Re: illegal instructions / irqs disabled warning

["Johannes Berg" <johannes@sipsolutions.net>]

Paul Mackerras wrote:
>> So I run across this warning:
>> [ 2724.595549] Debug: sleeping function called from invalid context at
>> arch/ppc/kernel/traps.c:528
>> [ 2724.595563] in_atomic():0, irqs_disabled():1
>
> Hmmm.  What kernel version is this?  I assume you are using ARCH=ppc,
> is that right?

2.6.15-rc5, IIRC (might have been rc1, I currently need to use both
kernels depending on what I want to do), and yes, ARCH=ppc.

> No, it doesn't mean that.  However, if the page isn't in memory,
> __copy_from_user_inatomic won't try to bring it in if it has been
> called from an atomic context (i.e. preempt or interrupts disabled).

Good, thanks. So essentially __copy_from_user has the same logic (since it
just calls __copy_from_user_inatomic) but calls might_sleep() to show the
developer what he's doing wrong although it won't actually hurt. Right?

> The real question is why we have interrupts disabled in the illegal
> instruction handler.  There was a reason why I wanted interrupts
> disabled on entry to program_check_exception which I don't recall
> clearly at the moment, but I think program_check_exception should be
> doing a local_irq_enable() at some point (and it also shouldn't be
> trying to emulate instructions for the kernel).

I don't have the code here right now but I did have a userspace program
that it tried to emulate (so I'm not sure if it would try to emulate
kernel instructions). And it wouldn't emulate that instruction, my program
died with SIGILL, but obviously it still needs to load it to see what kind
of instruction it was.

johannes