linux-kernel - Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

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Date:   Thu, 11 Jan 2018 20:14:27 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     tj@...nel.org
Cc:     rostedt@...dmis.org, pmladek@...e.com,
        sergey.senozhatsky@...il.com, jack@...e.cz,
        akpm@...ux-foundation.org, peterz@...radead.org, rjw@...ysocki.net,
        pavel@....cz, linux-kernel@...r.kernel.org,
        sergey.senozhatsky.work@...il.com
Subject: Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

Tejun Heo wrote:
> On Wed, Jan 10, 2018 at 07:08:30AM +0900, Tetsuo Handa wrote:
> > > * Netconsole tries to send out OOM messages and tries memory
> > >   allocation which fails which then prints allocation failed messages.
> > >   Because this happens while already printing, it just queues the
> > >   messages to the buffer.  This repeats.
> > 
> > What? Does netconsole need to allocate memory when sending? I assume it does not.
> 
> A lot of network drivers do, unfortunatley.
> 

Excuse me, but can you show me an example of such traces?

Any path which are called from printk() must not (directly or indirectly)
depend on __GFP_DIRECT_RECLAIM && !__GFP_NORETRY memory allocation.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/mm/page_alloc.c?id=e746bf730a76fe53b82c9e6b6da72d58e9ae3565
If it depends on such memory allocation, it can cause OOM lockup.