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From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: 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>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [PATCH] printk: inject caller information into the body of message
Date: Fri, 14 Sep 2018 20:50:28 +0900
Message-ID: <20180914115028.GB20572@tigerII.localdomain> (raw)
In-Reply-To: <49d22738-17ad-410a-be0a-d27d76ba9f37@i-love.sakura.ne.jp>

On (09/14/18 19:37), Tetsuo Handa wrote:
> > @@ -20,6 +20,9 @@
> >   * Annotation for a "continued" line of log printout (only done after a
> >   * line that had no enclosing \n). Only to be used by core/arch code
> >   * during early bootup (a continued line is not SMP-safe otherwise).
> > + *
> > + * Please consider pr_line()/vpr_line() functions for SMP-safe continued
> > + * line printing.
> 
> I think the advantage is not limited to SMP-safeness. Reducing the frequency of
> calling printk() will reduce overhead. Also, latency for netconsole will be
> reduced by sending a whole line in one printk().

Hmm. These are very good points, indeed. But do we want to list all
advantages here? I just wanted to mention SMP-unsafe pr_cont/printk(KERN_CONT),
because I also mention pr_line in kern_levels.h.

> > + * Defines a new pr_line varialbe, which would use an implicit
> 
> s/varialbe/variable/ .

Thanks.

> > +#define DEFINE_PR_LINE(lev, name)				\
> > +	char		__line_##name[__PR_LINE_BUF_SZ];	\
> > +	struct pr_line	name = {				\
> > +		.sb	= __SEQ_BUF_INITIALIZER(__line_##name,	\
> > +					__PR_LINE_BUF_SZ),	\
> > +		.level	= lev,					\
> > +	}
> 
> Want a note that
> 
>   static DEFINE_PR_LINE(lev, name);
> 
> won't make "name" variable "static" ?

Interesting point. Any hint what the comment should look like?
Do we want to have static pr_line buffers?

> > +#define DEFINE_PR_LINE_BUF(lev, name, buf, sz)			\
> > +	struct pr_line	name = {				\
> > +		.sb	= __SEQ_BUF_INITIALIZER(buf, (sz)),	\
> > +		.level	= lev,					\
> > +	}
> > +
> 
> I would use this one for the OOM killer. 80 bytes is too short.

80 bytes is quite short for OOM, agreed.

>   static char oom_print_buf[1024];
>   DEFINE_PR_LINE_BUF(level, oom_print_buf);

Do I get it right that you suggest to drop the "size" param?
Do OOM people agree on 1024 bytes stack usage?


> > @@ -131,4 +187,8 @@ extern int
> >  seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
> >  #endif
> >  
> > +extern __printf(2, 0)
> > +int vpr_line(struct pr_line *pl, const char *fmt, va_list args);
> > +extern __printf(2, 3)
> > +int pr_line(struct pr_line *pl, const char *fmt, ...);
> 
> Do we want to mark "asmlinkage" like printk() ?

Dunno, do we? Does code written in assembly call pr_cont that often?
We are not turning pr_line() into syscall anyway.

> > @@ -324,3 +324,60 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
> >  	s->readpos += cnt;
> >  	return cnt;
> >  }
> > +
> > +/**
> > + * vpr_line - Append data to the printk() line buffer
> > + * @pl: the pr_line descriptor
> 
> s/descriptor/structure/ ?

Yeah, I used the term "descriptor", just because it's used in seq_buf.c.
So, it's sort of common in seq_buf.
E.g.
   seq_buf_vprintf(), seq_buf_print_seq(), seq_buf_can_fit() and so on.

> > + * @fmt: printf format string
> > + * @args: va_list of arguments from a printf() type function
> > + *
> > + * Writes a vnprintf() format into the printk() pr_line buffer.
> 
> s/vnprintf/vprintf/ ?

Indeed.
We also need to fix a typo in seq_buf_vprintf() comment then.

