linux-kernel - Re: [PATCH] kernel/watchdog: flush all printk nmi buffers when hardlockup detected

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200212011551.GA13208@google.com>
Date:   Wed, 12 Feb 2020 10:15:51 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.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 (20/02/10 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?

	-ss