On 2019-10-17, Aleksa Sarai <cyphar@xxxxxxxxxx> wrote: > On 2019-10-16, Tejun Heo <tj@xxxxxxxxxx> 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) Though I guess that's because on those architectures it turns out that READ_ONCE is properly atomic? -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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