On Thu, Aug 16, 2007 at 04:25:07PM +0200, Peter Zijlstra wrote:
>
> There seem to be some unbalanced rcu_read_{,un}lock() issues of late,
> how about doing something like this:
This will break when rcu_read_lock() and rcu_read_unlock() are invoked
from NMI/SMI handlers -- the raw_local_irq_save() in lock_acquire() will
not mask NMIs or SMIs.
One approach would be to check for being in an NMI/SMI handler, and
to avoid calling lock_acquire() and lock_release() in those cases.
Another approach would be to use sparse, which has checks for
rcu_read_lock()/rcu_read_unlock() nesting.
Thanx, Paul
> Signed-off-by: Peter Zijlstra <[email protected]>
> ---
> include/linux/lockdep.h | 7 +++++++
> include/linux/rcupdate.h | 12 ++++++++++++
> kernel/rcupdate.c | 8 ++++++++
> 3 files changed, 27 insertions(+)
>
> Index: linux-2.6/include/linux/lockdep.h
> ===================================================================
> --- linux-2.6.orig/include/linux/lockdep.h
> +++ linux-2.6/include/linux/lockdep.h
> @@ -252,6 +252,13 @@ extern void lockdep_init_map(struct lock
> struct lock_class_key *key, int subclass);
>
> /*
> + * To initialize a lockdep_map statically use this macro.
> + * Note that _name must not be NULL.
> + */
> +#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
> + { .name = (_name), .key = (void *)(_key), }
> +
> +/*
> * Reinitialize a lock key - for cases where there is special locking or
> * special initialization of locks so that the validator gets the scope
> * of dependencies wrong: they are either too broad (they need a class-split)
> Index: linux-2.6/include/linux/rcupdate.h
> ===================================================================
> --- linux-2.6.orig/include/linux/rcupdate.h
> +++ linux-2.6/include/linux/rcupdate.h
> @@ -41,6 +41,7 @@
> #include <linux/percpu.h>
> #include <linux/cpumask.h>
> #include <linux/seqlock.h>
> +#include <linux/lockdep.h>
>
> /**
> * struct rcu_head - callback structure for use with RCU
> @@ -133,6 +134,15 @@ static inline void rcu_bh_qsctr_inc(int
> extern int rcu_pending(int cpu);
> extern int rcu_needs_cpu(int cpu);
>
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +extern struct lockdep_map rcu_lock_map;
> +# define rcu_read_acquire() lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
> +# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
> +#else
> +# define rcu_read_acquire() do { } while (0)
> +# define rcu_read_release() do { } while (0)
> +#endif
> +
> /**
> * rcu_read_lock - mark the beginning of an RCU read-side critical section.
> *
> @@ -166,6 +176,7 @@ extern int rcu_needs_cpu(int cpu);
> do { \
> preempt_disable(); \
> __acquire(RCU); \
> + rcu_read_acquire(); \
> } while(0)
>
> /**
> @@ -175,6 +186,7 @@ extern int rcu_needs_cpu(int cpu);
> */
> #define rcu_read_unlock() \
> do { \
> + rcu_read_release(); \
> __release(RCU); \
> preempt_enable(); \
> } while(0)
> Index: linux-2.6/kernel/rcupdate.c
> ===================================================================
> --- linux-2.6.orig/kernel/rcupdate.c
> +++ linux-2.6/kernel/rcupdate.c
> @@ -49,6 +49,14 @@
> #include <linux/cpu.h>
> #include <linux/mutex.h>
>
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +static struct lock_class_key rcu_lock_key;
> +struct lockdep_map rcu_lock_map =
> + STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
> +
> +EXPORT_SYMBOL_GPL(rcu_lock_map);
> +#endif
> +
> /* Definition for rcupdate control block. */
> static struct rcu_ctrlblk rcu_ctrlblk = {
> .cur = -300,
>
>
> -
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