From: Petr Mladek <pmladek@suse.com>
To: Michal Hocko <mhocko@suse.com>
Cc: John Ogness <john.ogness@linutronix.de>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] printk: Enough to disable preemption in printk deferred context
Date: Wed, 19 Apr 2023 12:31:44 +0200 [thread overview]
Message-ID: <ZD_DED6ttnLvUJsI@alley> (raw)
In-Reply-To: <ZD+lBU1PGkLadDMT@dhcp22.suse.cz>
On Wed 2023-04-19 10:23:33, Michal Hocko wrote:
> On Wed 19-04-23 09:42:10, Petr Mladek wrote:
> > The comment above printk_deferred_enter()/exit() definition claims
> > that it can be used only when interrupts are disabled.
> >
> > It was required by the original printk_safe_log_store() implementation.
> > The code provided lockless synchronization between a single writer and
> > a single reader. The interrupt and the normal context shared the same
> > buffer.
> >
> > The commit 93d102f094be ("printk: remove safe buffers") removed
> > these temporary buffers. Instead, the messages are stored directly into
> > the new global lockless buffer which supports multiple parallel writers.
> >
> > As a result, it is safe to interrupt one writer now. The preemption still
> > has to be disabled because the deferred context is CPU specific.
>
> Thanks for the clarification and explanation.
>
> > Fixes: 93d102f094be ("printk: remove safe buffers")
>
> Is this a fix though? I would expect some users to be changed from irq
> to preempt to disabling to be considered a fix.
Yeah, I am not sure about the Fixes tag either. I wanted to cross-link
the two commits. But it is probably enough to mention it in the commit
message.
Best Regards,
Petr
next prev parent reply other threads:[~2023-04-19 10:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-19 7:42 [PATCH] printk: Enough to disable preemption in printk deferred context Petr Mladek
2023-04-19 8:23 ` Sergey Senozhatsky
2023-04-19 8:23 ` Michal Hocko
2023-04-19 10:31 ` Petr Mladek [this message]
2023-04-19 9:05 ` John Ogness
2023-04-19 12:03 ` Petr Mladek
2023-04-19 12:14 ` Michal Hocko
2023-04-19 13:45 ` John Ogness
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