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[94.245.46.49]) by smtp.gmail.com with ESMTPSA id m1sm1224034lfa.22.2020.07.16.07.47.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Jul 2020 07:47:30 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 16 Jul 2020 16:47:28 +0200 To: Sebastian Andrzej Siewior Cc: Uladzislau Rezki , Joel Fernandes , LKML , RCU , linux-mm , "Paul E . McKenney" , Andrew Morton , "Theodore Y . Ts'o" , Matthew Wilcox , Oleksiy Avramchenko Subject: Re: [PATCH 1/1] rcu/tree: Drop the lock before entering to page allocator Message-ID: <20200716144728.GA31046@pc636> References: <20200715183537.4010-1-urezki@gmail.com> <20200715185628.7b4k3o5efp4gnbla@linutronix.de> <20200716091913.GA28595@pc636> <20200716142537.ecp4icsq7kg6qhdx@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200716142537.ecp4icsq7kg6qhdx@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: C56451804B660 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 16, 2020 at 04:25:37PM +0200, Sebastian Andrzej Siewior wrote: > On 2020-07-16 11:19:13 [+0200], Uladzislau Rezki wrote: > > Sebastian, could you please confirm that if that patch that is in > > question fixes it? > > > > It would be appreciated! > > So that preempt disable should in terms any warnings. However I don't > think that it is strictly needed and from scheduling point of view you > forbid a CPU migration which might be good otherwise. > Please elaborate your point regarding "i do not think it is strictly needed". Actually i can rework the patch to remove even such preempt_enable/disable to stay on the same CPU, but i do not see the point of doing it. Do you see the point? As for scheduling point of view. Well, there are many places when there is a demand in memory or pages from atomic context. Also, getting a page is not considered as a hot path in the kfree_rcu(). > > Also if interrupts and everything is enabled then someone else might > invoke kfree_rcu() from BH context for instance. > And what? What is a problem here, please elaborate if you see any issues. -- Vlad Rezki