From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> To: Steven Rostedt <rostedt@goodmis.org> Cc: Tejun Heo <tj@kernel.org>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@home.goodmis.org, Byungchul Park <byungchul.park@lge.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Date: Thu, 11 Jan 2018 13:58:17 +0900 [thread overview] Message-ID: <20180111045817.GA494@jagdpanzerIV> (raw) In-Reply-To: <20180110130517.6ff91716@vmware.local.home> On (01/10/18 13:05), Steven Rostedt wrote: [..] > My solution takes printk from its current unbounded state, and makes it > fixed bounded. Which means printk() is now a O(1) algorithm. ^^^ O(logbuf) and O(logbuf) > watchdog_thresh is totally possible. and there is nothing super unlucky in having O(logbuf). limiting printk is the right way to go, sure. but you limit it to the wrong thing. limiting it to logbuf is not enough, especially given that logbuf size is configurable via kernel param - it's a moving target. if one wants printk to stop disappointing the watchdog then printk must learn to respect watchdog's threshold. https://marc.info/?l=linux-kernel&m=151444381104068 hence a small fix up --- diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8882a4bf2a9e..4efa7542d84d 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2341,6 +2341,14 @@ void console_unlock(void) printk_safe_enter_irqsave(flags); raw_spin_lock(&logbuf_lock); + + if (log_next_seq - console_seq > 666) { + console_seq = log_next_seq; + raw_spin_unlock(&logbuf_lock); + printk_safe_exit_irqrestore(flags); + panic("you mad bro? this can softlockup your system! let me fix that for you"); + } + if (seen_seq != log_next_seq) { wake_klogd = true; seen_seq = log_next_seq; --- > The solution is simple, everyone at KS agreed with it, there should be > no controversy here. frankly speaking, that's not what I recall ;) [..] > My printk solution is solid, with no risk of regressions of current > printk usages. except that handing off a console_sem to atomic task when there is O(logbuf) > watchdog_thresh is a regression, basically... it is what it is. > If anything, I'll pull theses patches myself, and push them to Linus > directly lovely. -ss
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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> To: Steven Rostedt <rostedt@goodmis.org> Cc: Tejun Heo <tj@kernel.org>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@home.goodmis.org, Byungchul Park <byungchul.park@lge.