From: Petr Mladek <pmladek@suse.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush()
Date: Thu, 1 Sep 2016 10:17:33 +0200 [thread overview]
Message-ID: <20160901081732.GV4866@pathway.suse.cz> (raw)
In-Reply-To: <20160901075507.GA504@swordfish>
On Thu 2016-09-01 16:55:07, Sergey Senozhatsky wrote:
> On (08/30/16 13:19), Petr Mladek wrote:
> >
> > I see. But then we will need to be more careful because printk_func
> > and printk_func_saved will be manipulated in different contexts:
> > normal, irq, nmi. A solution might be using an atomic counter
> > and selecting the right vprintk_func according to the value.
>
> alt_printk_enter() must be done with local IRQs disabled. so IRQ cannot
> race with `normal' alt_printk. other IRQs cannot race with the current IRQ,
> because we have local IRQs disabled. the only thing that can race here is - NMI.
> both `normal' and IRQ alt_printk can use the same per-CPU buffer, they never
> race. NMI needs to have its own.
Yes. Well, my concern was how to atomically change the printk_func
pointer and save the previous value at the same time. You could not
use locks because NMIs are involved.
Best Regards,
Petr
prev parent reply other threads:[~2016-09-01 8:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-29 12:32 [PATCH] printk/nmi: avoid direct printk()-s from __printk_nmi_flush() Sergey Senozhatsky
2016-08-29 15:16 ` Petr Mladek
2016-08-30 1:07 ` Sergey Senozhatsky
2016-08-30 7:58 ` Sergey Senozhatsky
2016-08-30 9:04 ` Petr Mladek
2016-08-30 9:39 ` Sergey Senozhatsky
2016-08-30 11:19 ` Petr Mladek
2016-08-31 4:00 ` Sergey Senozhatsky
2016-09-01 7:55 ` Sergey Senozhatsky
2016-09-01 8:17 ` Petr Mladek [this message]
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