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Date: Wed, 28 Jan 2009 09:20:15 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Johannes Berg <johannes@...solutions.net>
Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] timer: implement lockdep deadlock detection
On Tue, 2009-01-27 at 19:57 +0100, Johannes Berg wrote:
> This modifies the timer code in a way to allow lockdep to detect
> deadlocks resulting from a lock being taken in the timer function
> as well as around the del_timer_sync() call.
>
> Signed-off-by: Johannes Berg <johannes@...solutions.net>
Nice, thanks!
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> Ingo, do you want an incremental patch instead?
>
> v2: fix coding/comment style
> v3: accept freeing timer from timer function, fix init_timer_on_stack
> in no-lockdep case
>
> include/linux/timer.h | 103 ++++++++++++++++++++++++++++++++++++++++++--------
> kernel/timer.c | 70 ++++++++++++++++++++++++++++-----
> 2 files changed, 146 insertions(+), 27 deletions(-)
>
> --- wireless-testing.orig/include/linux/timer.h 2009-01-27 10:12:22.000000000 +0100
> +++ wireless-testing/include/linux/timer.h 2009-01-27 19:52:33.000000000 +0100
> @@ -21,52 +21,125 @@ struct timer_list {
> char start_comm[16];
> int start_pid;
> #endif
> +#ifdef CONFIG_LOCKDEP
> + struct lockdep_map lockdep_map;
> +#endif
> };
>
> extern struct tvec_base boot_tvec_bases;
>
> -#define TIMER_INITIALIZER(_function, _expires, _data) { \
> - .entry = { .prev = TIMER_ENTRY_STATIC }, \
> - .function = (_function), \
> - .expires = (_expires), \
> - .data = (_data), \
> - .base = &boot_tvec_bases, \
> +#ifdef CONFIG_LOCKDEP
> +/*
> + * NB: because we have to copy the lockdep_map, setting _key
> + * here is required, otherwise it could get initialised to the
> + * copy of the lockdep_map! We use the function pointer as the
> + * lockdep key here.
> + */
> +#define __TIMER_LOCKDEP_MAP_INITIALIZER(fn, name) \
> + .lockdep_map = STATIC_LOCKDEP_MAP_INIT(name, fn),
> +#else
> +#define __TIMER_LOCKDEP_MAP_INITIALIZER(fn, name)
> +#endif
> +
> +#define TIMER_INITIALIZER(_function, _expires, _data) { \
> + .entry = { .prev = TIMER_ENTRY_STATIC }, \
> + .function = (_function), \
> + .expires = (_expires), \
> + .data = (_data), \
> + .base = &boot_tvec_bases, \
> + __TIMER_LOCKDEP_MAP_INITIALIZER((_function), #_function)\
> }
>
> #define DEFINE_TIMER(_name, _function, _expires, _data) \
> struct timer_list _name = \
> TIMER_INITIALIZER(_function, _expires, _data)
>
> -void init_timer(struct timer_list *timer);
> -void init_timer_deferrable(struct timer_list *timer);
> +void init_timer_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key);
> +void init_timer_deferrable_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key);
> +
> +#ifdef CONFIG_LOCKDEP
> +#define init_timer(timer) \
> + do { \
> + static struct lock_class_key __key; \
> + init_timer_key((timer), #timer, &__key); \
> + } while (0)
> +
> +#define init_timer_deferrable(timer) \
> + do { \
> + static struct lock_class_key __key; \
> + init_timer_deferrable_key((timer), #timer, &__key); \
> + } while (0)
> +
> +#define init_timer_on_stack(timer) \
> + do { \
> + static struct lock_class_key __key; \
> + init_timer_on_stack_key((timer), #timer, &__key); \
> + } while (0)
> +
> +#define setup_timer(timer, fn, data) \
> + do { \
> + static struct lock_class_key __key; \
> + setup_timer_key((timer), #timer, &__key, (fn), (data));\
> + } while (0)
> +
> +#define setup_timer_on_stack(timer, fn, data) \
> + do { \
> + static struct lock_class_key __key; \
> + setup_timer_on_stack_key((timer), #timer, &__key, \
> + (fn), (data)); \
> + } while (0)
> +#else
> +#define init_timer(timer)\
> + init_timer_key((timer), NULL, NULL)
> +#define init_timer_deferrable(timer)\
> + init_timer_deferrable_key((timer), NULL, NULL)
> +#define init_timer_on_stack(timer)\
> + init_timer_on_stack_key((timer), NULL, NULL)
> +#define setup_timer(timer, fn, data)\
> + setup_timer_key((timer), NULL, NULL, (fn), (data))
> +#define setup_timer_on_stack(timer, fn, data)\
> + setup_timer_on_stack_key((timer), NULL, NULL, (fn), (data))
> +#endif
>
> #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
> -extern void init_timer_on_stack(struct timer_list *timer);
> +extern void init_timer_on_stack_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key);
> extern void destroy_timer_on_stack(struct timer_list *timer);
> #else
> static inline void destroy_timer_on_stack(struct timer_list *timer) { }
> -static inline void init_timer_on_stack(struct timer_list *timer)
> +static inline void init_timer_on_stack_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key)
