Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 13 Jan 2020 14:03:41 +0100 | Subject | Re: [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen |
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On Fri, Jan 10, 2020 at 9:15 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Fri, Jan 10, 2020 at 11:47 AM Arnd Bergmann <arnd@arndb.de> wrote: > > > > Isn't the read_barrier_depends() the only reason for actually needing > > the temporary local variable that must not be volatile? > > > > If you make alpha provide its own READ_ONCE() as the first > > step, it would seem that the rest of the series gets much easier > > as the others can go back to the simple statement from your > > Hmm.. The union still would cause that "take the address of a volatile > thing on the stack" problem, wouldn't it? And that was what caused > most of the issues.
Ah, I was missing that there is still the union in smp_load_acquire(), I only saw that the one in READ_ONCE() is needed only on alpha.
The number of files using smp_load_acquire() is fairly small though, so we could consider changing it to pass both source and destination as macro arguments and use typeof(dest) instad of typeof(source) to avoid the volatile pointer access.
> I think the _real_ issue is how KASAN forces that odd pair of inline > functions in order to have the annotations on the accesses.
But the inline functions (I assume you mean __write_once_size and __read_once_size_nocheck?) are completely removed after Will's series, so those no longer cause harm, right?
Arnd
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