Re: [PATCH 7/7] microblaze: Do atomic operations by using exclusive ops

[Peter Zijlstra]

On Thu, Feb 13, 2020 at 09:58:49AM +0100, Peter Zijlstra wrote:

> The thing is, your bog standard LL/SC _SHOULD_ fail the SC if someone
> else does a regular store to the same variable. See the example in
> Documentation/atomic_t.txt.
> 
> That is, a competing SW/SWI should result in the interconnect responding
> with something other than EXOKAY, the SWX should fail and MSR[C] <- 1.

The thing is; we have code that relies on this behaviour. There are a
few crusty SMP archs that sorta-kinda limp along (mostly by disabling
some of the code and praying the rest doesn't trigger too often), but we
really should not allow more broken SMP archs.