Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 6 Mar 2023 09:47:34 -0800 | Subject | Re: [PATCH 5/5] cpumask: fix comment of cpumask_xxx |
| |
On Mon, Mar 6, 2023 at 9:29 AM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > The correct thing to do is always that > > * Returns >= nr_cpu_ids if no cpus set. > > because nr_cpu_ids is always the *smallest* of the access sizes. > > Of course, right now Guenter seems to be reporting a problem with that > optimization, so unless I figure out what is going on I'll just need > to revert it anyway.
Ahh. And the reason is exactly that people do *not* follow that "Returns >= nr_cpu_ids" rule.
The drivers/char/random.c code is very wrong, and does
if (cpu == nr_cpumask_bits) cpu = cpumask_first(&timer_cpus);
which fails miserably exactly because it doesn't use ">=".
Oh well.
I'll have to look for more of this pattern, but basically all those "xyz_cpumask_bits" things were supposed to always be just internal to that header file implementation, which is *exactly* why you have to check the result for ">= nr_cpu_ids".
Linus
| |