linux-kernel - Re: [PATCH] debugobjects: Move printk out of db lock critical sections

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Message-ID: <20181213051853.GG4860@jagdpanzerIV>
Date:   Thu, 13 Dec 2018 14:18:53 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     Waiman Long <longman@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Arnd Bergmann <arnd@...db.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] debugobjects: Move printk out of db lock critical
 sections

On (12/13/18 04:35), Dmitry Safonov wrote:
> I've tried to review it and found minor issues like missed
> debug_object_is_on_stack() for initializing already active object.
> 
> But than I come to opinion that it's just generally unsafe:
> debug_obj life-time is protected by bucket's spin_lock.
> Check the conditions when free_object() is being called.

I thought about it for a second, but couldn't figure out if this race
was real.

E.g. uart case - if there are two paths which concurrently free and
access debug object, then the same race condition should exist for
the xmit.buf page. debug object's lifespan should be the same as the
lifespan of, ummm, whatever the thing that debug object is attached
to? I'm surely missing something here.

	-ss