From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2 3/3] printk/nmi: Prevent deadlock when accessing the main log buffer in NMI
Date: Thu, 28 Jun 2018 11:41:25 +0200 [thread overview]
Message-ID: <20180628094125.cq5qunckjyxhbovb@pathway.suse.cz> (raw)
In-Reply-To: <20180628022507.GD481@jagdpanzerIV>
On Thu 2018-06-28 11:25:07, Sergey Senozhatsky wrote:
> On (06/27/18 16:20), Petr Mladek wrote:
> > +/*
> > + * Marks a code that might produce many messages in NMI context
> > + * and the risk of losing them is more critical than eventual
> > + * reordering.
> > + *
> > + * It has effect only when called in NMI context. Then printk()
> > + * will try to store the messages into the main logbuf directly
> > + * and use the per-CPU buffers only as a fallback when the lock
> > + * is not available.
> > + */
> > +void printk_nmi_direct_enter(void)
> > +{
> > + if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
> > + this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
> > +}
>
> A side note: This nesting also handles recursive printk-s for us.
>
> NMI:
> printk_nmi_enter
> ftrace_dump
> printk_nmi_direct_enter
> vprintk_func
> spin_lock(logbuf_lock)
> vprintk_store
> vsprintf
> WARN_ON
> vprintk_func
> vprintk_nmi
Uff, it seems that the current design is "good" at lest from some
points of view.
> > __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
> > {
> > + /*
> > + * Try to use the main logbuf even in NMI. But avoid calling console
> > + * drivers that might have their own locks.
> > + */
> > + if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
> > + raw_spin_trylock(&logbuf_lock)) {
> > + int len;
> > +
> > + len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
> > + raw_spin_unlock(&logbuf_lock);
> > + defer_console();
> > + return len;
> > + }
>
> So, maybe, something a bit better than defer_console().
I am not super happy with the name either. But wakeup_console(),
schedule_console(), or queue_console() looked confusing.
Also I thought about poke_console() but I guess that I already suggested
this name in the past and people did not like it.
Feel free to suggest anything.
> Otherwise,
> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Anyway, thanks a lot for review.
Best Regards,
Petr
next prev parent reply other threads:[~2018-06-28 19:04 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-27 14:08 [PATCH v2 0/3] printk: Deadlock in NMI regression Petr Mladek
2018-06-27 14:08 ` [PATCH v2 1/3] printk: Split the code for storing a message into the log buffer Petr Mladek
2018-06-28 2:10 ` Sergey Senozhatsky
2018-06-27 14:08 ` [PATCH v2 2/3] printk: Create helper function to queue deferred console handling Petr Mladek
2018-06-28 2:16 ` Sergey Senozhatsky
2018-06-28 2:19 ` Sergey Senozhatsky
2018-06-27 14:16 ` [PATCH v2 0/3] printk: Deadlock in NMI regression Sergey Senozhatsky
2018-06-27 14:23 ` Sergey Senozhatsky
2018-06-27 14:34 ` Petr Mladek
2018-06-28 9:08 ` Sergey Senozhatsky
2018-06-27 14:20 ` [PATCH v2 3/3] printk/nmi: Prevent deadlock when accessing the main log buffer in NMI Petr Mladek
2018-06-28 2:25 ` Sergey Senozhatsky
2018-06-28 9:41 ` Petr Mladek [this message]
2018-06-29 1:47 ` Sergey Senozhatsky
2018-06-29 7:25 ` Petr Mladek
2018-06-29 10:01 ` Sergey Senozhatsky
2018-06-28 2:39 ` [PATCH v2 0/3] printk: Deadlock in NMI regression Sergey Senozhatsky
2018-06-28 10:54 ` Petr Mladek
2018-06-29 1:52 ` Sergey Senozhatsky
2018-07-09 13:27 ` Petr Mladek
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