Re: manipulating sigmask from filesystems and drivers

[Linus Torvalds]

On Thu, 1 Aug 2002, David Woodhouse wrote:
> 
> [e-mail] said:
> >  They should be waiting in TASK_UNINTERRUPTIBLE, and we should add a
> > flag  to distinguish between "increases load average" and "doesn't".
> 
> The disadvantage of this approach is that it encourages people to be lazy
> and sleep with signals disabled, instead of implementing proper cleanup
> code. 
> 
> I'm more in favour of removing TASK_UNINTERRUPTIBLE entirely, or at least 
> making people apply for a special licence to be permitted to use it :)

Can't do that.

Easy reason: there are tons of code sequences that _cannot_ take signals.  
The only way to make a signal go away is to actually deliver it, and there
are documented interfaces that are guaranteed to complete without
delivering a signal. The trivial case is a disk read: real applications
break if you return partial results in order to handle signals in the
middle.

In short, this is not something that can be discussed. It's a cold fact, a
law of UNIX if you will.

There are enough reasons to discourage people from using uninterruptible 
sleep ("this f*cking application won't die when the network goes down") 
that I don't think this is an issue. We need to handle both cases, and 
while we can expand on the two cases we have now, we can't remove them.

		Linus