Messages in this thread | | | Date | Tue, 1 Dec 2020 20:14:41 +0100 | From | Peter Zijlstra <> | Subject | Re: [GIT pull] locking/urgent for v5.10-rc6 |
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On Tue, Dec 01, 2020 at 06:57:37PM +0000, Mark Rutland wrote: > On Tue, Dec 01, 2020 at 07:15:06PM +0100, Peter Zijlstra wrote: > > On Tue, Dec 01, 2020 at 03:55:19PM +0100, Peter Zijlstra wrote: > > > On Tue, Dec 01, 2020 at 06:46:44AM -0800, Paul E. McKenney wrote: > > > > > > > > So after having talked to Sven a bit, the thing that is happening, is > > > > > that this is the one place where we take interrupts with RCU being > > > > > disabled. Normally RCU is watching and all is well, except during idle. > > > > > > > > Isn't interrupt entry supposed to invoke rcu_irq_enter() at some point? > > > > Or did this fall victim to recent optimizations? > > > > > > It does, but the problem is that s390 is still using > > > > I might've been too quick there, I can't actually seem to find where > > s390 does rcu_irq_enter()/exit(). > > > > Also, I'm thinking the below might just about solve the current problem. > > The next problem would then be it calling TRACE_IRQS_ON after it did > > rcu_irq_exit()... :/ > > I gave this patch a go under QEMU TCG atop v5.10-rc6 s390 defconfig with > PROVE_LOCKING and DEBUG_ATOMIC_SLEEP. It significantly reduces the > number of lockdep splats, but IIUC we need to handle the io_int_handler > path in addition to the ext_int_handler path, and there's a remaining > lockdep splat (below).
I'm amazed it didn't actually make things worse, given how I failed to spot do_IRQ() was arch code etc..
> If this ends up looking like we'll need more point-fixes, I wonder if we > should conditionalise the new behaviour of the core idle code under a > new CONFIG symbol for now, and opt-in x86 and arm64, then transition the > rest once they've had a chance to test. They'll still be broken in the > mean time, but no more so than they previously were.
We can do that I suppose... :/
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