All of lore.kernel.org
 help / color / mirror / Atom feed
From: Richard Weinberger <richard@nod.at>
To: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>, tglx <tglx@linutronix.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Thomas Meyer <thomas@m3y3r.de>
Subject: Re: [PATCH printk-rework 09/12] um: synchronize kmsg_dumper
Date: Mon, 1 Feb 2021 21:40:04 +0100 (CET)	[thread overview]
Message-ID: <790609565.351317.1612212004428.JavaMail.zimbra@nod.at> (raw)
In-Reply-To: <87v9bbzga2.fsf@jogness.linutronix.de>

John,

----- Ursprüngliche Mail -----
>>> The line was previously synchronized for the kmsg_dump_get_line()
>>> call. But yes, it was not synchronized after the call, which is a bug if
>>> the dump is triggered on multiple CPUs simultaneously. The commit
>>> message should also mention that it is handling that bug.
>>> 
>>>> IMHO, this patch is not needed.
>>> 
>>> I am not familiar enough with ARCH=um to know if dumps can be triggered
>>> on multiple CPUs simultaneously. Perhaps ThomasM or Richard can chime in
>>> here.
>>
>> Well, uml has no SMP support, so no parallel dumps. :-)
> 
> When I grep through arch/um, I see many uses of spinlocks. This would
> imply that uml at least has some sort of preemption model where they are
> needed. Dumps can trigger from any context and from multiple paths.
> 
> If you are sure that this is no concern, then I will drop this patch
> from my series.

Currently uml selects ARCH_NO_PREEMPT, so no preemtion too.
We have spinlocks at obvious places in arch/um/ just to be ready if uml supports
SMP at some point.
Does your patch have drawbacks right now for uml? If not, I'd suggest to keep it.

Thanks,
//richard


  reply	other threads:[~2021-02-01 20:41 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 21:15 [PATCH printk-rework 00/12] printk: remove logbuf_lock John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 01/12] printk: kmsg_dump: remove unused fields John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 02/12] printk: refactor kmsg_dump_get_buffer() John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 03/12] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code John Ogness
     [not found]   ` <YBQgTQYTA5p6Wgj6@alley>
2021-02-01  9:49     ` John Ogness
2021-02-02 12:31       ` Petr Mladek
2021-01-26 21:15 ` [PATCH printk-rework 04/12] printk: define CONSOLE_LOG_MAX in printk.h John Ogness
     [not found]   ` <YBQtbKrdwUAZQB9v@alley>
2021-02-01  8:24     ` LINE_MAX: was: " John Ogness
2021-02-02 11:22       ` Petr Mladek
2021-01-26 21:15 ` [PATCH printk-rework 05/12] printk: use seqcount_latch for clear_seq John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 06/12] printk: use atomic64_t for devkmsg_user.seq John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 07/12] printk: add syslog_lock John Ogness
2021-02-01 12:26   ` Petr Mladek
2021-02-01 13:11     ` John Ogness
2021-02-02 12:50       ` Petr Mladek
2021-01-26 21:15 ` [PATCH printk-rework 08/12] printk: introduce a kmsg_dump iterator John Ogness
2021-02-01 13:17   ` Petr Mladek
2021-02-01 13:32     ` John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 09/12] um: synchronize kmsg_dumper John Ogness
2021-02-01 10:26   ` Petr Mladek
2021-02-01 14:15   ` Petr Mladek
2021-02-01 16:51     ` John Ogness
2021-02-01 16:54       ` Richard Weinberger
2021-02-01 20:25         ` John Ogness
2021-02-01 20:40           ` Richard Weinberger [this message]
2021-02-02 13:26       ` Petr Mladek
2021-01-26 21:15 ` [PATCH printk-rework 10/12] hv: " John Ogness
2021-01-27 21:32   ` Michael Kelley
2021-02-01 10:56     ` John Ogness
2021-01-26 21:15 ` [PATCH printk-rework 11/12] printk: remove logbuf_lock John Ogness
2021-02-02  9:15   ` Petr Mladek
2021-02-02 11:41     ` John Ogness
2021-02-02 16:11       ` Petr Mladek
2021-01-26 21:15 ` [PATCH printk-rework 12/12] printk: kmsg_dump: remove _nolock() variants John Ogness
2021-02-02  9:45   ` 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=790609565.351317.1612212004428.JavaMail.zimbra@nod.at \
    --to=richard@nod.at \
    --cc=john.ogness@linutronix.de \
    --cc=linux-kernel@vger.kernel.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=thomas@m3y3r.de \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.