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Date: Thu, 11 Jan 2018 13:58:17 +0900 [thread overview] Message-ID: <20180111045817.GA494@jagdpanzerIV> (raw) In-Reply-To: <20180110130517.6ff91716@vmware.local.home> On (01/10/18 13:05), Steven Rostedt wrote: [..] > My solution takes printk from its current unbounded state, and makes it > fixed bounded. Which means printk() is now a O(1) algorithm. ^^^ O(logbuf) and O(logbuf) > watchdog_thresh is totally possible. and there is nothing super unlucky in having O(logbuf). limiting printk is the right way to go, sure. but you limit it to the wrong thing. limiting it to logbuf is not enough, especially given that logbuf size is configurable via kernel param - it's a moving target. if one wants printk to stop disappointing the watchdog then printk must learn to respect watchdog's threshold. https://marc.info/?l=linux-kernel&m=151444381104068 hence a small fix up --- diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8882a4bf2a9e..4efa7542d84d 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2341,6 +2341,14 @@ void console_unlock(void) printk_safe_enter_irqsave(flags); raw_spin_lock(&logbuf_lock); + + if (log_next_seq - console_seq > 666) { + console_seq = log_next_seq; + raw_spin_unlock(&logbuf_lock); + printk_safe_exit_irqrestore(flags); + panic("you mad bro? this can softlockup your system! let me fix that for you"); + } + if (seen_seq != log_next_seq) { wake_klogd = true; seen_seq = log_next_seq; --- > The solution is simple, everyone at KS agreed with it, there should be > no controversy here. frankly speaking, that's not what I recall ;) [..] > My printk solution is solid, with no risk of regressions of current > printk usages. except that handing off a console_sem to atomic task when there is O(logbuf) > watchdog_thresh is a regression, basically... it is what it is. > If anything, I'll pull theses patches myself, and push them to Linus > directly lovely. -ss -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2018-01-11 4:58 UTC|newest] Thread overview: 280+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-01-10 13:24 [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 13:24 ` [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 16:50 ` Steven Rostedt 2018-01-10 16:50 ` Steven Rostedt 2018-01-12 16:54 ` Steven Rostedt 2018-01-12 16:54 ` Steven Rostedt 2018-01-12 17:11 ` Steven Rostedt 2018-01-12 17:11 ` Steven Rostedt 2018-01-17 19:13 ` Rasmus Villemoes 2018-01-17 19:13 ` Rasmus Villemoes 2018-01-17 19:33 ` Steven Rostedt 2018-01-17 19:33 ` Steven Rostedt 2018-01-19 9:51 ` Sergey Senozhatsky 2018-01-19 9:51 ` Sergey Senozhatsky 2018-01-18 22:03 ` Pavel Machek 2018-01-18 22:03 ` Pavel Machek 2018-01-19 0:20 ` Steven Rostedt 2018-01-19 0:20 ` Steven Rostedt 2018-01-17 2:19 ` Byungchul Park 2018-01-17 2:19 ` Byungchul Park 2018-01-17 4:54 ` Byungchul Park 2018-01-17 4:54 ` Byungchul Park 2018-01-17 7:34 ` Byungchul Park 2018-01-17 7:34 ` Byungchul Park 2018-01-17 12:04 ` Petr Mladek 2018-01-17 12:04 ` Petr Mladek 2018-01-18 1:53 ` Byungchul Park 2018-01-18 1:53 ` Byungchul Park 2018-01-18 1:57 ` Byungchul Park 2018-01-18 1:57 ` Byungchul Park 2018-01-18 2:19 ` Steven Rostedt 2018-01-18 