Paul E. McKenney wrote:
> On Tue, Apr 13, 2010 at 05:13:06PM -0700, David Miller wrote:
>> From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
>> Date: Wed, 14 Apr 2010 02:02:27 +0200
>>
>>> I just have a guess though....
>>> This seems to always happen from NMI path, and lockdep is disabled on NMI.
>>> I suspect the lock_acquire() performed by rcu_read_lock() is just ignored
>>> and then the rcu_read_lock_held() check has the wrong result...
>> Yeah, I bet that's it too.
>>
>> lock_is_held() can't return anything meaningful while lockdep is
>> disabled, which it is during NMIs.
>
> Ah! So I just need to add a "current->lockdep_recursion"
> check to debug_lockdep_rcu_enabled(). And move the function to
> kernel/rcutree_plugin.h to avoid #include hell.
>
> See below for (untested) patch.
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> include/linux/rcupdate.h | 5 +----
> kernel/rcutree_plugin.h | 11 +++++++++++
> 2 files changed, 12 insertions(+), 4 deletions(-)
>
> commit 304d8da6cd791a81ce3164f867e1b3ef4f9af1d1
> Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Date: Tue Apr 13 18:45:51 2010 -0700
>
> rcu: Make RCU lockdep check the lockdep_recursion variable
>
> The lockdep facility temporarily disables lockdep checking by incrementing
> the current->lockdep_recursion variable. Such disabling happens in NMIs
> and in other situations where lockdep might expect to recurse on itself.
> This patch therefore checks current->lockdep_recursion, disabling RCU
> lockdep splats when this variable is non-zero.
>
> Reported-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Reported-by: David Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 9f1ddfe..07db2fe 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -101,10 +101,7 @@ extern struct lockdep_map rcu_sched_lock_map;
> # define rcu_read_release_sched() \
> lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
>
> -static inline int debug_lockdep_rcu_enabled(void)
> -{
> - return likely(rcu_scheduler_active && debug_locks);
> -}
> +extern int debug_lockdep_rcu_enabled(void);
>
> /**
> * rcu_read_lock_held - might we be in RCU read-side critical section?
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index 79b53bd..2169abe 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -1067,3 +1067,14 @@ static void rcu_needs_cpu_flush(void)
> }
>
> #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +
> +int debug_lockdep_rcu_enabled(void)
> +{
> + return likely(rcu_scheduler_active &&
> + debug_locks &&
> + current->lockdep_recursion == 0);
> +}
> +
Looks good to me too, but I think
'likely' is needless since the function is not inline.
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