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
next prev parent 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
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