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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id v5sm13774071qtk.66.2019.10.08.12.35.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Oct 2019 12:35:26 -0700 (PDT) Message-ID: <1570563324.5576.309.camel@lca.pw> Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() From: Qian Cai To: Michal Hocko Cc: Christian Borntraeger , Petr Mladek , Peter Oberparleiter , akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, john.ogness@linutronix.de, david@redhat.com, linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik Date: Tue, 08 Oct 2019 15:35:24 -0400 In-Reply-To: <20191008191728.GS6681@dhcp22.suse.cz> References: <1570228005-24979-1-git-send-email-cai@lca.pw> <20191007143002.l37bt2lzqtnqjqxu@pathway.suse.cz> <20191007144937.GO2381@dhcp22.suse.cz> <20191008074357.f33f6pbs4cw5majk@pathway.suse.cz> <20191008082752.GB6681@dhcp22.suse.cz> <1570550917.5576.303.camel@lca.pw> <20191008183525.GQ6681@dhcp22.suse.cz> <1570561573.5576.307.camel@lca.pw> <20191008191728.GS6681@dhcp22.suse.cz> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-10-08 at 21:17 +0200, Michal Hocko wrote: > On Tue 08-10-19 15:06:13, Qian Cai wrote: > > On Tue, 2019-10-08 at 20:35 +0200, Michal Hocko wrote: > > [...] > > > I fully agree that this class of lockdep splats are annoying especially > > > when they make the lockdep unusable but please discuss this with lockdep > > > maintainers and try to find some solution rather than go and try to > > > workaround the problem all over the place. If there are places that > > > would result in a cleaner code then go for it but please do not make the > > > code worse just because of a non existent problem flagged by a false > > > positive. > > > > It makes me wonder what make you think it is a false positive for sure. > > Because this is an early init code? Because if it were a real deadlock No, that alone does not prove it is a false positive. There are many places could generate that lock dependency but lockdep will always save the earliest one. > then your system wouldn't boot to get run with the real userspace > (remember there is zone->lock spinlock involved and that means that you > would hit hard lock after few seconds - but I feel I am repeating > myself).