From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f175.google.com (mail-ie0-f175.google.com [209.85.223.175]) by kanga.kvack.org (Postfix) with ESMTP id EAE156B027B for ; Tue, 14 Jul 2015 19:48:26 -0400 (EDT) Received: by iebmu5 with SMTP id mu5so22388823ieb.1 for ; Tue, 14 Jul 2015 16:48:26 -0700 (PDT) Received: from mail-ig0-x22a.google.com (mail-ig0-x22a.google.com. [2607:f8b0:4001:c05::22a]) by mx.google.com with ESMTPS id b199si2104030ioe.42.2015.07.14.16.48.26 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Jul 2015 16:48:26 -0700 (PDT) Received: by igcqs7 with SMTP id qs7so94388382igc.0 for ; Tue, 14 Jul 2015 16:48:26 -0700 (PDT) Date: Tue, 14 Jul 2015 16:48:24 -0700 (PDT) From: David Rientjes Subject: Re: cpu_hotplug vs oom_notify_list: possible circular locking dependency detected In-Reply-To: <20150714232943.GW3717@linux.vnet.ibm.com> Message-ID: References: <20150712105634.GA11708@marcin-Inspiron-7720> <20150714232943.GW3717@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="397176738-422283606-1436917705=:16182" Sender: owner-linux-mm@kvack.org List-ID: To: "Paul E. McKenney" Cc: =?UTF-8?Q?Marcin_=C5=9Alusarz?= , Tejun Heo , LKML , linux-mm@kvack.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --397176738-422283606-1436917705=:16182 Content-Type: TEXT/PLAIN; charset=UTF-8 Content-Transfer-Encoding: 8BIT On Tue, 14 Jul 2015, Paul E. McKenney wrote: > commit a1992f2f3b8e174d740a8f764d0d51344bed2eed > Author: Paul E. McKenney > Date: Tue Jul 14 16:24:14 2015 -0700 > > rcu: Don't disable CPU hotplug during OOM notifiers > > RCU's rcu_oom_notify() disables CPU hotplug in order to stabilize the > list of online CPUs, which it traverses. However, this is completely > pointless because smp_call_function_single() will quietly fail if invoked > on an offline CPU. Because the count of requests is incremented in the > rcu_oom_notify_cpu() function that is remotely invoked, everything works > nicely even in the face of concurrent CPU-hotplug operations. > > Furthermore, in recent kernels, invoking get_online_cpus() from an OOM > notifier can result in deadlock. This commit therefore removes the > call to get_online_cpus() and put_online_cpus() from rcu_oom_notify(). > > Reported-by: Marcin A?lusarz > Reported-by: David Rientjes > Signed-off-by: Paul E. McKenney Acked-by: David Rientjes --397176738-422283606-1436917705=:16182-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org