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Date: Thu, 1 Aug 2002 12:09:04 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: David Howells <dhowells@redhat.com>
cc: <alan@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: manipulating sigmask from filesystems and drivers
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On Wed, 31 Jul 2002, David Howells wrote:
> 
> Can you comment on whether a driver is allowed to block signals like this, and
> whether they should be waiting in TASK_UNINTERRUPTIBLE?

They should be waiting in TASK_UNINTERRUPTIBLE, and we should add a flag 
to distinguish between "increases load average" and "doesn't". So you 
could have

	TASK_WAKESIGNAL - wake on all signals
	TASK_WAKEKILL	- wake on signals that are deadly
	TASK_NOSIGNAL	- don't wake on signals
	TASK_LOADAVG	- counts toward loadaverage

	#define TASK_UNINTERRUPTIBLE	(TASK_NOSIGNAL | TASK_LOADAVG)
	#define TASK_INTERRUPTIBLE	TASK_WAKESIGNAL

and then people who wanted to could use other combinations. The
TASK_WAKEKILL thing is useful - there are many loops that cannot exit
until they have a result, simply because the calling conventions require 
that. Th emost common example is disk wait.

HOWEVER, if they are killed by a signal, the calling convention doesn't
matter, and the read() or whatever could just return 0 (knowing that the
process will never see it), and leave a locked page locked. Things like 
generic_file_read() could easily use this, and make processes killable 
even when they are waiting for a hung NFS mount - regardless of any soft 
mount issues, and without NFS having to have special code.

In the end, I'm too lazy, and I don't care. So I can only tell you how it 
_should_ be done, and maybe you can tell somebody else until the sucker to 
actually do it is found.

		Linus

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