linux-kernel - Re: Nonterministic hang during bootconsole/console handover on ath79

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Message-Id: <20160322084046.7196890a7c157503cd0ea0d5@gmail.com>
Date:	Tue, 22 Mar 2016 08:40:46 +0300
From:	Antony Pavlov <antonynpavlov@...il.com>
To:	Matthias Schiffer <mschiffer@...verse-factory.net>
Cc:	Ralf Baechle <ralf@...ux-mips.org>, gregkh@...uxfoundation.org,
	jslaby@...e.com, linux-mips@...ux-mips.org,
	linux-serial@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Mamonov <pmamonov@...il.com>
Subject: Re: Nonterministic hang during bootconsole/console handover on
 ath79

On Tue, 22 Mar 2016 00:02:57 +0100
Matthias Schiffer <mschiffer@...verse-factory.net> wrote:

> Hi,
> we're experiencing weird nondeterministic hangs during bootconsole/console
> handover on some ath79 systems on OpenWrt. I've seen this issue myself on
> kernel 3.18.23~3.18.27 on a AR7241-based system, but according to other
> reports ([1], [2]) kernel 4.1.x is affected as well, and other SoCs like
> QCA953x likewise.
> 
> See the log below for the exact place it hangs; the log was taken in during
> a good boot; a bad boot will just hang forever at the marked location. The
> issue is extremely hard to debug, as changing the timing in any way (like
> adding additional printk) will usually make it work without problems. (Even
> recompiling the kernel with the same config, but different uname timestamp
> will make the occurence more or less likely)
> 
> My theory is the following:
> 
> As soon as ttyS0 is detected and installed as the console, there are two
> console drivers active on the serial port at the same time: early0 and
> ttyS0. I suspect that the hang occurs when the primitive early0
> implementation prom_putchar_ar71xx waits indefinitely on THRE,

Can you use EJTAG to prove your theory?

-- 
Best regards,
  Antony Pavlov