RE: [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Luck, Tony
> Sent: 13 June 2022 17:27
> 
> >> It's listed in Documentation/atomic_bitops.txt.
> >
> > Oh, so my memory was actually correct that I saw it in the docs
> > somewhere.
> > WDYT, should I mention this here in the code (block comment) as well
> > that it's atomic and must not lose `volatile` as Andy suggested or
> > it's sufficient to have it in the docs (+ it's not underscored)?
> 
> I think a comment that the "volatile" is required to prevent re-ordering
> is enough.
> 
> But maybe others are sufficiently clear on the meaning? I once wasted
> time looking for the non-atomic __test_bit() version (to use in some code
> that was already protected by a spin lock, so didn't need the overhead
> of an "atomic" version) before realizing there wasn't a non-atomic one.

Does it make any sense for 'test bit' to be atomic?

I'm not even sure is needs any ordering constraints either.
The result is always stale - the value can be changed by
another cpu at any time.

The set/clear atomic bit-ops require a RMW bus cycle - which has
to be locked (or similar) to avoid corruption.

The atomic 'test and set' (etc) are RMW and return a valid state.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)




[Index of Archives]     [Netdev]     [Linux Wireless]     [Kernel Newbies]     [Security]     [Linux for Hams]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]

  Powered by Linux