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Fri, 06 Sep 2019 12:51:39 -0700 (PDT) Received: from localhost ([121.137.63.184]) by smtp.gmail.com with ESMTPSA id q4sm7413899pfh.115.2019.09.06.12.51.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Sep 2019 12:51:38 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Sat, 7 Sep 2019 04:51:35 +0900 To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Qian Cai , davem@davemloft.net, Eric Dumazet , Sergey Senozhatsky , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure Message-ID: <20190906195135.GA69785@tigerII.localdomain> References: <20190904061501.GB3838@dhcp22.suse.cz> <20190904064144.GA5487@jagdpanzerIV> <20190904065455.GE3838@dhcp22.suse.cz> <20190904071911.GB11968@jagdpanzerIV> <20190904074312.GA25744@jagdpanzerIV> <1567599263.5576.72.camel@lca.pw> <20190904144850.GA8296@tigerII.localdomain> <1567629737.5576.87.camel@lca.pw> <20190905113208.GA521@jagdpanzerIV> <20190906145533.4uw43a5pvsawmdov@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190906145533.4uw43a5pvsawmdov@pathway.suse.cz> User-Agent: Mutt/1.12.1 (2019-06-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On (09/06/19 16:55), Petr Mladek wrote: > > I think we can queue significantly much less irq_work-s from printk(). > > > > Petr, Steven, what do you think? > > > > Something like this. Call wake_up_interruptible(), switch to > > wake_up_klogd() only when called from sched code. > > Replacing irq_work_queue() with wake_up_interruptible() looks > dangerous to me. > > As a result, all "normal" printk() calls from the scheduler > code will deadlock. There is almost always a userspace > logger registered. I don't see why all printk()-s should deadlock. A "normal" printk() call will deadlock only when scheduler calls "normal" printk() under rq or pi locks. But this is illegal anyway, because console_sem up() calls wake_up_process() - the same function wake_up_interruptible() calls. IOW "normal" printk() calls from scheduler end up in scheduler, via console_sem->sched chain. We already execute wake_up_process()->try_to_wake_up() in printk(), even when a non-LOGLEVEL_SCHED printk() comes from scheduler. What am I missing something? -ss