linux-kernel - Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread

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Message-ID: <20170407072143.GB11792@amd>
Date:   Fri, 7 Apr 2017 09:21:43 +0200
From:   Pavel Machek <pavel@....cz>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Len Brown <len.brown@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCHv2 2/8] printk: introduce printing kernel thread

Hi!

> spin_dump() and trigger_all_cpu_backtrace() result in a bunch of
> additional printk()-s so CPU0 has even more job to do in console_unlock(),
> while it still holds the contended spin_lock. and so on; there are
> many other examples.
> 
> so should we declare a "we can spend only 2 seconds in direct printk()
> and then must offload printing" rule? I don't think it's much better
> than a simpler "we always offload, as long as we think it's safe".

I believe we should do the 2 seconds rule. It allows us to print "some
messages delayed" message, so at least whoever is trying to debug the
crash will have the hints that he needs to look at the printk system.

"we always offload, as long as we think it's safe" rule does not
really work, as printk() can not detect if it is safe or not.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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