Re: [PATCH] might_sleep() improvements

[Nick Piggin]

Mitchell Blank Jr wrote:

> Nick Piggin wrote:
>
> > > Andrew - I thought this might be appropriate for -mm kernels.
> > >
> > > This patch makes the following improvements to might_sleep():
> > >
> > > o Add a "might_sleep_if()" macro for when we might sleep only if some
> > > condition is met.  I think this is a bit better than the currently used
> > > "if (cond) might_sleep();" since it's clearer that the test won't be
> > > compiled in if spinlock sleep debugging is turned off.  (Obviously
> > > gcc is smart enough to omit simple conditions in that case)  It also
> > > looks cleaner, IMO.  Think of it as analogous to BUG()/BUG_ON().
> > I think these should be pushed down to where the sleeping
> > actually happens if possible.
>
> No, you want to generate the warning as early as possible in case the
> sleeping case happens very infrequently.  For instance:
>
> 	newskb = skb_unshare(skb, GFP_KERNEL);
>
> might not even need to do any allocation (much less a sleep) in 99.9% of
> cases, but it's still a bug if it's called in atomic context and we want
> spinlock sleep debugging to catch that for us.

Yeah well in this case I guess skb_unshare is as low as might_sleep
can be pushed. I guess I don't have a problem with might_sleep_if as
long as its used nicely.


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