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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id c126sm9268342qkd.13.2019.10.08.06.06.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Oct 2019 06:06:31 -0700 (PDT) Message-ID: <1570539989.5576.295.camel@lca.pw> Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() From: Qian Cai To: Michal Hocko Cc: Petr Mladek , 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 Date: Tue, 08 Oct 2019 09:06:29 -0400 In-Reply-To: <20191008123920.GI6681@dhcp22.suse.cz> References: <20191008103907.GE6681@dhcp22.suse.cz> <3836DE34-9DD2-4815-9E1E-CB87D881B9AD@lca.pw> <20191008123920.GI6681@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 14:39 +0200, Michal Hocko wrote: > On Tue 08-10-19 08:00:43, Qian Cai wrote: > > > > > > > On Oct 8, 2019, at 6:39 AM, Michal Hocko wrote: > > > > > > Have you actually triggered any real deadlock? With a zone->lock in > > > place it would be pretty clear with hard lockups detected. > > > > Yes, I did trigger here and there, and those lockdep splats are > > especially useful to figure out why. > > Can you provide a lockdep splat from an actual deadlock please? I am > sorry but your responses tend to be really cryptic and I never know when > you are talking about actual deadlocks and lockdep splats. I have asked > about the former several times never receiving a specific answer. It is very time-consuming to confirm a lockdep splat is 100% matching a deadlock giving that it is not able to reproduce on will yet, so when I did encounter a memory offline deadlock where "echo offline > memory/state" just hang, but there is no hard lockup probably because the hard lockup detector did not work properly for some reasons or it keep trying to acquire a spin lock that only keep the CPU 100%.