linux-kernel - Re: [PATCHv7 3/8] printk: introduce per-cpu safe

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Message-ID: <20170104133156.GR14894@pathway.suse.cz>
Date:   Wed, 4 Jan 2017 14:31:56 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        Calvin Owens <calvinowens@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCHv7 3/8] printk: introduce per-cpu safe_print seq buffer

On Tue 2016-12-27 23:16:06, Sergey Senozhatsky wrote:
> This patch extends the idea of NMI per-cpu buffers to regions
> that may cause recursive printk() calls and possible deadlocks.
> Namely, printk() can't handle printk calls from schedule code
> or printk() calls from lock debugging code (spin_dump() for instance);
> because those may be called with `sem->lock' already taken or any
> other `critical' locks (p->pi_lock, etc.). An example of deadlock
> can be
> 
> Usage example:
> 
>  printk()
>   printk_safe_enter_irqsave(flags)
>   //
>   //  any printk() call from here will endup in vprintk_safe(),
>   //  that stores messages in a special per-CPU buffer.
>   //
>   printk_safe_exit_irqrestore(flags)
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

I really like the new variants for printk_safe_enter/exit and
different IRQ context.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr