From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Jan Kara <jack@suse.cz>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.com>, Tejun Heo <tj@kernel.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Byungchul Park <byungchul.park@lge.com>,
vlevenetz@mm-sol.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v10 1/2] printk: Make printk() completely async
Date: Wed, 24 Aug 2016 10:33:14 +0900 [thread overview]
Message-ID: <20160824013314.GB452@swordfish> (raw)
In-Reply-To: <20160823121903.GD4866@pathway.suse.cz>
On (08/23/16 14:19), Petr Mladek wrote:
> > the other thing I just thought of is doing something as follows
> > !!!not tested, will not compile, just an idea!!!
> >
> > ---
> >
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 6e260a0..bb8d719 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -1789,6 +1789,7 @@ asmlinkage int vprintk_emit(int facility, int level,
> > printk_delay();
> >
> > local_irq_save(flags);
> > + printk_nmi_enter();
> > this_cpu = smp_processor_id();
>
> Huh, this looks very interesting but I am afraid that it will not fly.
> The problem is that vprintk_nmi() is safe only when it is used
> exclusively in NMI.
>
> The following could happen with your code:
sure. I took NMI as a quick and easy example that did not require a lot
of words to explain because you guys are familiar with NMI printing.
the thing is - we don't have to share the same buffer with the actual NMI,
but instead have our own small 'alternative-printk' per-cpu buffers (a page
or two, perhaps). it's up to `printk_func' that we set up at the entry point
and flush function that we execute later. vprintk_nmi() writes to
this_cpu_ptr(&nmi_print_seq), vprintk_alter() will write to
this_cpu_ptr(&alt_print_seq), for example. the same with flushing:
printk_nmi_flush reads in from per_cpu(nmi_print_seq); alter-printk flush
can read from per_cpu(alt_print_seq).
[..]
> The lockless handling of the NMI per-CPU buffer already is not
> trivial. I would be afraid to add more hacks to make
> it writable in all contexts.
yes. we can reuse the idea of NMI printk and most of the code. the thing
we really care is `struct nmi_seq_buf' assigned to this particular CPU,
and there can be several seq_buffer-s.
> I am sorry about the bad news. This was so promising on the first
> look.
it's not dead yet ;)
-ss
next prev parent reply other threads:[~2016-08-24 1:34 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-04 16:57 [PATCH v10 0/2] printk: Make printk() completely async Sergey Senozhatsky
2016-04-04 16:57 ` [PATCH v10 1/2] " Sergey Senozhatsky
2016-04-04 22:51 ` Andrew Morton
2016-04-05 5:17 ` Sergey Senozhatsky
2016-04-05 7:39 ` Sergey Senozhatsky
2016-04-06 0:19 ` Sergey Senozhatsky
2016-04-06 8:27 ` Jan Kara
2016-04-07 9:48 ` Sergey Senozhatsky
2016-04-07 12:08 ` Sergey Senozhatsky
2016-04-07 13:15 ` Jan Kara
2016-08-10 21:17 ` Viresh Kumar
2016-08-12 9:44 ` Petr Mladek
2016-08-15 14:26 ` Vladislav Levenetz
2016-08-16 9:04 ` Petr Mladek
2016-08-18 2:27 ` Sergey Senozhatsky
2016-08-18 9:33 ` Petr Mladek
2016-08-18 9:51 ` Sergey Senozhatsky
2016-08-18 10:56 ` Petr Mladek
2016-08-19 6:32 ` Sergey Senozhatsky
2016-08-19 9:54 ` Petr Mladek
2016-08-19 19:00 ` Jan Kara
2016-08-20 5:24 ` Sergey Senozhatsky
2016-08-22 4:15 ` Sergey Senozhatsky
2016-08-23 12:19 ` Petr Mladek
2016-08-24 1:33 ` Sergey Senozhatsky [this message]
2016-08-25 21:10 ` Petr Mladek
2016-08-26 1:56 ` Sergey Senozhatsky
2016-08-26 8:20 ` Sergey Senozhatsky
2016-08-30 9:29 ` Petr Mladek
2016-08-31 2:31 ` Sergey Senozhatsky
2016-08-31 9:38 ` Petr Mladek
2016-08-31 12:52 ` Sergey Senozhatsky
2016-09-01 8:58 ` Petr Mladek
2016-09-02 7:58 ` Sergey Senozhatsky
2016-09-02 15:15 ` Petr Mladek
2016-09-06 7:16 ` Sergey Senozhatsky
2016-08-23 13:03 ` Petr Mladek
2016-08-23 13:48 ` Petr Mladek
2016-04-04 16:57 ` [PATCH v10 2/2] printk: Make wake_up_klogd_work_func() async Sergey Senozhatsky
2016-08-23 3:32 [PATCH v10 1/2] printk: Make printk() completely async Andreas Mohr
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