Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

From: Peter Zijlstra
Date: Tue Aug 20 2019 - 09:56:33 EST

On Sat, Aug 17, 2019 at 01:08:02AM -0700, Linus Torvalds wrote:

> The data tearing issue is almost a non-issue. We're not going to add
> WRITE_ONCE() to these kinds of places for no good reason.

Paulmck actually has an example of that somewhere; ISTR that particular
case actually got fixed by GCC, but I'd really _love_ for some compiler
people (both GCC and LLVM) to state that their respective compilers will
not do load/store tearing for machine word sized load/stores.

Without this written guarantee (which supposedly was in older GCC
manuals but has since gone missing), I'm loathe to rely on it.

Yes, it is very rare, but it is a massive royal pain to debug if/when it
does do happen.