linux-kernel - Re: 3.8-rc regression with pps-ldisc due to 70ece7a731

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Date:	6 Feb 2013 14:45:14 -0500
From:	"George Spelvin" <linux@...izon.com>
To:	linux@...izon.com, peter@...leysoftware.com
Cc:	jslaby@...e.cz, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: 3.8-rc regression with pps-ldisc due to 70ece7a731

> Tight coupling is what caused this to break in the first place -- I
> don't think tighter coupling is the right answer.

Agreed.  But given that n_tty already knows there are wrappers, it would
have been possible to find a cleaner way to access an "aux pointer" in
the tty structure, if that's what was desired.

> You are not supposed to receive ldisc->dcd_change() calls outside
> the open()/close() pair.

Yes, I figured that out.  I was wondering because I couldn't see any
way that the serial interrupt hander was blocked or masked, but
then I figured out that it's not, but instead the TTY_LDISC flag
is used.

At the time the open() method is called, the flag is cleared, which makes
tty_ldisc_ref() return NULL, which prevents calling the ldisc methods.

> In the patch series I sent, I changed the BUG_ON() to WARN_ON_ONCE().
> Please reply to that patch with the snipped kernel log output if it
> warns in your testing and we'll go from there.

I really doubt it will.  The entire code change and comment was
just caution on my part.

>> (Have I mentioned how ANNOYING it is when the kernel dumps more than
>> 50 lines of crash message to the console screen and then locks
>> the keyboard so I can't scroll back?)

> netconsole on 2nd machine (see Documentation/networking/netconsole.txt)

Oh, that survives interrupt crashes?  Thank you!
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