Messages in this thread | | | Date | Mon, 21 Jun 2021 09:28:02 +0200 | From | Peter Zijlstra <> | Subject | Re: RCU vs data_race() |
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On Sun, Jun 20, 2021 at 02:01:27PM -0700, Paul E. McKenney wrote: > On Sun, Jun 20, 2021 at 09:14:28PM +0200, Peter Zijlstra wrote:
> > I don't buy that argument. pr_err() (or worse) is not supposed to > > happen, ever. If it does, *that* is a far worse condition that any data > > race possibly found by kcsan. > > > > So the only way the pr_err() expression itself can lead to kcsan > > determining a data-race, if something far worse triggered the pr_err() > > itself. > > Earlier, you said pr_warn(). Above, I said pr_*(). Now you say > pr_err(). But OK...
Same, thing.. also Sundays aren't great for details it seems :-)
> Let's take for example the pr_err() in __call_rcu(), that is, the > double-free diagnostic. A KCSAN warning on the unmarked load from > head->func could give valuable information on the whereabouts of the > other code interfering with the callback. Blanket disabling of KCSAN > across all pr_err() calls (let alone all pr_*() calls) would be the > opposite of helpful.
I'm confused. That pr_err() should never happen in a correct program. If it happens, fix it and any data race as a consequence of that pr_err() no longer exists either.
I fundementally don't see the relevance of a possible data race from a statement that should never happen in a correct program to begin with.
Why do you think otherwise?
> > You've lost me on the schedule thing, what? > > The definition of schedule_timeout_interruptible() is in part of the > kernel that uses much looser KCSAN checking. Thus there are some > KCSAN warnings from RCU involving schedule_timeout_interruptible(). > But at least some of these warnings are for conflicting writes, which > many parts of the kernel suppress KCSAN warnings for.
You've lost me again.. schedule_timeout_interruptible() doesn't do writes to rcu state, does it? So how can there be problems?
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