> {
> - init_timer(timer);
> + init_timer_key(timer, name, key);
> }
> #endif
>
> -static inline void setup_timer(struct timer_list * timer,
> +static inline void setup_timer_key(struct timer_list * timer,
> + const char *name,
> + struct lock_class_key *key,
> void (*function)(unsigned long),
> unsigned long data)
> {
> timer->function = function;
> timer->data = data;
> - init_timer(timer);
> + init_timer_key(timer, name, key);
> }
>
> -static inline void setup_timer_on_stack(struct timer_list *timer,
> +static inline void setup_timer_on_stack_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key,
> void (*function)(unsigned long),
> unsigned long data)
> {
> timer->function = function;
> timer->data = data;
> - init_timer_on_stack(timer);
> + init_timer_on_stack_key(timer, name, key);
> }
>
> /**
> --- wireless-testing.orig/kernel/timer.c 2009-01-27 10:12:22.000000000 +0100
> +++ wireless-testing/kernel/timer.c 2009-01-27 19:50:36.000000000 +0100
> @@ -491,14 +491,18 @@ static inline void debug_timer_free(stru
> debug_object_free(timer, &timer_debug_descr);
> }
>
> -static void __init_timer(struct timer_list *timer);
> -
> -void init_timer_on_stack(struct timer_list *timer)
> +static void __init_timer(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key);
> +
> +void init_timer_on_stack_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key)
> {
> debug_object_init_on_stack(timer, &timer_debug_descr);
> - __init_timer(timer);
> + __init_timer(timer, name, key);
> }
> -EXPORT_SYMBOL_GPL(init_timer_on_stack);
> +EXPORT_SYMBOL_GPL(init_timer_on_stack_key);
>
> void destroy_timer_on_stack(struct timer_list *timer)
> {
> @@ -512,7 +516,9 @@ static inline void debug_timer_activate(
> static inline void debug_timer_deactivate(struct timer_list *timer) { }
> #endif
>
> -static void __init_timer(struct timer_list *timer)
> +static void __init_timer(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key)
> {
> timer->entry.next = NULL;
> timer->base = __raw_get_cpu_var(tvec_bases);
> @@ -521,6 +527,7 @@ static void __init_timer(struct timer_li
> timer->start_pid = -1;
> memset(timer->start_comm, 0, TASK_COMM_LEN);
> #endif
> + lockdep_init_map(&timer->lockdep_map, name, key, 0);
> }
>
> /**
> @@ -530,19 +537,23 @@ static void __init_timer(struct timer_li
> * init_timer() must be done to a timer prior calling *any* of the
> * other timer functions.
> */
> -void init_timer(struct timer_list *timer)
> +void init_timer_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key)
> {
> debug_timer_init(timer);
> - __init_timer(timer);
> + __init_timer(timer, name, key);
> }
> -EXPORT_SYMBOL(init_timer);
> +EXPORT_SYMBOL(init_timer_key);
>
> -void init_timer_deferrable(struct timer_list *timer)
> +void init_timer_deferrable_key(struct timer_list *timer,
> + const char *name,
> + struct lock_class_key *key)
> {
> - init_timer(timer);
> + init_timer_key(timer, name, key);
> timer_set_deferrable(timer);
> }
> -EXPORT_SYMBOL(init_timer_deferrable);
> +EXPORT_SYMBOL(init_timer_deferrable_key);
>
> static inline void detach_timer(struct timer_list *timer,
> int clear_pending)
> @@ -789,6 +800,15 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
> */
> int del_timer_sync(struct timer_list *timer)
> {
> +#ifdef CONFIG_LOCKDEP
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + lock_map_acquire(&timer->lockdep_map);
> + lock_map_release(&timer->lockdep_map);
> + local_irq_restore(flags);
> +#endif
> +
> for (;;) {
> int ret = try_to_del_timer_sync(timer);
> if (ret >= 0)
> @@ -861,10 +881,36 @@ static inline void __run_timers(struct t
>
> set_running_timer(base, timer);
> detach_timer(timer, 1);
> +
> spin_unlock_irq(&base->lock);
> {
> int preempt_count = preempt_count();
> +
> +#ifdef CONFIG_LOCKDEP
> + /*
> + * It is permissible to free the timer from
> + * inside the function that is called from
> + * it, this we need to take into account for
> + * lockdep too. To avoid bogus "held lock
> + * freed" warnings as well as problems when
> + * looking into timer->lockdep_map, make a
> + * copy and use that here.
> + */
> + struct lockdep_map lockdep_map =
> + timer->lockdep_map;
> +#endif
> + /*
> + * Couple the lock chain with the lock chain at
> + * del_timer_sync() by acquiring the lock_map
> + * around the fn() call here and in
> + * del_timer_sync().
> + */
> + lock_map_acquire(&lockdep_map);
> +
> fn(data);
> +
> + lock_map_release(&lockdep_map);
> +
> if (preempt_count != preempt_count()) {
> printk(KERN_ERR "huh, entered %p "
> "with preempt_count %08x, exited"
>
>
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