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

code path 1:
my_function() -> lock(L1); ...; cancel_work_sync(my_work)
[or cancel_rearming_delayed_work(my_work)]

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

you can get a deadlock if my_work.f() is running but my_function()
has acquired L1 already. This patch adds a pseudo-lock to each
struct work_struct 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/lockdep.h | 8 ++++++++
include/linux/workqueue.h | 29 +++++++++++++++++++++++++++++
kernel/workqueue.c | 16 ++++++++++++++++
3 files changed, 53 insertions(+)

--- linux-2.6-git.orig/include/linux/workqueue.h 2007-07-05 13:01:33.978155045 +0200
+++ linux-2.6-git/include/linux/workqueue.h 2007-07-05 13:07:40.969155045 +0200
@@ -8,6 +8,7 @@
#include <linux/timer.h>
#include <linux/linkage.h>
#include <linux/bitops.h>
+#include <linux/lockdep.h>
#include <asm/atomic.h>

struct workqueue_struct;
@@ -28,6 +29,9 @@ struct work_struct {
#define WORK_STRUCT_WQ_DATA_MASK (~WORK_STRUCT_FLAG_MASK)
struct list_head entry;
work_func_t func;
+#ifdef CONFIG_LOCKDEP
+ struct lockdep_map lockdep_map;
+#endif
};

#define WORK_DATA_INIT() ATOMIC_LONG_INIT(0)
@@ -41,10 +45,23 @@ struct execute_work {
struct work_struct work;
};

+#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!
+ */
+#define __WORK_INIT_LOCKDEP_MAP(n, k) \
+ .lockdep_map = STATIC_LOCKDEP_MAP_INIT(n, k),
+#else
+#define __WORK_INIT_LOCKDEP_MAP(n, k)
+#endif
+
#define __WORK_INITIALIZER(n, f) { \
.data = WORK_DATA_INIT(), \
.entry = { &(n).entry, &(n).entry }, \
.func = (f), \
+ __WORK_INIT_LOCKDEP_MAP(#n, &(n)) \
}

#define __DELAYED_WORK_INITIALIZER(n, f) { \
@@ -76,12 +93,24 @@ struct execute_work {
* assignment of the work data initializer allows the compiler
* to generate better code.
*/
+#ifdef CONFIG_LOCKDEP
#define INIT_WORK(_work, _func) \
do { \
+ static struct lock_class_key __key; \
+ \
(_work)->data = (atomic_long_t) WORK_DATA_INIT(); \
+ lockdep_init_map(&(_work)->lockdep_map, #_work, &__key, 0);\
INIT_LIST_HEAD(&(_work)->entry); \
PREPARE_WORK((_work), (_func)); \
} while (0)
+#else
+#define INIT_WORK(_work, _func) \
+ do { \
+ (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \
+ INIT_LIST_HEAD(&(_work)->entry); \
+ PREPARE_WORK((_work), (_func)); \
+ } while (0)
+#endif

#define INIT_DELAYED_WORK(_work, _func) \
do { \
--- linux-2.6-git.orig/kernel/workqueue.c 2007-07-05 13:01:55.728155045 +0200
+++ linux-2.6-git/kernel/workqueue.c 2007-07-05 13:03:40.882155045 +0200
@@ -254,6 +254,17 @@ static void run_workqueue(struct cpu_wor
struct work_struct *work = list_entry(cwq->worklist.next,
struct work_struct, entry);
work_func_t f = work->func;
+#ifdef CONFIG_LOCKDEP
+ /*
+ * It is permissible to free the struct work_struct
+ * 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 work->lockdep_map,
+ * make a copy and use that here.
+ */
+ struct lockdep_map lockdep_map = work->lockdep_map;
+#endif

cwq->current_work = work;
list_del_init(cwq->worklist.next);
@@ -262,7 +273,9 @@ 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_);
+ lock_acquire(&lockdep_map, 0, 0, 0, 2, _THIS_IP_);
f(work);
+ lock_release(&lockdep_map, 1, _THIS_IP_);
lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);

if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
@@ -454,6 +467,9 @@ static void wait_on_work(struct work_str

might_sleep();

+ lock_acquire(&work->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
+ lock_release(&work->lockdep_map, 1, _THIS_IP_);
+
cwq = get_wq_data(work);
if (!cwq)
return;
--- linux-2.6-git.orig/include/linux/lockdep.h 2007-07-05 13:01:34.043155045 +0200
+++ linux-2.6-git/include/linux/lockdep.h 2007-07-05 13:03:40.901155045 +0200
@@ -223,6 +223,14 @@ extern void lockdep_init_map(struct lock
(lock)->dep_map.key, sub)

/*
+ * To initialize a lockdep_map statically use this macro.
+ * Note that _name must not be NULL.
+ */
+#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
+ { .name = (_name), .key = (void *)(_key), }
+
+
+/*
* Acquire a lock.
*
* Values for "read":
--

--

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