timer: Permit statically-declared work with deferrable timers

Currently, you have to just define a delayed_work uninitialised, and then
initialise it before first use.  That's a tad clumsy.  At risk of playing
mind-games with the compiler, fooling it into doing pointer arithmetic
with compile-time-constants, this lets clients properly initialise delayed
work with deferrable timers statically.

This patch was inspired by the issues which lead Artem Bityutskiy to
commit 8eab945c5616fc984 ("sunrpc: make the cache cleaner workqueue
deferrable").

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
Acked-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 1794674c1a52..cbfb7a355d30 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -48,6 +48,18 @@ extern struct tvec_base boot_tvec_bases;
 #define __TIMER_LOCKDEP_MAP_INITIALIZER(_kn)
 #endif
 
+/*
+ * Note that all tvec_bases are 2 byte aligned and lower bit of
+ * base in timer_list is guaranteed to be zero. Use the LSB to
+ * indicate whether the timer is deferrable.
+ *
+ * A deferrable timer will work normally when the system is busy, but
+ * will not cause a CPU to come out of idle just to service it; instead,
+ * the timer will be serviced when the CPU eventually wakes up with a
+ * subsequent non-deferrable timer.
+ */
+#define TBASE_DEFERRABLE_FLAG           (0x1)
+
 #define TIMER_INITIALIZER(_function, _expires, _data) {         \
                 .entry = { .prev = TIMER_ENTRY_STATIC },        \
                 .function = (_function),                        \
@@ -59,6 +71,19 @@ extern struct tvec_base boot_tvec_bases;
                         __FILE__ ":" __stringify(__LINE__))     \
         }
 
+#define TBASE_MAKE_DEFERRED(ptr) ((struct tvec_base *)          \
+                  ((unsigned char *)(ptr) + TBASE_DEFERRABLE_FLAG))
+
+#define TIMER_DEFERRED_INITIALIZER(_function, _expires, _data) {\
+                .entry = { .prev = TIMER_ENTRY_STATIC },        \
+                .function = (_function),                        \
+                .expires = (_expires),                          \
+                .data = (_data),                                \
+                .base = TBASE_MAKE_DEFERRED(&boot_tvec_bases),  \
+                __TIMER_LOCKDEP_MAP_INITIALIZER(                \
+                        __FILE__ ":" __stringify(__LINE__))     \
+        }
+
 #define DEFINE_TIMER(_name, _function, _expires, _data)         \
         struct timer_list _name =                               \
                 TIMER_INITIALIZER(_function, _expires, _data)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index f11100f96482..88238c15ec3e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -127,12 +127,20 @@ struct execute_work {
         .timer = TIMER_INITIALIZER(NULL, 0, 0),                 \
         }
 
+#define __DEFERRED_WORK_INITIALIZER(n, f) {                     \
+        .work = __WORK_INITIALIZER((n).work, (f)),              \
+        .timer = TIMER_DEFERRED_INITIALIZER(NULL, 0, 0),        \
+        }
+
 #define DECLARE_WORK(n, f)                                      \
         struct work_struct n = __WORK_INITIALIZER(n, f)
 
 #define DECLARE_DELAYED_WORK(n, f)                              \
         struct delayed_work n = __DELAYED_WORK_INITIALIZER(n, f)
 
+#define DECLARE_DEFERRED_WORK(n, f)                             \
+        struct delayed_work n = __DEFERRED_WORK_INITIALIZER(n, f)
+
 /*
  * initialize a work item's function pointer
  */