	-ss

  reply index

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <201804232233.CIC65675.OJSOMFQOFFHVtL@I-love.SAKURA.ne.jp>
     [not found] ` <CACT4Y+boyw_Qy=y-iTnsKZrtTgF0Hk3nHN_xtqUdX4etgiYDQw@mail.gmail.com>
2018-04-24  1:33   ` printk feature for syzbot? Sergey Senozhatsky
2018-04-24 14:40     ` Steven Rostedt
2018-04-26 10:06     ` Petr Mladek
2018-05-10  4:22       ` Sergey Senozhatsky
2018-05-10 11:30         ` Petr Mladek
2018-05-10 12:11           ` Sergey Senozhatsky
2018-05-10 14:22             ` Steven Rostedt
2018-05-10 14:50         ` Tetsuo Handa
2018-05-11  1:45           ` Sergey Senozhatsky
     [not found]             ` <201805110238.w4B2cIGH079602@www262.sakura.ne.jp>
2018-05-11  6:21               ` Sergey Senozhatsky
2018-05-11  9:17                 ` Dmitry Vyukov
2018-05-11  9:50                   ` Sergey Senozhatsky
2018-05-11 11:58                     ` [PATCH] printk: inject caller information into the body of message Tetsuo Handa
2018-05-17 11:21                       ` Sergey Senozhatsky
2018-05-17 11:52                         ` Sergey Senozhatsky
2018-05-18 12:15                         ` Petr Mladek
2018-05-18 12:25                           ` Dmitry Vyukov
2018-05-18 12:54                             ` Petr Mladek
2018-05-18 13:08                               ` Dmitry Vyukov
2018-05-24  2:21                                 ` Sergey Senozhatsky
2018-05-23 10:19                           ` Tetsuo Handa
2018-05-24  2:14                           ` Sergey Senozhatsky
2018-05-26  6:36                             ` Dmitry Vyukov
2018-06-20  5:44                               ` Dmitry Vyukov
2018-06-20  8:31                                 ` Sergey Senozhatsky
2018-06-20  8:45                                   ` Dmitry Vyukov
2018-06-20  9:06                                     ` Sergey Senozhatsky
2018-06-20  9:18                                       ` Sergey Senozhatsky
2018-06-20  9:31                                         ` Dmitry Vyukov
2018-06-20 11:07                                           ` Sergey Senozhatsky
2018-06-20 11:32                                             ` Dmitry Vyukov
2018-06-20 13:06                                               ` Sergey Senozhatsky
2018-06-22 13:06                                                 ` Tetsuo Handa
2018-06-25  1:41                                                   ` Sergey Senozhatsky
2018-06-25  9:36                                                     ` Dmitry Vyukov
2018-06-27 10:29                                                       ` Tetsuo Handa
2018-09-10 11:20                                                 ` Alexander Potapenko
2018-09-12  6:53                                                   ` Sergey Senozhatsky
2018-09-12 16:05                                                     ` Steven Rostedt
2018-09-13  7:12                                                       ` Sergey Senozhatsky
2018-09-13 12:26                                                         ` Petr Mladek
2018-09-13 14:28                                                           ` Sergey Senozhatsky
2018-09-14  1:22                                                             ` Steven Rostedt
2018-09-14  2:15                                                               ` Sergey Senozhatsky
2018-09-14  6:57                                                             ` Sergey Senozhatsky
2018-09-14 10:37                                                               ` Tetsuo Handa
2018-09-14 11:50                                                                 ` Sergey Senozhatsky [this message]
2018-09-14 12:03                                                                   ` Tetsuo Handa
2018-09-14 12:22                                                                     ` Sergey Senozhatsky
2018-09-19 11:02                                                                       ` Tetsuo Handa
2018-09-24  8:11                                                                         ` Tetsuo Handa
2018-09-27 16:10                                                                           ` Tetsuo Handa
2018-09-28  9:02                                                                             ` Sergey Senozhatsky
2018-09-28  9:09                                                                           ` Sergey Senozhatsky
2018-09-28 11:01                                                                             ` Tetsuo Handa
2018-09-29 10:51                                                                               ` Sergey Senozhatsky
2018-09-29 11:15                                                                                 ` Tetsuo Handa
2018-10-01  2:37                                                                                   ` Sergey Senozhatsky
2018-10-01  2:58                                                                                     ` Sergey Senozhatsky
2018-10-01 11:21                                                                                     ` Tetsuo Handa
2018-10-02  6:38                                                                                       ` Sergey Senozhatsky
2018-10-08 10:31                                                                                         ` Tetsuo Handa
2018-10-08 16:03                                                                                           ` Petr Mladek
2018-10-08 20:48                                                                                             ` Tetsuo Handa
2018-10-09 14:52                                                                                               ` Petr Mladek
2018-10-09 21:19                                                                                                 ` Tetsuo Handa
2018-10-10 10:14                                                                                                   ` Tetsuo Handa
2018-10-11 10:20                                                                                                     ` Tetsuo Handa
2018-10-11 13:47                                                                                                       ` Steven Rostedt
2018-10-08 15:43                                                                                         ` Petr Mladek
2018-09-28  8:56                                                                         ` Sergey Senozhatsky
2018-09-28 11:21                                                                           ` Tetsuo Handa
2018-09-29 11:13                                                                             ` Sergey Senozhatsky
2018-09-29 11:39                                                                               ` Tetsuo Handa
2018-10-01  5:52                                                                               ` Sergey Senozhatsky
2018-10-01  8:37                                                                                 ` Sergey Senozhatsky
2018-10-01 18:06                                                                               ` Steven Rostedt
2018-09-14  1:12                                                         ` Steven Rostedt
2018-09-14  1:55                                                           ` Sergey Senozhatsky
2018-06-21  8:29                                               ` Sergey Senozhatsky
2018-06-20  9:30                                       ` Dmitry Vyukov
2018-06-20 11:19                                         ` Sergey Senozhatsky
2018-06-20 11:25                                           ` Dmitry Vyukov
2018-06-20 11:37                                         ` Fengguang Wu
2018-06-20 12:31                                           ` Dmitry Vyukov
2018-06-20 12:41                                             ` Fengguang Wu
2018-06-20 12:45                                               ` Dmitry Vyukov
2018-06-20 12:48                                                 ` Fengguang Wu
2018-05-11 13:37                     ` printk feature for syzbot? Steven Rostedt
2018-05-15  5:20                       ` Sergey Senozhatsky
2018-05-15 14:39                         ` Steven Rostedt
2018-05-11 11:02                 ` [PATCH] printk: fix possible reuse of va_list variable Tetsuo Handa
2018-05-11 11:27                   ` Sergey Senozhatsky
2018-05-17 11:57                   ` Petr Mladek

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