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Subject[PATCH (resend) 1/2] workqueue: debug flushing deadlocks with lockdep
In the following scenario:

code path 1:
my_function() -> lock(L1); ...; flush_workqueue(); ...

code path 2:
run_workqueue() -> my_work() -> ...; lock(L1); ...

you can get a deadlock when my_work() is queued or running
but my_function() has acquired L1 already.

This patch adds a pseudo-lock to each workqueue to make lockdep
warn about this scenario.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

---
include/linux/workqueue.h | 20 +++++++++++++++++---
kernel/workqueue.c | 20 +++++++++++++++++---
2 files changed, 34 insertions(+), 6 deletions(-)
--- wireless-dev.orig/kernel/workqueue.c 2007-07-17 13:45:31.170964463 +0200
+++ wireless-dev/kernel/workqueue.c 2007-07-17 14:52:07.980964463 +0200
@@ -32,6 +32,7 @@
#include <linux/freezer.h>
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
+#include <linux/lockdep.h>

/*
* The per-CPU workqueue (if single thread, we always use the first
@@ -61,6 +62,9 @@ struct workqueue_struct {
const char *name;
int singlethread;
int freezeable; /* Freeze threads during suspend */
+#ifdef CONFIG_LOCKDEP
+ struct lockdep_map lockdep_map;
+#endif
};

/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
@@ -257,7 +261,9 @@ static void run_workqueue(struct cpu_wor

BUG_ON(get_wq_data(work) != cwq);
work_clear_pending(work);
+ lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
f(work);
+ lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);

if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
@@ -376,6 +382,8 @@ void fastcall flush_workqueue(struct wor
int cpu;

might_sleep();
+ lock_acquire(&wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
+ lock_release(&wq->lockdep_map, 1, _THIS_IP_);
for_each_cpu_mask(cpu, *cpu_map)
flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
}
@@ -695,8 +703,10 @@ static void start_workqueue_thread(struc
}
}

-struct workqueue_struct *__create_workqueue(const char *name,
- int singlethread, int freezeable)
+struct workqueue_struct *__create_workqueue_key(const char *name,
+ int singlethread,
+ int freezeable,
+ struct lock_class_key *key)
{
struct workqueue_struct *wq;
struct cpu_workqueue_struct *cwq;
@@ -713,6 +723,7 @@ struct workqueue_struct *__create_workqu
}

wq->name = name;
+ lockdep_init_map(&wq->lockdep_map, name, key, 0);
wq->singlethread = singlethread;
wq->freezeable = freezeable;
INIT_LIST_HEAD(&wq->list);
@@ -741,7 +752,7 @@ struct workqueue_struct *__create_workqu
}
return wq;
}
-EXPORT_SYMBOL_GPL(__create_workqueue);
+EXPORT_SYMBOL_GPL(__create_workqueue_key);

static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
{
@@ -752,6 +763,9 @@ static void cleanup_workqueue_thread(str
if (cwq->thread == NULL)
return;

+ lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
+ lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);
+
/*
* If the caller is CPU_DEAD the single flush_cpu_workqueue()
* is not enough, a concurrent flush_workqueue() can insert a
--- wireless-dev.orig/include/linux/workqueue.h 2007-07-17 13:45:29.920964463 +0200
+++ wireless-dev/include/linux/workqueue.h 2007-07-17 14:52:07.890964463 +0200
@@ -118,9 +118,23 @@ struct execute_work {
clear_bit(WORK_STRUCT_PENDING, work_data_bits(work))


-extern struct workqueue_struct *__create_workqueue(const char *name,
- int singlethread,
- int freezeable);
+extern struct workqueue_struct *
+__create_workqueue_key(const char *name, int singlethread,
+ int freezeable, struct lock_class_key *key);
+
+#ifdef CONFIG_LOCKDEP
+#define __create_workqueue(name, singlethread, freezeable) \
+({ \
+ static struct lock_class_key __key; \
+ \
+ __create_workqueue_key((name), (singlethread), \
+ (freezeable), &__key); \
+})
+#else
+#define __create_workqueue(name, singlethread, freezeable) \
+ __create_workqueue_key((name), (singlethread), (freezeable), NULL)
+#endif
+
#define create_workqueue(name) __create_workqueue((name), 0, 0)
#define create_freezeable_workqueue(name) __create_workqueue((name), 1, 1)
#define create_singlethread_workqueue(name) __create_workqueue((name), 1, 0)
--

-
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