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.

[akpm@linux-foundation.org: coding-style fixes]
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 54 insertions, 3 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index f6279f68a827..4c4d236ded18 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -276,6 +276,14 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
                                  (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":
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ce6badc98f6d..7daafdc2514b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -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 {                                                    \
@@ -118,9 +147,23 @@ 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)