Re: [PATCH v7 1/4] qrwlock: A queue read/write lock implementation

[Andi Kleen]

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:
>
> In this case, we seem to want the xadd() semantics. I guess we can use
> "atomic_add_return(val,&atomic)-val" and just assume that the compiler
> gets it right (with the addition and the subtraction cancelling out).

It can't, as we use inline assembler. 

In theory it could with __sync_* or __atomic_* intrinsics but we
traditionally don't use them as they don't support patchable LOCK

(maybe it would be time to get rid of the patchable LOCK though?)

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only
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