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However, some callbacks may also > > > > be invoked from an unlocked context, where no rq is locked and in this case > > > > rq should be NULL. > > > > > > > > In the latter case, it's acceptable for preemption to remain enabled, but > > > > we still want to explicitly set locked_rq = NULL. If during the execution > > > > of the callback we jump on another CPU, it'd still be in an unlocked state, > > > > so it's locked_rq is still NULL. > > > > > > Right; but doing superfluous NULL stores seems pointless. So better to > > > avoid the store entirely, rather than making it more expensive and no > > > less pointless, right? > > > > Right, we can definitely avoid rewriting NULL. > > The following should do the trick. > > > > Breno, can you give it a try? > > Sure thing. I've tested it and I don't see the warning on my side. > > Would you like to me post the patch, probably removing the WARN_ONCE() > as raised by peterz? Sure, go ahead. Yes, let's remove the WARN_ON_ONCE(). And thanks Peter for all the suggestions! -Andrea