From: John Ogness <john.ogness@linutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
kexec@lists.infradead.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 0/4] printk: reimplement LOG_CONT handling
Date: Sat, 18 Jul 2020 16:48:55 +0206 [thread overview]
Message-ID: <87blkcanps.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <CAHk-=wivdy6-i=iqJ1ZG9YrRzaS0_LHHEPwb9KJg-S8i-Wm30w@mail.gmail.com>
On 2020-07-17, Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Make sure you test the case of "fast concurrent readers". The last
> time we did things like this, it was a disaster, because a concurrent
> reader would see and return the _incomplete_ line, and the next entry
> was still being generated on another CPU.
>
> The reader would then decide to return that incomplete line, because
> it had something.
>
> And while in theory this could then be handled properly in user space,
> in practice it wasn't. So you'd see a lot of logging tools that would
> then report all those continuations as separate log events.
>
> Which is the whole point of LOG_CONT - for that *not* to happen.
I expect this is handled correctly since the reader is not given any
parts until a full line is ready, but I will put more focus on testing
this to make sure. Thanks for the regression and testing tips.
> So this is just a heads-up that I will not pull something that breaks
> LOG_CONT because it thinks "user space can handle it". No. User space
> does not handle it, and we need to handle it for the user.
Understood. Petr and Sergey are also strict about this. We are making a
serious effort to avoid breaking things for userspace.
John Ogness
_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
next prev parent reply other threads:[~2020-07-18 14:43 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 23:48 [PATCH 0/4] printk: reimplement LOG_CONT handling John Ogness
2020-07-17 23:48 ` [PATCH 1/4] printk: ringbuffer: support dataless records John Ogness
2020-07-20 14:49 ` John Ogness
2020-07-17 23:48 ` [PATCH 2/4] printk: store instead of processing cont parts John Ogness
2020-07-19 14:35 ` Sergey Senozhatsky
2020-07-19 18:27 ` Linus Torvalds
2020-07-20 1:50 ` Sergey Senozhatsky
2020-07-20 18:30 ` Linus Torvalds
2020-07-21 3:53 ` Joe Perches
2020-07-21 14:42 ` Sergey Senozhatsky
2020-07-21 14:57 ` John Ogness
2020-07-29 2:03 ` Sergey Senozhatsky
2020-07-21 15:40 ` Linus Torvalds
2020-07-28 2:22 ` Sergey Senozhatsky
2020-07-17 23:48 ` [PATCH 3/4] printk: process cont records during reading John Ogness
2020-07-17 23:48 ` [PATCH 4/4] ipconfig: cleanup printk usage John Ogness
2020-07-18 0:00 ` [PATCH 0/4] printk: reimplement LOG_CONT handling Linus Torvalds
2020-07-18 14:42 ` John Ogness [this message]
2020-07-18 17:42 ` Linus Torvalds
2020-08-11 16:05 ` Petr Mladek
2020-08-12 16:39 ` POC: Alternative solution: " Petr Mladek
2020-08-13 0:24 ` John Ogness
2020-08-13 5:18 ` Sergey Senozhatsky
2020-08-13 7:44 ` John Ogness
2020-08-13 8:41 ` Petr Mladek
2020-08-13 10:29 ` John Ogness
2020-08-13 11:30 ` Petr Mladek
2020-08-14 3:34 ` Sergey Senozhatsky
2020-08-14 8:16 ` John Ogness
2020-08-14 9:12 ` Petr Mladek
2020-08-13 11:54 ` Sergey Senozhatsky
2020-08-14 9:04 ` Petr Mladek
2020-08-14 22:46 ` Linus Torvalds
2020-08-14 23:52 ` Joe Perches
2020-08-15 2:33 ` Linus Torvalds
2020-08-15 3:08 ` Joe Perches
2020-08-15 9:25 ` David Laight
2020-08-15 5:41 ` Sergey Senozhatsky
2020-08-13 7:51 ` Petr Mladek
2020-08-13 7:31 ` Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87blkcanps.fsf@jogness.linutronix.de \
--to=john.ogness@linutronix.de \
--cc=gregkh@linuxfoundation.org \
--cc=kexec@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=rostedt@goodmis.org \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sergey.senozhatsky@gmail.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox