linux-kernel - Re: [RFC][PATCH 6/7] printk: use alternative printk buffers

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Message-ID: <20161011073528.GA18875@swordfish>
Date:   Tue, 11 Oct 2016 16:35:28 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Calvin Owens <calvinowens@...com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 6/7] printk: use alternative printk buffers

On (10/10/16 13:17), Petr Mladek wrote:
[..]
> > it may look that lockdep *probably* can report the issues via 'safe' printk,
> > but that's a notably huge behavior breakage -- if lockdep report comes from
> > an about-to-deadlock irq handler, then we won't see anything from that CPU
> > unless there is a panic/nmi panic.
> > 
> > so it probably has to be semi-automatic/semi-manual:
> > - add might_printk() that would acquire/release console sem; or
> >   logbuf_lock (which is probably even better)
> > - find all functions that do printk/WARN in kernel/time and kernel/sched
> > - add might_printk() to those functions (just like might_sleep())
> > - run the kernel
> > - ...
> > - profit
> 
> I like the idea with might_printk(). I hope that it will be acceptable
> for the scheduler/timekeeping people.
> 
> JFYI, I could work on the printk-context handling in lockdep.
> I am just working on a lockdep support in NMI and am getting
> kind of familiar with that code.

sorry, what do you mean by 'printk-context handling in lockdep'?
wouldn't `lockdep + might_printk() + printk_safe' be enough? am I
missing something?

	-ss