Messages in this thread | | | Date | Wed, 4 Nov 2020 16:29:18 +0000 | From | Mark Rutland <> | Subject | Re: entry: Fix the incorrect ordering of lockdep and RCU check |
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On Wed, Nov 04, 2020 at 02:06:23PM +0100, Thomas Gleixner wrote: > When an exception/interrupt hits kernel space and the kernel is not > currently in the idle task then RCU must be watching. > > irqentry_enter() validates this via rcu_irq_enter_check_tick(), which in > turn invokes lockdep when taking a lock. But at that point lockdep does not > yet know about the fact that interrupts have been disabled by the CPU, > which triggers a lockdep splat complaining about inconsistent state. > > Invoking trace_hardirqs_off() before rcu_irq_enter_check_tick() defeats the > point of rcu_irq_enter_check_tick() because trace_hardirqs_off() uses RCU. > > So use the same sequence as for the idle case and tell lockdep about the > irq state change first, invoke the RCU check and then do the lockdep and > tracer update. > > Fixes: a5497bab5f72 ("entry: Provide generic interrupt entry/exit code") > Reported-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Cc: stable@vger.kernel.org
I just gave this a spin on x86_64 defconfig + PROVE_LOCKING + DEBUG_LOCKDEP + NO_HZ_FULL + CONTEXT_TRACKING_FORCE, and it gets rid of the boot-time splat. So FWIW:
Tested-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> --- > kernel/entry/common.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- a/kernel/entry/common.c > +++ b/kernel/entry/common.c > @@ -337,10 +337,10 @@ noinstr irqentry_state_t irqentry_enter( > * already contains a warning when RCU is not watching, so no point > * in having another one here. > */ > + lockdep_hardirqs_off(CALLER_ADDR0); > instrumentation_begin(); > rcu_irq_enter_check_tick(); > - /* Use the combo lockdep/tracing function */ > - trace_hardirqs_off(); > + trace_hardirqs_off_finish(); > instrumentation_end(); > > return ret;
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