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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Maninder Singh <maninder1.s@samsung.com>,
	sergey.senozhatsky@gmail.com, rostedt@goodmis.org,
	linux-kernel@vger.kernel.org, a.sahrawat@samsung.com,
	pankaj.m@samsung.com, v.narang@samsung.com
Subject: Re: [PATCH 2/2] printk: make sure to print log on console.
Date: Fri, 1 Jun 2018 18:18:23 +0900	[thread overview]
Message-ID: <20180601091823.GA1841@jagdpanzerIV> (raw)
In-Reply-To: <20180601085356.kncuat7epkbtythv@pathway.suse.cz>

On (06/01/18 10:53), Petr Mladek wrote:
> [...]
> 
> > So I'd say that most likely the following scenarios can suffer:
> > 
> > - NMI comes in, sets loglevel to X, printk-s some data, restores the
> >   loglevel back to Y
> > - IRQ comes in [like sysrq, etc] comes in and does the same thing
> > - software exception comes in and does the same thing [e.g. bust_spinlocks()
> >   at arch/s390/mm/fault.c]
> 
> 
> My view is:
> 
> The race with another printk() (console_lock owner) is much more
> likely than a race between two CPUs manipulating console_loglevel.

The race with console_loglevel manipulation from another CPU was not
the main point [it is unlikely, like I said in my "nitpick"].
The point was

	NMI / printk_safe section

	saved_console_loglevel = console_loglevel
	console_loglevel = A

	printk
	printk
	printk

	console_loglevel = saved_console_loglevel
	iret

Is not handled.

> The proposed patch seems to be in the right direction. It is supposed
> to fix the most likely scenario.

Could be.

> I am personally fine with this partial solution for now. We could
> always make it better if people meet the other scenarios.

I don't have objections. But I'd prefer to see real uses cases and
to know why partial solution is good enough in this case, even though
we know that NMI / printk_safe() messages may be lost due to very same
problem.

	-ss

  parent reply	other threads:[~2018-06-01  9:18 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20180531102246epcas5p2f1cbc6ff217172e12e2f78bb88eb4a7e@epcas5p2.samsung.com>
2018-05-31 10:19 ` Maninder Singh
2018-05-31 10:52   ` Sergey Senozhatsky
2018-05-31 12:21     ` Petr Mladek
2018-06-01  4:40       ` Sergey Senozhatsky
2018-06-01  8:53         ` Petr Mladek
2018-06-01  9:09           ` Petr Mladek
2018-06-01  9:37             ` Sergey Senozhatsky
2018-06-01  9:18           ` Sergey Senozhatsky [this message]
     [not found]       ` <CGME20180531102246epcas5p2f1cbc6ff217172e12e2f78bb88eb4a7e@epcms5p5>
2018-06-01  8:42         ` Vaneet Narang
2018-06-01  9:34           ` Sergey Senozhatsky
2018-05-31 13:27   ` Petr Mladek

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