Messages in this thread Patch in this message | | | Date | Thu, 19 Nov 2020 13:35:12 -0800 | From | "Paul E. McKenney" <> | Subject | Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...) |
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On Thu, Nov 19, 2020 at 08:38:19PM +0100, Marco Elver wrote: > On Thu, Nov 19, 2020 at 10:48AM -0800, Paul E. McKenney wrote: > > On Thu, Nov 19, 2020 at 06:02:59PM +0100, Marco Elver wrote:
[ . . . ]
> > > I can try bisection again, or reverting some commits that might be > > > suspicious? But we'd need some selection of suspicious commits. > > > > The report claims that one of the rcu_node ->lock fields is held > > with interrupts enabled, which would indeed be bad. Except that all > > of the stack traces that it shows have these locks held within the > > scheduling-clock interrupt handler. Now with the "rcu: Don't invoke > > try_invoke_on_locked_down_task() with irqs disabled" but without the > > "sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled" > > commit, I understand why. With both, I don't see how this happens. > > I'm at a loss, but happy to keep bisecting and trying patches. I'm also > considering: > > Is it the compiler? Probably not, I tried 2 versions of GCC. > > Can we trust lockdep to precisely know IRQ state? I know there's > been some recent work around this, but hopefully we're not > affected here? > > Is QEMU buggy? > > > At this point, I am reduced to adding lockdep_assert_irqs_disabled() > > calls at various points in that code, as shown in the patch below. > > > > At this point, I would guess that your first priority would be the > > initial bug rather than this following issue, but you never know, this > > might well help diagnose the initial bug. > > I don't mind either way. I'm worried deadlocking the whole system might > be worse.
Here is another set of lockdep_assert_irqs_disabled() calls on the off-chance that they actually find something.
Thanx, Paul
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commit bcca5277df3f24db15e15ccc8b05ecf346d05169 Author: Paul E. McKenney <paulmck@kernel.org> Date: Thu Nov 19 13:30:33 2020 -0800
rcu: Add lockdep_assert_irqs_disabled() to raw_spin_unlock_rcu_node() macros This commit adds a lockdep_assert_irqs_disabled() call to the helper macros that release the rcu_node structure's ->lock, namely to raw_spin_unlock_rcu_node(), raw_spin_unlock_irq_rcu_node() and raw_spin_unlock_irqrestore_rcu_node(). The point of this is to help track down a situation where lockdep appears to be insisting that interrupts are enabled while holding an rcu_node structure's ->lock. Link: https://lore.kernel.org/lkml/20201111133813.GA81547@elver.google.com/ Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 59ef1ae..bf0827d 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -378,7 +378,11 @@ do { \ smp_mb__after_unlock_lock(); \ } while (0) -#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock)) +#define raw_spin_unlock_rcu_node(p) \ +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irq_rcu_node(p) \ do { \ @@ -387,7 +391,10 @@ do { \ } while (0) #define raw_spin_unlock_irq_rcu_node(p) \ - raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irqsave_rcu_node(p, flags) \ do { \ @@ -396,7 +403,10 @@ do { \ } while (0) #define raw_spin_unlock_irqrestore_rcu_node(p, flags) \ - raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags); \ +} while (0) #define raw_spin_trylock_rcu_node(p) \ ({ \
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