linux-kernel - Re: [PATCH] printk: inject caller information into the body of message

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Message-ID: <802130a3-b8c1-3973-933b-d6dc5ff2930d@i-love.sakura.ne.jp>
Date:   Fri, 28 Sep 2018 20:21:58 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        kbuild test robot <fengguang.wu@...el.com>,
        syzkaller <syzkaller@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: inject caller information into the body of
 message

On 2018/09/28 17:56, Sergey Senozhatsky wrote:
> The good thing about cont buffer is that we flush it on panic. E.g.
> core/arch early boot stage can do:
> 
> 	pr_cont("going to call early_init_foo()...");
> 	early_init_foo();
> 	pr_cont("OK\n");
> 

Is printing

  going to call early_init_foo()...OK

in one line so critically important? If caller information is prefixed,
we would no longer need to support KERN_CONT. That is, we could do

  printk("going to call early_init_foo()...\n");
  early_init_foo();
  printk("OK\n");

and get output like below.

  T0: going to call early_init_foo()...
  T0: OK

Even if "going to call early_init_foo()..." part became too long,

  T0: going to call
  T0: early_init_foo()...
  T0: OK

will not be so bad.

> should early_init_foo() panic the system we will have
> "going to call early_init_foo()" on the serial console. This can
> be addressed if you'd iterate printk_buffers[] in flush_on_panic().

Yes, flush on panic() would also be possible.



> Tetsuo, do you still want to have a fixed size array of printk buffers?

For my intended users where printk() is used for reporting errors (e.g.
stack backtrace, GFP_ATOMIC memory allocation failure, lockdep splat),
being prepared for already tight stack is preferable.

> 
> What do others think?

Yes, I want to hear from others.