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Subject[PATCH 3/2] tasklet: implement lockdep deadlock detection
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Date
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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