On Wed, May 24, 2023, Peter Zijlstra wrote:
> On Wed, May 24, 2023 at 01:16:03PM -0700, Sean Christopherson wrote:
> > Of course, the only accesses outside of mmu_lock are reads, so on x86 that
> > "atomic" access is just a READ_ONCE() load, but that's not the case for all
> > architectures.
>
> This is true on *all* archs. atomic_set() and atomic_read() are no more
> and no less than WRITE_ONCE() / READ_ONCE().
Ah, I take it s390's handcoded assembly routines are just a paranoid equivalents
and not truly special? "l" and "st" do sound quite generic...
commit 7657e41a0bd16c9d8b3cefe8fd5d6ac3c25ae4bf
Author: Heiko Carstens <hca@xxxxxxxxxxxxx>
Date: Thu Feb 17 13:13:58 2011 +0100
[S390] atomic: use inline asm
Use inline assemblies for atomic_read/set(). This way there shouldn't
be any questions or subtle volatile semantics left.
static inline int __atomic_read(const atomic_t *v)
{
int c;
asm volatile(
" l %0,%1\n"
: "=d" (c) : "R" (v->counter));
return c;
}
static inline void __atomic_set(atomic_t *v, int i)
{
asm volatile(
" st %1,%0\n"
: "=R" (v->counter) : "d" (i));
}
