From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH next v2 1/3] printk: inline log_output(),log_store() in vprintk_store()
Date: Fri, 4 Dec 2020 09:26:26 +0100 [thread overview]
Message-ID: <X8nysl/ne1f0nlKe@alley> (raw)
In-Reply-To: <87v9diyhza.fsf@jogness.linutronix.de>
On Thu 2020-12-03 17:31:29, John Ogness wrote:
> On 2020-12-03, Petr Mladek <pmladek@suse.com> wrote:
> >> + if (lflags & LOG_CONT) {
> >> + prb_rec_init_wr(&r, text_len);
> >> + if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
> >> + memcpy(&r.text_buf[r.info->text_len], text, text_len);
> >> + r.info->text_len += text_len;
> >> +
> >> + if (lflags & LOG_NEWLINE) {
> >> + r.info->flags |= LOG_NEWLINE;
> >> + prb_final_commit(&e);
> >> + } else {
> >> + prb_commit(&e);
> >> + }
> >> +
> >> + return text_len;
> >> + }
> >> + }
> >> +
> >> + prb_rec_init_wr(&r, text_len);
> >
> > This is called in both branches. I would do it just once at the
> > beginning.
>
> Actually that leads to a crash when prb_reserve_in_last() fails and the
> fallback code uses a record that prb_reserve_in_last() has already
> touched. The implementation of prb_reserve_in_last() would have to be
> changed so that failure guarantees that @r has not been
> modified. Currently prb_reserve_in_last() can fail after modifying @r.
I see. It would deserve a comment so that nobody repeats my mistake
again. I am sure that I would be able to do it once again few
months from now ;-)
> >> + if (!prb_reserve(&e, prb, &r)) {
> >> + /* truncate the message if it is too long for empty buffer */
> >> + truncate_msg(&text_len, &trunc_msg_len);
> >> +
> >> + prb_rec_init_wr(&r, text_len + trunc_msg_len);
> >> + if (!prb_reserve(&e, prb, &r))
> >> + return 0;
> >> + }
> >> +
> >> + /* fill message */
> >> + memcpy(&r.text_buf[0], text, text_len);
> >> + if (trunc_msg_len)
> >> + memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
> >> + r.info->text_len = text_len + trunc_msg_len;
> >> + r.info->facility = facility;
> >> + r.info->level = level & 7;
> >> + r.info->flags = lflags & 0x1f;
> >> + r.info->ts_nsec = ts_nsec;
> >
> > This is the only location where ts_nsec is used. I would remove the
> > variable and call:
> >
> > r.info->ts_nsec = local_clock();
>
> My reason for grabbing the clock at the beginning is so that the
> timestamp is as close to the printk() call as possible. IMHO it is a
> more deterministic timestamp than if it is taken after reservation(s)
> and sprint'ing. I prefer to keep it as it is, but will not object if
> such a change is necessary for mailine acceptance.
Fair enough. It would deserve a comment as well.
Best Regards,
Petr
next prev parent reply other threads:[~2020-12-04 8:27 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 20:53 [PATCH next v2 0/3] printk: remove logbuf_lock John Ogness
2020-12-01 20:53 ` [PATCH next v2 1/3] printk: inline log_output(),log_store() in vprintk_store() John Ogness
2020-12-03 15:57 ` Petr Mladek
2020-12-03 16:25 ` John Ogness
2020-12-04 6:13 ` Sergey Senozhatsky
2020-12-04 8:26 ` Petr Mladek [this message]
2020-12-01 20:53 ` [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t John Ogness
2020-12-04 9:12 ` Petr Mladek
2020-12-06 20:23 ` John Ogness
2020-12-07 9:34 ` Peter Zijlstra
2020-12-07 10:03 ` John Ogness
2020-12-07 12:56 ` Peter Zijlstra
2020-12-07 12:56 ` Petr Mladek
2020-12-07 16:46 ` David Laight
2020-12-08 20:34 ` Sergey Senozhatsky
2020-12-08 22:30 ` John Ogness
2020-12-09 1:04 ` Sergey Senozhatsky
2020-12-09 8:16 ` Peter Zijlstra
2020-12-09 9:22 ` Sergey Senozhatsky
2020-12-09 10:46 ` Sergey Senozhatsky
2020-12-09 11:00 ` Peter Zijlstra
2020-12-09 11:28 ` Sergey Senozhatsky
2020-12-09 12:29 ` Peter Zijlstra
2020-12-09 8:07 ` Peter Zijlstra
2020-12-01 20:53 ` [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock John Ogness
2020-12-04 6:41 ` Sergey Senozhatsky
2020-12-06 20:44 ` John Ogness
2020-12-04 15:52 ` devkmsg: was " Petr Mladek
2020-12-06 20:51 ` John Ogness
2020-12-07 9:56 ` Petr Mladek
2020-12-04 15:57 ` syslog: was: " Petr Mladek
2020-12-06 21:06 ` John Ogness
2020-12-07 10:01 ` Petr Mladek
2020-12-04 16:10 ` recursion handling: " Petr Mladek
2020-12-05 4:25 ` Sergey Senozhatsky
2020-12-06 22:08 ` John Ogness
2020-12-05 9:41 ` Sergey Senozhatsky
2020-12-06 22:17 ` John Ogness
2020-12-06 21:44 ` John Ogness
2020-12-07 11:17 ` Petr Mladek
2020-12-04 16:15 ` vprintk_store: was: " Petr Mladek
2020-12-06 22:30 ` John Ogness
2020-12-07 12:46 ` Petr Mladek
2020-12-04 16:19 ` consoles: " Petr Mladek
2020-12-05 4:39 ` Sergey Senozhatsky
2020-12-07 9:50 ` Petr Mladek
2020-12-08 20:51 ` Sergey Senozhatsky
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