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Date:   Fri, 28 Sep 2018 18:09:39 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Alexander Potapenko <glider@google.com>,
        Dmitriy Vyukov <dvyukov@google.com>,
        kbuild test robot <fengguang.wu@intel.com>,
        syzkaller <syzkaller@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] printk: inject caller information into the body of
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On (09/24/18 17:11), Tetsuo Handa wrote:
> The reason of using statically preallocated global buffers is that I think
> that it is inconvenient for KERN_CONT users to calculate necessary bytes
> only for avoiding message truncation. The pr_line might be passed to deep
> into the callchain and adjusting buffer size whenever the content's possible
> max length changes is as much painful as changing printk() to accept only
> one "const char *" argument. Even if we guarantee that any context can
> allocate buffer from kernel stack, we cannot guarantee that many concurrent
> printk() won't trigger lockup. Thus, I think that trying to allocate from
> finite static buffers with a fallback to unbuffered printk() upon failure
> is sufficient.

Yes, this makes sense. At the same time we can keep pr_line buffer
in .bss

	static char buffer[1024];
	static DEFINE_PR_LINE_BUF(..., buffer);

just like you have already mentioned. But that's going to require a
case-by-case handling; so a big list of printk buffers is a simpler
option. Fallback, tho, can be painful. On a system with 1024 CPUs can
one have more than 16 concurrent cont printks? If the answer is yes,
then we are looking at the same broken cont output as before.

	-ss