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Mon, 23 Sep 2019 18:28:37 -0700 (PDT) Date: Tue, 24 Sep 2019 10:28:34 +0900 From: Sergey Senozhatsky To: Petr Mladek Subject: Re: printk() + memory offline deadlock (WAS Re: page_alloc.shuffle=1 + CONFIG_PROVE_LOCKING=y = arm64 hang) Message-ID: <20190924012834.GC3864@jagdpanzerIV> References: <1567717680.5576.104.camel@lca.pw> <1568128954.5576.129.camel@lca.pw> <20190911011008.GA4420@jagdpanzerIV> <1568289941.5576.140.camel@lca.pw> <20190916104239.124fc2e5@gandalf.local.home> <1568817579.5576.172.camel@lca.pw> <20190918155059.GA158834@tigerII.localdomain> <1568823006.5576.178.camel@lca.pw> <20190923102100.GA1171@jagdpanzerIV> <20190923125851.cykw55jpqwlerjrz@pathway.suse.cz> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190923125851.cykw55jpqwlerjrz@pathway.suse.cz> User-Agent: Mutt/1.12.2 (2019-09-21) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190923_182839_356883_897A2DC5 X-CRM114-Status: GOOD ( 13.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Theodore Ts'o , Sergey Senozhatsky , Arnd Bergmann , linux-mm@kvack.org, Peter Zijlstra , Catalin Marinas , linux-kernel@vger.kernel.org, Steven Rostedt , Sergey Senozhatsky , Qian Cai , Greg Kroah-Hartman , Waiman Long , Dan Williams , Will Deacon , Thomas Gleixner , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On (09/23/19 14:58), Petr Mladek wrote: > > If I understand it correctly then this is the re-appearing problem. > The only systematic solution with the current approach is to > take port->lock in printk_safe/printk_deferred context. It probably is. We have a number of reverse paths. TTY invokes MM under port->lock, UART invokes TTY under port->lock, MM invokes UART under zone->lock, UART invokes sched under port->lock, shced invokes UART, UART invokes UART under port->lock (!), and so on. > But this is a massive change that almost nobody wants. Instead, > we want the changes that were discussed on Plumbers. > > Now, the question is what to do with existing kernels. There were > several lockdep reports. And I am a bit lost. Did anyone seen > real deadlocks or just the lockdep reports? I think so. Qian Cai mentioned "a hang" in one of his reports (was it unseeded random()?). I'll send a formal patch maybe, since there were no objections. > To be clear. I would feel more comfortable when there are no > deadlocks. But I also do not want to invest too much time > into old kernels. All these problems were there for ages. > We could finally see them because lockdep was enabled in printk() > thanks to printk_safe. True. Everyone was so much happier when printk() used to do lockdep_off(); call_console_drivers(); lockdep_on(); Now we can have lockdep and RCU checks enabled, yet somehow printk_safe is still "a terrible thing" :) -ss _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel