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    Subject[PATCH 3/2] tasklet: implement lockdep deadlock detection
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    The tasklet code can deadlock when you try to disable a tasklet
    under a lock that the tasklet requires. This patch implements
    lockdep checking for this situation.

    Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
    ---
    I don't have an actual instance of this in the kernel either, but my
    test case triggers correctly.

    This was easy, but I think it's probably unlikely that somebody will do
    this mistake.

    include/linux/interrupt.h | 41 ++++++++++++++++++++++++++++++++++++-----
    kernel/softirq.c | 10 +++++++---
    2 files changed, 43 insertions(+), 8 deletions(-)

    --- wireless-testing.orig/include/linux/interrupt.h 2008-10-23 21:42:58.495547519 +0200
    +++ wireless-testing/include/linux/interrupt.h 2008-10-23 22:09:18.911743812 +0200
    @@ -299,13 +299,31 @@ struct tasklet_struct
    atomic_t count;
    void (*func)(unsigned long);
    unsigned long data;
    +#ifdef CONFIG_LOCKDEP
    + struct lockdep_map lock_map;
    +#endif
    };

    -#define DECLARE_TASKLET(name, func, data) \
    -struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(0), func, data }
    +#ifdef CONFIG_LOCKDEP
    +#define __TASKLET_LOCK_INIT(n, k) .lock_map = STATIC_LOCKDEP_MAP_INIT(n, k),
    +#else
    +#define __TASKLET_LOCK_INIT(n, k)
    +#endif

    +#define __DECLARE_TASKLET(name, _func, _data, c)\
    +struct tasklet_struct name = { \
    + .next = NULL, \
    + .state = 0, \
    + .count = ATOMIC_INIT(c), \
    + .func = _func, \
    + .data = _data, \
    + __TASKLET_LOCK_INIT(#name, &name) \
    +}
    +
    +#define DECLARE_TASKLET(name, func, data) \
    + __DECLARE_TASKLET(name, func, data, 0)
    #define DECLARE_TASKLET_DISABLED(name, func, data) \
    -struct tasklet_struct name = { NULL, 0, ATOMIC_INIT(1), func, data }
    + __DECLARE_TASKLET(name, func, data, 1)


    enum
    @@ -328,6 +346,8 @@ static inline void tasklet_unlock(struct

    static inline void tasklet_unlock_wait(struct tasklet_struct *t)
    {
    + lock_map_acquire_noirq(&t->lock_map);
    + lock_map_release(&t->lock_map);
    while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
    }
    #else
    @@ -380,8 +400,19 @@ static inline void tasklet_hi_enable(str

    extern void tasklet_kill(struct tasklet_struct *t);
    extern void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu);
    -extern void tasklet_init(struct tasklet_struct *t,
    - void (*func)(unsigned long), unsigned long data);
    +extern void tasklet_init_key(struct tasklet_struct *t,
    + const char *name, struct lock_class_key *key,
    + void (*func)(unsigned long), unsigned long data);
    +
    +#ifdef CONFIG_LOCKDEP
    +#define tasklet_init(t, f, d) \
    + do { \
    + static struct lock_class_key __key; \
    + tasklet_init_key((t), #t, &__key, (f), (d)); \
    + } while (0)
    +#else
    +#define tasklet_init(t, f, d) tasklet_init_key((t), NULL, NULL, (f), (d))
    +#endif

    /*
    * Autoprobing for irqs:
    --- wireless-testing.orig/kernel/softirq.c 2008-10-23 21:46:26.808921693 +0200
    +++ wireless-testing/kernel/softirq.c 2008-10-23 22:01:34.382734952 +0200
    @@ -383,7 +383,9 @@ static void tasklet_action(struct softir
    if (!atomic_read(&t->count)) {
    if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
    BUG();
    + lock_map_acquire_noirq(&t->lock_map);
    t->func(t->data);
    + lock_map_release(&t->lock_map);
    tasklet_unlock(t);
    continue;
    }
    @@ -435,17 +437,19 @@ static void tasklet_hi_action(struct sof
    }


    -void tasklet_init(struct tasklet_struct *t,
    - void (*func)(unsigned long), unsigned long data)
    +void tasklet_init_key(struct tasklet_struct *t,
    + const char *name, struct lock_class_key *key,
    + void (*func)(unsigned long), unsigned long data)
    {
    t->next = NULL;
    t->state = 0;
    atomic_set(&t->count, 0);
    t->func = func;
    t->data = data;
    + lockdep_init_map(&t->lock_map, name, key, 0);
    }

    -EXPORT_SYMBOL(tasklet_init);
    +EXPORT_SYMBOL(tasklet_init_key);

    void tasklet_kill(struct tasklet_struct *t)
    {



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