From: Steven Rostedt <rostedt@goodmis.org>
To: Jan Kara <jack@suse.cz>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Cong Wang <xiyou.wangcong@gmail.com>,
Dave Hansen <dave.hansen@intel.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
"yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH v2] printk: Add console owner and waiter logic to load balance console writes
Date: Fri, 3 Nov 2017 07:18:24 -0400 [thread overview]
Message-ID: <20171103071824.1cf629ee@vmware.local.home> (raw)
In-Reply-To: <20171103101953.GA5280@quack2.suse.cz>
On Fri, 3 Nov 2017 11:19:53 +0100
Jan Kara <jack@suse.cz> wrote:
> Hi,
>
> On Thu 02-11-17 13:06:05, Steven Rostedt wrote:
> > + if (spin) {
> > + /* We spin waiting for the owner to release us */
> > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
> > + /* Owner will clear console_waiter on hand off */
> > + while (!READ_ONCE(console_waiter))
> > + cpu_relax();
>
> Hum, what prevents us from rescheduling here? And what if the process
> stored in console_owner is scheduled out? Both seem to be possible with
> CONFIG_PREEMPT kernel? Unless I'm missing something you will need to
> disable preemption in some places...
Yes you are missing something ;-)
>
> Other than that I like the simplicity of your approach.
>
> Honza
>
> > +
> > + spin_release(&console_owner_dep_map, 1, _THIS_IP_);
> > + printk_safe_exit_irqrestore(flags);
The above line re-enables interrupts. And is done for both the
console_owner and the console_waiter. These are only held with
interrupts disabled. Nothing will preempt it. In fact, if it could,
lockdep would complain (it did in when I screwed it up at first ;-)
-- Steve
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prev parent reply other threads:[~2017-11-03 11:18 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 11:28 [PATCH] mm: don't warn about allocations which stall for too long Tetsuo Handa
2017-10-26 11:41 ` Michal Hocko
2017-11-08 10:30 ` peter enderborg
2017-11-09 8:52 ` Michal Hocko
2017-11-09 9:34 ` peter enderborg
2017-11-09 10:09 ` Michal Hocko
2017-11-09 10:19 ` Tetsuo Handa
2017-10-26 14:37 ` Johannes Weiner
2017-10-31 19:32 ` Steven Rostedt
2017-11-01 8:30 ` Vlastimil Babka
2017-11-01 13:38 ` Petr Mladek
2017-11-01 15:36 ` Steven Rostedt
2017-11-02 11:46 ` Petr Mladek
2017-11-02 14:49 ` Steven Rostedt
2017-11-01 15:33 ` Steven Rostedt
2017-11-01 17:42 ` Vlastimil Babka
2017-11-01 17:54 ` Steven Rostedt
2017-11-02 8:53 ` Sergey Senozhatsky
2017-11-02 9:14 ` Sergey Senozhatsky
2017-11-02 14:55 ` Steven Rostedt
2017-11-02 12:55 ` Michal Hocko
2017-11-02 15:56 ` Steven Rostedt
2017-11-02 17:06 ` [PATCH v2] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt
2017-11-02 17:10 ` Steven Rostedt
2017-11-02 17:38 ` Steven Rostedt
2017-11-03 10:19 ` Jan Kara
2017-11-03 11:18 ` Steven Rostedt [this message]
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