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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id 29sm7794713qkp.86.2019.09.04.05.14.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 04 Sep 2019 05:14:24 -0700 (PDT) Message-ID: <1567599263.5576.72.camel@lca.pw> Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure From: Qian Cai To: Sergey Senozhatsky , Michal Hocko Cc: Eric Dumazet , davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Petr Mladek , Sergey Senozhatsky , Steven Rostedt Date: Wed, 04 Sep 2019 08:14:23 -0400 In-Reply-To: <20190904074312.GA25744@jagdpanzerIV> References: <1567178728.5576.32.camel@lca.pw> <229ebc3b-1c7e-474f-36f9-0fa603b889fb@gmail.com> <20190903132231.GC18939@dhcp22.suse.cz> <1567525342.5576.60.camel@lca.pw> <20190903185305.GA14028@dhcp22.suse.cz> <1567546948.5576.68.camel@lca.pw> <20190904061501.GB3838@dhcp22.suse.cz> <20190904064144.GA5487@jagdpanzerIV> <20190904065455.GE3838@dhcp22.suse.cz> <20190904071911.GB11968@jagdpanzerIV> <20190904074312.GA25744@jagdpanzerIV> 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: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2019-09-04 at 16:43 +0900, Sergey Senozhatsky wrote: > On (09/04/19 16:19), Sergey Senozhatsky wrote: > > Hmm. I need to look at this more... wake_up_klogd() queues work only once > > on particular CPU: irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); > > > > bool irq_work_queue() > > { > > /* Only queue if not already pending */ > > if (!irq_work_claim(work)) > > return false; > > > > __irq_work_queue_local(work); > > } > > Plus one more check - waitqueue_active(&log_wait). printk() adds > pending irq_work only if there is a user-space process sleeping on > log_wait and irq_work is not already scheduled. If the syslog is > active or there is noone to wakeup then we don't queue irq_work. Another possibility for this potential livelock is that those printk() from warn_alloc(), dump_stack() and show_mem() increase the time it needs to process build_skb() allocation failures significantly under memory pressure. As the result, ksoftirqd() could be rescheduled during that time via a different CPU (this is a large x86 NUMA system anyway), [83605.577256][   C31]  run_ksoftirqd+0x1f/0x40 [83605.577256][   C31]  smpboot_thread_fn+0x255/0x440 [83605.577256][   C31]  kthread+0x1df/0x200 [83605.577256][   C31]  ret_from_fork+0x35/0x40 In addition, those printk() will deal with console drivers or even a networking console, so it is probably not unusual that it could call irq_exit()- >__do_softirq() at one point and then this livelock.