Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 19 Oct 2023 11:22:38 -0700 | Subject | Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr() |
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On Thu, 19 Oct 2023 at 11:14, Peter Zijlstra <peterz@infradead.org> wrote: > > But are you really saying this_cpu_read() should not imply READ_ONCE()?
Well, Uros is saying that we may be *forced* to have that implication, much as I really hate it (and wonder at the competence of a compiler that forces the code-pessimizing 'volatile').
And the "it's not volatile" is actually our historical behavior. The volatile really is new, and didn't exist before your commit b59167ac7baf ("x86/percpu: Fix this_cpu_read()").
So the whole "implies READ_ONCE()" really seems to be due to that *one* mistake in our percpu sequence locking code.
Yes, it's been that way for 5 years now, but it was the other way around for the preceding decade....
Linus
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