Messages in this thread Patch in this message | | | From | Neeraj Upadhyay <> | Subject | [PATCH] rcu: Fix dynticks_nmi_nesting underflow check in rcu_is_cpu_rrupt_from_idle | Date | Wed, 23 Dec 2020 14:09:37 +0530 |
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For the smp_call_function() optimization, where callbacks can run from idle context, in commit 806f04e9fd2c ("rcu: Allow for smp_call_function() running callbacks from idle"), an additional check is added in rcu_is_cpu_rrupt_from_idle(), for dynticks_nmi_nesting value being 0, for these smp_call_function() callbacks running from idle loop. However, this commit missed updating a preexisting underflow check of dynticks_nmi_nesting, which checks for a non zero positive value. Fix this warning and while at it, read the counter only once.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> ---
Hi,
I was not able to get this warning, with scftorture.
RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0, "RCU dynticks_nmi_nesting counter underflow/zero!");
Not sure if idle loop smp_call_function() optimization is already present in mainline?
Another thing, which I am not sure of is, maybe lockdep gets disabled in the idle loop contexts, where rcu_is_cpu_rrupt_from_idle() is called? Was this the original intention, to keep the lockdep based RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0 check separate from idle task context nesting value WARN_ON_ONCE(!nesting && !is_idle_task(current)) check?
Thanks Neeraj
kernel/rcu/tree.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index bc8b489..c3037cf 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -457,11 +457,10 @@ static int rcu_is_cpu_rrupt_from_idle(void) /* Check for counter underflows */ RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0, "RCU dynticks_nesting counter underflow!"); - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0, - "RCU dynticks_nmi_nesting counter underflow/zero!"); + nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting); + RCU_LOCKDEP_WARN(nesting < 0, "RCU dynticks_nmi_nesting counter underflow!"); /* Are we at first interrupt nesting level? */ - nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting); if (nesting > 1) return false; -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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