Re: [patch 6/11] s390: in_interrupt vs. in_atomic.

[Andrew Morton <akpm@osdl.org>]

Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:
>
> [patch 6/11] s390: in_interrupt vs. in_atomic.
> 
> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
> 
> The condition for no context in do_exception checks for hard and
> soft interrupts by using in_interrupt() but not for preemption.
> This is bad for the users of __copy_from/to_user_inatomic because
> the fault handler might call schedule although the preemption
> count is != 0. Use in_atomic() instead in_interrupt().
> 

hm.  Under what circumstances do you expect this test to trigger?

We have the in_atomic() test in x86's do_page_fault() because as a
super-special case, kmap_atomic() will increment preempt_count() even if
!CONFIG_PREEMPT.  This is how x86 handles faults during
pagecache<->userspace copies into a kmap_atomically-mapped page.  s390
doesn't do any of that.

So.  What's going on in here?

> 
> diffstat:
>  arch/s390/mm/fault.c |    2 +-
>  1 files changed, 1 insertion(+), 1 deletion(-)
> 
> diff -urpN linux-2.6/arch/s390/mm/fault.c linux-2.6-patched/arch/s390/mm/fault.c
> --- linux-2.6/arch/s390/mm/fault.c	2005-06-01 19:42:54.000000000 +0200
> +++ linux-2.6-patched/arch/s390/mm/fault.c	2005-06-01 19:43:18.000000000 +0200
> @@ -207,7 +207,7 @@ do_exception(struct pt_regs *regs, unsig
>  	 * we are not in an interrupt and that there is a 
>  	 * user context.
>  	 */

Comment needs updating...

> -        if (user_address == 0 || in_interrupt() || !mm)
> +        if (user_address == 0 || in_atomic() || !mm)
>                  goto no_context;
>  
>  	/*