Re: [PATCH v2 4/4] lib/vsprintf: Always check interrupt context restrictions

[Thomas Weißschuh]

On Mon, May 04, 2026 at 03:00:44PM +0200, Peter Zijlstra wrote:
> On Mon, May 04, 2026 at 12:47:20PM +0200, Thomas Weißschuh wrote:
> > When kptr_restrict is set to '1' restricted pointers can not be used
> > in IRQ context. As kptr_restrict can change at any time at runtime,
> > this means that restricted pointers can not be used from IRQ context
> > in general.
> > 
> > Add some assertions to detect misuse early, independently of the
> > runtime configuration of the test system.
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> > ---
> >  lib/vsprintf.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 021db95087fe..185bd9e61144 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -871,6 +871,10 @@ char *restricted_pointer(char *buf, char *end, const void *ptr,
> >  
> >  	guard(lock_map_acquire)(&vsprintf_restricted_pointer_map);
> >  
> > +	lockdep_assert(!in_hardirq());
> > +	lockdep_assert(!in_serving_softirq());
> > +	lockdep_assert(!in_nmi());
> > +
> 
> did that want to be:
> 
> 	lockdep_assert(in_task());

Primarily it wants to be the inverse of the check further down the function:

	if (in_hardirq() || in_serving_softirq() || in_nmi()) {
		if (spec.field_width == -1)
			spec.field_width = 2 * sizeof(ptr);
		return error_string(buf, end, "pK-error", spec);


But in_task() looks like the better choice indeed, thanks!
I'll switch both locations to that for the next revision.

Unless Sebastian manages to get rid of it all, that is.


Thomas