RE: [RFC PATCH v2 2/6] PM / Runtime: introduce pm_runtime_set_memalloc_noio()

[David Laight]

> Looks the problem is worse than above, not only bitfields are affected, the
> adjacent fields might be involved too, see:
> 
>            http://lwn.net/Articles/478657/

Not mentioned in there is that even with x86/amd64 given
a struct with the following adjacent fields:
	char a;
	char b;
	char c;
then foo->b |= 0x80; might do a 32bit RMW cycle.
This will (well might - but probably does) happen
if compiled to a 'BTS' instruction.
The x86 instruction set docs are actually unclear
as to whether the 32bit cycle might even be misaligned!
amd64 might do a 64bit cycle (not checked the docs).

	David



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