2:19 ` Steven Rostedt 2018-01-18 4:01 ` Byungchul Park 2018-01-18 4:01 ` Byungchul Park 2018-01-18 15:21 ` Steven Rostedt 2018-01-18 15:21 ` Steven Rostedt 2018-01-19 2:37 ` Byungchul Park 2018-01-19 2:37 ` Byungchul Park 2018-01-19 3:27 ` Steven Rostedt 2018-01-19 3:27 ` Steven Rostedt 2018-01-22 2:31 ` Byungchul Park 2018-01-22 2:31 ` Byungchul Park 2018-01-10 13:24 ` [PATCH v5 2/2] printk: Hide console waiter logic into helpers Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 17:52 ` Steven Rostedt 2018-01-10 17:52 ` Steven Rostedt 2018-01-11 12:03 ` Petr Mladek 2018-01-11 12:03 ` Petr Mladek 2018-01-12 15:37 ` Steven Rostedt 2018-01-12 15:37 ` Steven Rostedt 2018-01-12 16:08 ` Petr Mladek 2018-01-12 16:08 ` Petr Mladek 2018-01-12 16:36 ` Steven Rostedt 2018-01-12 16:36 ` Steven Rostedt 2018-01-15 16:08 ` Petr Mladek 2018-01-15 16:08 ` Petr Mladek 2018-01-16 5:05 ` Sergey Senozhatsky 2018-01-16 5:05 ` Sergey Senozhatsky 2018-01-10 14:05 ` [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Tejun Heo 2018-01-10 14:05 ` Tejun Heo 2018-01-10 16:29 ` Petr Mladek 2018-01-10 16:29 ` Petr Mladek 2018-01-10 17:02 ` Tejun Heo 2018-01-10 17:02 ` Tejun Heo 2018-01-10 18:21 ` Peter Zijlstra 2018-01-10 18:21 ` Peter Zijlstra 2018-01-10 18:30 ` Tejun Heo 2018-01-10 18:30 ` Tejun Heo 2018-01-10 18:41 ` Peter Zijlstra 2018-01-10 18:41 ` Peter Zijlstra 2018-01-10 19:05 ` Tejun Heo 2018-01-10 19:05 ` Tejun Heo 2018-01-11 5:15 ` Sergey Senozhatsky 2018-01-11 5:15 ` Sergey Senozhatsky 2018-01-10 18:22 ` Steven Rostedt 2018-01-10 18:22 ` Steven Rostedt 2018-01-10 18:36 ` Tejun Heo 2018-01-10 18:36 ` Tejun Heo 2018-01-10 18:40 ` Mathieu Desnoyers 2018-01-10 18:40 ` Mathieu Desnoyers 2018-01-11 7:36 ` Sergey Senozhatsky 2018-01-11 7:36 ` Sergey Senozhatsky 2018-01-11 11:24 ` Petr Mladek 2018-01-11 11:24 ` Petr Mladek 2018-01-11 13:19 ` Sergey Senozhatsky 2018-01-11 13:19 ` Sergey Senozhatsky 2018-01-24 9:36 ` Peter Zijlstra 2018-01-24 9:36 ` Peter Zijlstra 2018-01-24 18:46 ` Tejun Heo 2018-01-24 18:46 ` Tejun Heo 2018-05-09 8:58 ` Sergey Senozhatsky 2018-05-09 8:58 ` Sergey Senozhatsky 2018-01-10 18:54 ` Steven Rostedt 2018-01-10 18:54 ` Steven Rostedt 2018-01-11 5:10 ` Sergey Senozhatsky 2018-01-11 5:10 ` Sergey Senozhatsky 2018-01-10 18:05 ` Steven Rostedt 2018-01-10 18:05 ` Steven Rostedt 2018-01-10 18:12 ` Tejun Heo 2018-01-10 18:12 ` Tejun Heo 2018-01-10 18:14 ` Tejun Heo 2018-01-10 18:14 ` Tejun Heo 2018-01-10 18:45 ` Steven Rostedt 2018-01-10 18:45 ` Steven Rostedt 2018-01-10 18:41 ` Steven Rostedt 2018-01-10 18:41 ` Steven Rostedt 2018-01-10 18:57 ` Tejun Heo 2018-01-10 18:57 ` Tejun Heo 2018-01-10 19:17 ` Steven Rostedt 2018-01-10 19:17 ` Steven Rostedt 2018-01-10 19:34 ` Tejun Heo 2018-01-10 19:34 ` Tejun Heo 2018-01-10 19:44 ` Steven Rostedt 2018-01-10 19:44 ` Steven Rostedt 2018-01-10 22:44 ` Tejun Heo 2018-01-10 22:44 ` Tejun Heo 2018-01-11 5:35 ` Sergey Senozhatsky 2018-01-11 5:35 ` Sergey Senozhatsky 2018-01-11 4:58 ` Sergey Senozhatsky [this message] 2018-01-11 4:58 ` Sergey Senozhatsky 2018-01-11 9:34 ` Petr Mladek 2018-01-11 9:34 ` Petr Mladek 2018-01-11 10:38 ` Sergey Senozhatsky 2018-01-11 10:38 ` Sergey Senozhatsky 2018-01-11 11:50 ` Petr Mladek 2018-01-11 11:50 ` Petr Mladek 2018-01-11 16:29 ` Steven Rostedt 2018-01-11 16:29 ` Steven Rostedt 2018-01-12 1:30 ` Steven Rostedt 2018-01-12 1:30 ` Steven Rostedt 2018-01-12 2:55 ` Steven Rostedt 2018-01-12 2:55 ` Steven Rostedt 2018-01-12 4:20 ` Steven Rostedt 2018-01-12 4:20 ` Steven Rostedt 2018-01-16 19:44 ` Tejun Heo 2018-01-16 19:44 ` Tejun Heo 2018-01-17 9:12 ` Petr Mladek 2018-01-17 9:12 ` Petr Mladek 2018-01-17 15:15 ` Tejun Heo 2018-01-17 15:15 ` Tejun Heo 2018-01-17 17:12 ` Steven Rostedt 2018-01-17 17:12 ` Steven Rostedt 2018-01-17 18:42 ` Steven Rostedt 2018-01-17 18:42 ` Steven Rostedt 2018-01-19 18:20 ` Steven Rostedt 2018-01-19 18:20 ` Steven Rostedt 2018-01-20 7:14 ` Sergey Senozhatsky 2018-01-20 7:14 ` Sergey Senozhatsky 2018-01-20 15:49 ` Steven Rostedt 2018-01-20 15:49 ` Steven Rostedt 2018-01-21 14:15 ` Sergey Senozhatsky 2018-01-21 14:15 ` Sergey Senozhatsky 2018-01-21 21:04 ` Steven Rostedt 2018-01-21 21:04 ` Steven Rostedt 2018-01-22 8:56 ` Sergey Senozhatsky 2018-01-22 8:56 ` Sergey Senozhatsky 2018-01-22 10:28 ` Sergey Senozhatsky 2018-01-22 10:28 ` Sergey Senozhatsky 2018-01-22 10:36 ` Sergey Senozhatsky 2018-01-22 10:36 ` Sergey Senozhatsky 2018-01-23 6:40 ` Sergey Senozhatsky 2018-01-23 6:40 ` Sergey Senozhatsky 2018-01-23 7:05 ` Sergey Senozhatsky 2018-01-23 7:05 ` Sergey Senozhatsky 2018-01-23 7:31 ` Sergey Senozhatsky 2018-01-23 7:31 ` Sergey Senozhatsky 2018-01-23 14:56 ` Steven Rostedt 2018-01-23 14:56 ` Steven Rostedt 2018-01-23 15:21 ` Sergey Senozhatsky 2018-01-23 15:21 ` Sergey Senozhatsky 2018-01-23 15:41 ` Steven Rostedt 2018-01-23 15:41 ` Steven Rostedt 2018-01-23 15:43 ` Tejun Heo 2018-01-23 15:43 ` Tejun Heo 2018-01-23 16:12 ` Sergey Senozhatsky 2018-01-23 16:12 ` Sergey Senozhatsky 2018-01-23 16:13 ` Steven Rostedt 2018-01-23 16:13 ` Steven Rostedt 2018-01-23 17:21 ` Tejun Heo 2018-01-23 17:21 ` Tejun Heo 2018-04-23 5:35 ` Sergey Senozhatsky 2018-04-23 5:35 ` Sergey Senozhatsky 2018-01-23 16:01 ` Sergey Senozhatsky 2018-01-23 16:01 ` Sergey Senozhatsky 2018-01-23 16:24 ` Steven Rostedt 2018-01-23 16:24 ` Steven Rostedt 2018-01-24 2:11 ` Sergey Senozhatsky 2018-01-24 2:11 ` Sergey Senozhatsky 2018-01-24 2:52 ` Steven Rostedt 2018-01-24 2:52 ` Steven Rostedt 2018-01-24 4:44 ` Sergey Senozhatsky 2018-01-24 4:44 ` Sergey Senozhatsky 2018-01-23 17:22 ` Tejun Heo 2018-01-23 17:22 ` Tejun Heo 2018-01-20 12:19 ` Tejun Heo 2018-01-20 12:19 ` Tejun Heo 2018-01-20 14:51 ` Steven Rostedt 