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Date: Wed, 25 Oct 2017 19:47:04 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: mhocko@...nel.org Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, xiyou.wangcong@...il.com, hannes@...xchg.org, pmladek@...e.com, sergey.senozhatsky@...il.com, yuwang.yuwang@...baba-inc.com Subject: Re: [PATCH] mm,page_alloc: Serialize out_of_memory() and allocation stall messages. Tetsuo Handa wrote: > While warn_alloc() messages are completely unreadable, what we should note are that > > (a) out_of_memory() => oom_kill_process() => dump_header() => show_mem() => printk() > got stuck at console_unlock() despite this is schedulable context. > > ---------- > 2180: for (;;) { > 2181: struct printk_log *msg; > 2182: size_t ext_len = 0; > 2183: size_t len; > 2184: > 2185: printk_safe_enter_irqsave(flags); > 2186: raw_spin_lock(&logbuf_lock); > (...snipped...) > 2228: console_idx = log_next(console_idx); > 2229: console_seq++; > 2230: raw_spin_unlock(&logbuf_lock); > 2231: > 2232: stop_critical_timings(); /* don't trace print latency */ > 2233: call_console_drivers(ext_text, ext_len, text, len); > 2234: start_critical_timings(); > 2235: printk_safe_exit_irqrestore(flags); // console_unlock+0x24e/0x4c0 is here. > 2236: > 2237: if (do_cond_resched) > 2238: cond_resched(); > 2239: } > ---------- It turned out that cond_resched() was not called due to do_cond_resched == 0 due to preemptible() == 0 due to CONFIG_PREEMPT_COUNT=n despite CONFIG_PREEMPT_VOLUNTARY=y, for CONFIG_PREEMPT_VOLUNTARY itself does not select CONFIG_PREEMPT_COUNT. Surprising...
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