Messages in this thread | | | Date | Mon, 26 Oct 2020 21:35:01 +0100 | From | David Sterba <> | Subject | Re: possible lockdep regression introduced by 4d004099a668 ("lockdep: Fix lockdep recursion") |
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On Mon, Oct 26, 2020 at 01:55:24PM +0100, Peter Zijlstra wrote: > On Mon, Oct 26, 2020 at 11:56:03AM +0000, Filipe Manana wrote: > > > That smells like the same issue reported here: > > > > > > https://lkml.kernel.org/r/20201022111700.GZ2651@hirez.programming.kicks-ass.net > > > > > > Make sure you have commit: > > > > > > f8e48a3dca06 ("lockdep: Fix preemption WARN for spurious IRQ-enable") > > > > > > (in Linus' tree by now) and do you have CONFIG_DEBUG_PREEMPT enabled? > > > > Yes, CONFIG_DEBUG_PREEMPT is enabled. > > Bummer :/
My builds don't have that enabled (CONFIG_PREEMPT_NONE=y) but I still see the warning (same scenario as for Filipe). That is with today's master branch + your fix from locking/urgent.
> > I'll try with that commit and let you know, however it's gonna take a > > few hours to build a kernel and run all fstests (on that test box it > > takes over 3 hours) to confirm that fixes the issue. > > *ouch*, 3 hours is painful. How long to make it sick with the current > kernel? quicker I would hope? > > > Thanks for the quick reply! > > Anyway, I don't think that commit can actually explain the issue :/ > > The false positive on lockdep_assert_held() happens when the recursion > count is !0, however we _should_ be having IRQs disabled when > lockdep_recursion > 0, so that should never be observable. > > My hope was that DEBUG_PREEMPT would trigger on one of the > __this_cpu_{inc,dec}(lockdep_recursion) instance, because that would > then be a clear violation.
I can start another round (in my case it's more than 4 hours to reproduce it) with DEBUG_PREEMPT, unless you have something else to test.
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