2018-01-20 14:51 ` Steven Rostedt 2018-01-17 20:05 ` Tejun Heo 2018-01-17 20:05 ` Tejun Heo 2018-01-18 5:43 ` Sergey Senozhatsky 2018-01-18 5:43 ` Sergey Senozhatsky 2018-01-18 11:51 ` Petr Mladek 2018-01-18 11:51 ` Petr Mladek 2018-01-18 5:42 ` Sergey Senozhatsky 2018-01-18 5:42 ` Sergey Senozhatsky 2018-01-12 3:12 ` Sergey Senozhatsky 2018-01-12 3:12 ` Sergey Senozhatsky 2018-01-12 2:56 ` Sergey Senozhatsky 2018-01-12 2:56 ` Sergey Senozhatsky 2018-01-12 3:21 ` Steven Rostedt 2018-01-12 3:21 ` Steven Rostedt 2018-01-12 10:05 ` Sergey Senozhatsky 2018-01-12 10:05 ` Sergey Senozhatsky 2018-01-12 12:21 ` Steven Rostedt 2018-01-12 12:21 ` Steven Rostedt 2018-01-12 12:55 ` Petr Mladek 2018-01-12 12:55 ` Petr Mladek 2018-01-13 7:31 ` Sergey Senozhatsky 2018-01-13 7:31 ` Sergey Senozhatsky 2018-01-15 8:51 ` Petr Mladek 2018-01-15 8:51 ` Petr Mladek 2018-01-15 9:48 ` Sergey Senozhatsky 2018-01-15 9:48 ` Sergey Senozhatsky 2018-01-16 5:16 ` Sergey Senozhatsky 2018-01-16 5:16 ` Sergey Senozhatsky 2018-01-16 9:08 ` Petr Mladek 2018-01-16 9:08 ` Petr Mladek 2018-01-15 12:08 ` Steven Rostedt 2018-01-15 12:08 ` Steven Rostedt 2018-01-16 4:51 ` Sergey Senozhatsky 2018-01-16 4:51 ` Sergey Senozhatsky 2018-01-13 7:28 ` Sergey Senozhatsky 2018-01-13 7:28 ` Sergey Senozhatsky 2018-01-15 10:17 ` Petr Mladek 2018-01-15 10:17 ` Petr Mladek 2018-01-15 11:50 ` Petr Mladek 2018-01-15 11:50 ` Petr Mladek 2018-01-16 6:10 ` Sergey Senozhatsky 2018-01-16 6:10 ` Sergey Senozhatsky 2018-01-16 9:36 ` Petr Mladek 2018-01-16 9:36 ` Petr Mladek 2018-01-16 10:10 ` Sergey Senozhatsky 2018-01-16 10:10 ` Sergey Senozhatsky 2018-01-16 16:06 ` Steven Rostedt 2018-01-16 16:06 ` Steven Rostedt 2018-01-16 5:23 ` Sergey Senozhatsky 2018-01-16 5:23 ` Sergey Senozhatsky 2018-01-15 12:06 ` Steven Rostedt 2018-01-15 12:06 ` Steven Rostedt 2018-01-15 14:45 ` Petr Mladek 2018-01-15 14:45 ` Petr Mladek 2018-01-16 2:23 ` Sergey Senozhatsky 2018-01-16 2:23 ` Sergey Senozhatsky 2018-01-16 4:47 ` Sergey Senozhatsky 2018-01-16 4:47 ` Sergey Senozhatsky 2018-01-16 10:19 ` Petr Mladek 2018-01-16 10:19 ` Petr Mladek 2018-01-17 2:24 ` Sergey Senozhatsky 2018-01-17 2:24 ` Sergey Senozhatsky 2018-01-16 15:45 ` Steven Rostedt 2018-01-16 15:45 ` Steven Rostedt 2018-01-17 2:18 ` Sergey Senozhatsky 2018-01-17 2:18 ` Sergey Senozhatsky 2018-01-17 13:04 ` Petr Mladek 2018-01-17 13:04 ` Petr Mladek 2018-01-17 15:24 ` Steven Rostedt 2018-01-17 15:24 ` Steven Rostedt 2018-01-18 4:31 ` Sergey Senozhatsky 2018-01-18 4:31 ` Sergey Senozhatsky 2018-01-18 15:22 ` Steven Rostedt 2018-01-18 15:22 ` Steven Rostedt 2018-01-16 10:13 ` Petr Mladek 2018-01-16 10:13 ` Petr Mladek 2018-01-17 6:29 ` Sergey Senozhatsky 2018-01-17 6:29 ` Sergey Senozhatsky 2018-01-16 1:46 ` Sergey Senozhatsky 2018-01-16 1:46 ` Sergey Senozhatsky
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