> <1570632374.5937.8.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1570632374.5937.8.camel@lca.pw> User-Agent: NeoMutt/20170912 (1.9.0) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 2019-10-09 10:46:14, Qian Cai wrote: > On Wed, 2019-10-09 at 16:24 +0200, Petr Mladek wrote: > > On Wed 2019-10-09 09:43:13, Qian Cai wrote: > > > On Wed, 2019-10-09 at 15:27 +0200, Michal Hocko wrote: > > > > On Wed 09-10-19 09:06:42, Qian Cai wrote: > > > > [...] > > > > > https://lore.kernel.org/linux-mm/1570460350.5576.290.camel@lca.pw/ > > > > > > > > > > [??297.425964] -> #1 (&port_lock_key){-.-.}: > > > > > [??297.425967]????????__lock_acquire+0x5b3/0xb40 > > > > > [??297.425967]????????lock_acquire+0x126/0x280 > > > > > [??297.425968]????????_raw_spin_lock_irqsave+0x3a/0x50 > > > > > [??297.425969]????????serial8250_console_write+0x3e4/0x450 > > > > > [??297.425970]????????univ8250_console_write+0x4b/0x60 > > > > > [??297.425970]????????console_unlock+0x501/0x750 > > > > > [??297.425971]????????vprintk_emit+0x10d/0x340 > > > > > [??297.425972]????????vprintk_default+0x1f/0x30 > > > > > [??297.425972]????????vprintk_func+0x44/0xd4 > > > > > [??297.425973]????????printk+0x9f/0xc5 > > > > > [??297.425974]????????register_console+0x39c/0x520 > > > > > [??297.425975]????????univ8250_console_init+0x23/0x2d > > > > > [??297.425975]????????console_init+0x338/0x4cd > > > > > [??297.425976]????????start_kernel+0x534/0x724 > > > > > [??297.425977]????????x86_64_start_reservations+0x24/0x26 > > > > > [??297.425977]????????x86_64_start_kernel+0xf4/0xfb > > > > > [??297.425978]????????secondary_startup_64+0xb6/0xc0 > > > > > > > > > > where?the report again show the early boot call trace for the locking > > > > > dependency, > > > > > > > > > > console_owner --> port_lock_key > > > > > > > > > > but that dependency clearly not only happen in the early boot. > > > > > > > > Can you provide an example of the runtime dependency without any early > > > > boot artifacts? Because this discussion really doens't make much sense > > > > without a clear example of a _real_ lockdep report that is not a false > > > > possitive. All of them so far have been concluded to be false possitive > > > > AFAIU. > > > > > > An obvious one is in the above link. Just replace the trace in #1 above with > > > printk() from anywhere, i.e., just ignore the early boot calls there as they are > > > not important. > > > > > > printk() > > > console_unlock() > > > console_lock_spinning_enable() --> console_owner_lock > > > call_console_drivers() > > > serial8250_console_write() --> port->lock > > > > Please, find the location where this really happens and then suggests > > how the real deadlock could get fixed. So far, we have seen only > > false positives and theoretical scenarios. > > Now the bar is higher again. You are now asking me to actually trigger this > potential deadlock live. I am probably better off buying some lottery tickets > then if I could be that lucky. No, we just do not want to comlicate the code too much just to hide false positives from lockdep. I do not ask you to reproduce the deadlock. I ask you to find a code path where the deadlock might really happen. It seems that you actually found one in the tty code in the other mail. Best Regards, Petr