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Date: Wed, 12 Feb 2020 12:04:03 +0900 From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, Petr Mladek <pmladek@...e.com>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>, Konstantin Khlebnikov <khlebnikov@...dex-team.ru> Subject: Re: [PATCH] kernel/watchdog: flush all printk nmi buffers when hardlockup detected On (20/02/11 21:49), Steven Rostedt wrote: > On Wed, 12 Feb 2020 10:15:51 +0900 > Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote: > > > On (20/02/10 12:48), Konstantin Khlebnikov wrote: > > > > > > In NMI context printk() could save messages into per-cpu buffers and > > > schedule flush by irq_work when IRQ are unblocked. This means message > > > about hardlockup appears in kernel log only when/if lockup is gone. > > > > > > Comment in irq_work_queue_on() states that remote IPI aren't NMI safe > > > thus printk() cannot schedule flush work to another cpu. > > > > > > This patch adds simple atomic counter of detected hardlockups and > > > flushes all per-cpu printk buffers in context softlockup watchdog > > > at any other cpu when it sees changes of this counter. > > > > Petr, could you remind me, why do we do PRINTK_NMI_DIRECT_CONTEXT_MASK > > only from ftrace? > > Could it be because its from ftrace_dump() which can spit out millions > of lines from NMI context? Oh, yes, ftrace printks a lot. But I sort of forgot why don't we do the same for "regular" NMIs. So NMIs use per-cpu buffers, expect for NMIs which involve ftrace dump. I'm missing something here. -ss
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