Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 15 May 2018 09:55:13 -0700 | Subject | Re: [PATCH] vsprintf: Fix memory barriers of ptr_key to have_filed_random_ptr_key |
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On Tue, May 15, 2018 at 7:06 AM Steven Rostedt <rostedt@goodmis.org> wrote: > - smp_mb(); > + smp_wmb(); > WRITE_ONCE(have_filled_random_ptr_key, true);
> + /* Read ptr_key after reading have_filled_random_ptr_key */ > + smp_rmb(); > + > #ifdef CONFIG_64BIT > hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
Hmm. smp_wmb/rmb are basically free on x86, but on some architectures smp_rmb() in particular can be pretty expensive.
So when you have a "handoff" situation like this, it's _probably_ better to use use "smp_store_release()" and "smp_load_acquire()". To some degree that might also be better for documentation purposes, because that's exactly the "release-acquire" pattern.
That said, I'm not convinced this really matters all that much for a boot-time flag like this. The race is pretty theoretical.
Linus
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