On 2019-10-16, Tejun Heo tj@kernel.org wrote:
Hello, Aleksa.
On Wed, Oct 16, 2019 at 07:32:19PM +1100, Aleksa Sarai wrote:
Maybe I'm misunderstanding Documentation/atomic_t.txt, but it looks to me like it's explicitly saying that I shouldn't use atomic64_t if I'm just using it for fetching and assignment.
Hah, where is it saying that?
Isn't that what this says:
Therefore, if you find yourself only using the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all and are doing it wrong.
Doesn't using just atomic64_read() and atomic64_set() fall under "only using the non-RMW operations of atomic_t"? But yes, I agree that any locking is overkill.
As for 64-bit on 32-bit machines -- that is a separate issue, but from [1] it seems to me like there are more problems that *_ONCE() fixes than just split reads and writes.
Your explanations are too wishy washy. If you wanna fix it, please do it correctly. R/W ONCE isn't the right solution here.
Sure, I will switch it to use atomic64_read() and atomic64_set() instead if that's what you'd prefer. Though I will mention that on quite a few architectures atomic64_read() is defined as:
#define atomic64_read(v) READ_ONCE((v)->counter)