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Message-ID: <20070918212105.GL8665@linux.vnet.ibm.com>
Date: Tue, 18 Sep 2007 14:21:05 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Nadia Derbey <Nadia.Derbey@...l.net>,
Alexey Dobriyan <adobriyan@...ru>,
linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 2/2] lockdep: rcu_dereference() vs rcu_read_lock()
On Tue, Sep 18, 2007 at 10:27:01PM +0200, Peter Zijlstra wrote:
>
>
> warn when rcu_dereference() is used outside of rcu_read_lock()
Cool!!!
> [ generates a _lot_ of output when booted ]
I bet! If you create an annotation for rcu_read_lock_bh()
and rcu_read_unlock_bh() like you did for rcu_read_lock() and
rcu_read_unlock(), I suspect that much of the noise will go away.
Of course, preempt_disable() / preempt_enable() is a bit of a two-edged
sword here. It is OK to do rcu_dereference() under explicit
preempt_disable(), but not OK under the implicit preempt_disable()
implied by spin_lock() in CONFIG_PREEMPT. One way to handle this
would be to have _rcu() wrappers for preempt_disable() and
preempt_enable() that are annotated.
There is probably a better way... Can't think of one right off, though...
Thanx, Paul
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> include/linux/lockdep.h | 3 ++
> include/linux/rcupdate.h | 5 ++++
> kernel/lockdep.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 61 insertions(+)
>
> Index: linux-2.6/include/linux/lockdep.h
> ===================================================================
> --- linux-2.6.orig/include/linux/lockdep.h
> +++ linux-2.6/include/linux/lockdep.h
> @@ -303,6 +303,8 @@ extern void lock_acquire(struct lockdep_
> extern void lock_release(struct lockdep_map *lock, int nested,
> unsigned long ip);
>
> +extern int lock_is_held(struct lockdep_map *lock);
> +
> # define INIT_LOCKDEP .lockdep_recursion = 0,
>
> #define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)
> @@ -319,6 +321,7 @@ static inline void lockdep_on(void)
>
> # define lock_acquire(l, s, t, r, c, i) do { } while (0)
> # define lock_release(l, n, i) do { } while (0)
> +# define lock_is_held(l) (0)
> # define lockdep_init() do { } while (0)
> # define lockdep_info() do { } while (0)
> # define lockdep_init_map(lock, name, key, sub) do { (void)(key); } while (0)
> Index: linux-2.6/include/linux/rcupdate.h
> ===================================================================
> --- linux-2.6.orig/include/linux/rcupdate.h
> +++ linux-2.6/include/linux/rcupdate.h
> @@ -138,9 +138,11 @@ extern int rcu_needs_cpu(int cpu);
> 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_)
> +# define rcu_read_held() WARN_ON_ONCE(!lock_is_held(&rcu_lock_map))
> #else
> # define rcu_read_acquire() do { } while (0)
> # define rcu_read_release() do { } while (0)
> +# define rcu_read_held() do { } while (0)
> #endif
>
> /**
> @@ -216,6 +218,7 @@ extern struct lockdep_map rcu_lock_map;
> do { \
> local_bh_disable(); \
> __acquire(RCU_BH); \
> + rcu_read_acquire(); \
> } while(0)
>
> /*
> @@ -225,6 +228,7 @@ extern struct lockdep_map rcu_lock_map;
> */
> #define rcu_read_unlock_bh() \
> do { \
> + rcu_read_release(); \
> __release(RCU_BH); \
> local_bh_enable(); \
> } while(0)
> @@ -254,6 +258,7 @@ extern struct lockdep_map rcu_lock_map;
> #define rcu_dereference(p) ({ \
> typeof(p) _________p1 = ACCESS_ONCE(p); \
> smp_read_barrier_depends(); \
> + rcu_read_held(); \
> (_________p1); \
> })
>
> Index: linux-2.6/kernel/lockdep.c
> ===================================================================
> --- linux-2.6.orig/kernel/lockdep.c
> +++ linux-2.6/kernel/lockdep.c
> @@ -2624,6 +2624,36 @@ static int lock_release_nested(struct ta
> return 1;
> }
>
> +static int __lock_is_held(struct lockdep_map *lock)
> +{
> + struct task_struct *curr = current;
> + struct held_lock *hlock, *prev_hlock;
> + unsigned int depth;
> + int i;
> +
> + /*
> + * Check whether the lock exists in the current stack
> + * of held locks:
> + */
> + depth = curr->lockdep_depth;
> + if (DEBUG_LOCKS_WARN_ON(!depth))
> + return 0;
> +
> + prev_hlock = NULL;
> + for (i = depth-1; i >= 0; i--) {
> + hlock = curr->held_locks + i;
> + /*
> + * We must not cross into another context:
> + */
> + if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
> + break;
> + if (hlock->instance == lock)
> + return 1;
> + prev_hlock = hlock;
> + }
> + return 0;
> +}
> +
> /*
> * Remove the lock to the list of currently held locks - this gets
> * called on mutex_unlock()/spin_unlock*() (or on a failed
> @@ -2727,6 +2757,29 @@ void lock_release(struct lockdep_map *lo
>
> EXPORT_SYMBOL_GPL(lock_release);
>
> +int lock_is_held(struct lockdep_map *lock)
> +{
> + int ret = 0;
> + unsigned long flags;
> +
> + if (unlikely(!lock_stat && !prove_locking))
> + return 0;
> +
> + if (unlikely(current->lockdep_recursion))
> + return -EBUSY;
> +
> + raw_local_irq_save(flags);
> + check_flags(flags);
> + current->lockdep_recursion = 1;
> + ret = __lock_is_held(lock);
> + current->lockdep_recursion = 0;
> + raw_local_irq_restore(flags);
> +
> + return ret;
> +}
> +
> +EXPORT_SYMBOL_GPL(lock_is_held);
> +
> #ifdef CONFIG_LOCK_STAT
> static int
> print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
-
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