irq_work: Use llist in the struct irq_work logic

Use llist in irq_work instead of the lock-less linked list
implementation in irq_work to avoid the code duplication.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1315461646-1379-6-git-send-email-ying.huang@intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 42 insertions, 64 deletions

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 4fa09d4d0b71..6a9e8f5399e2 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -1,20 +1,23 @@
 #ifndef _LINUX_IRQ_WORK_H
 #define _LINUX_IRQ_WORK_H
 
+#include <linux/llist.h>
+
 struct irq_work {
-        struct irq_work *next;
+        unsigned long flags;
+        struct llist_node llnode;
         void (*func)(struct irq_work *);
 };
 
 static inline
-void init_irq_work(struct irq_work *entry, void (*func)(struct irq_work *))
+void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
 {
-        entry->next = NULL;
-        entry->func = func;
+        work->flags = 0;
+        work->func = func;
 }
 
-bool irq_work_queue(struct irq_work *entry);
+bool irq_work_queue(struct irq_work *work);
 void irq_work_run(void);
-void irq_work_sync(struct irq_work *entry);
+void irq_work_sync(struct irq_work *work);
 
 #endif /* _LINUX_IRQ_WORK_H */
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index c58fa7da8aef..6f0a4310defd 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -17,54 +17,34 @@
  * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
  * pending   next, 3 -> {busy}          : queued, pending callback
  * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
- *
- * We use the lower two bits of the next pointer to keep PENDING and BUSY
- * flags.
  */
 
 #define IRQ_WORK_PENDING        1UL
 #define IRQ_WORK_BUSY           2UL
 #define IRQ_WORK_FLAGS          3UL
 
-static inline bool irq_work_is_set(struct irq_work *entry, int flags)
-{
-        return (unsigned long)entry->next & flags;
-}
-
-static inline struct irq_work *irq_work_next(struct irq_work *entry)
-{
-        unsigned long next = (unsigned long)entry->next;
-        next &= ~IRQ_WORK_FLAGS;
-        return (struct irq_work *)next;
-}
-
-static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
-{
-        unsigned long next = (unsigned long)entry;
-        next |= flags;
-        return (struct irq_work *)next;
-}
-
-static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
+static DEFINE_PER_CPU(struct llist_head, irq_work_list);
 
 /*
  * Claim the entry so that no one else will poke at it.
  */
-static bool irq_work_claim(struct irq_work *entry)
+static bool irq_work_claim(struct irq_work *work)
 {
-        struct irq_work *next, *nflags;
+        unsigned long flags, nflags;
 
-        do {
-                next = entry->next;
-                if ((unsigned long)next & IRQ_WORK_PENDING)
+        for (;;) {
+                flags = work->flags;
+                if (flags & IRQ_WORK_PENDING)
                         return false;
-                nflags = next_flags(next, IRQ_WORK_FLAGS);
-        } while (cmpxchg(&entry->next, next, nflags) != next);
+                nflags = flags | IRQ_WORK_FLAGS;
+                if (cmpxchg(&work->flags, flags, nflags) == flags)
+                        break;
+                cpu_relax();
+        }
 
         return true;
 }
 
-
 void __weak arch_irq_work_raise(void)
 {
         /*
@@ -75,20 +55,15 @@ void __weak arch_irq_work_raise(void)
 /*
  * Queue the entry and raise the IPI if needed.
  */
-static void __irq_work_queue(struct irq_work *entry)
+static void __irq_work_queue(struct irq_work *work)
 {
-        struct irq_work *next;
+        bool empty;
 
         preempt_disable();
 
-        do {
-                next = __this_cpu_read(irq_work_list);
-                /* Can assign non-atomic because we keep the flags set. */
-                entry->next = next_flags(next, IRQ_WORK_FLAGS);
-        } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
-
+        empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
         /* The list was empty, raise self-interrupt to start processing. */
-        if (!irq_work_next(entry))
+        if (empty)
                 arch_irq_work_raise();
 
         preempt_enable();
@@ -100,16 +75,16 @@ static void __irq_work_queue(struct irq_work *entry)
  *
  * Can be re-enqueued while the callback is still in progress.
  */
-bool irq_work_queue(struct irq_work *entry)
+bool irq_work_queue(struct irq_work *work)
 {
-        if (!irq_work_claim(entry)) {
+        if (!irq_work_claim(work)) {
                 /*
                  * Already enqueued, can't do!
                  */
                 return false;
         }
 
-        __irq_work_queue(entry);
+        __irq_work_queue(work);
         return true;
 }
 EXPORT_SYMBOL_GPL(irq_work_queue);
@@ -120,34 +95,34 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
  */
 void irq_work_run(void)
 {
-        struct irq_work *list;
+        struct irq_work *work;
+        struct llist_head *this_list;
+        struct llist_node *llnode;
 
-        if (this_cpu_read(irq_work_list) == NULL)
+        this_list = &__get_cpu_var(irq_work_list);
+        if (llist_empty(this_list))
                 return;
 
         BUG_ON(!in_irq());
         BUG_ON(!irqs_disabled());
 
-        list = this_cpu_xchg(irq_work_list, NULL);
-
-        while (list != NULL) {
-                struct irq_work *entry = list;
+        llnode = llist_del_all(this_list);
+        while (llnode != NULL) {
+                work = llist_entry(llnode, struct irq_work, llnode);
 
-                list = irq_work_next(list);
+                llnode = llnode->next;
 
                 /*
-                 * Clear the PENDING bit, after this point the @entry
+                 * Clear the PENDING bit, after this point the @work
                  * can be re-used.
                  */
-                entry->next = next_flags(NULL, IRQ_WORK_BUSY);
-                entry->func(entry);
+                work->flags = IRQ_WORK_BUSY;
+                work->func(work);
                 /*
                  * Clear the BUSY bit and return to the free state if
                  * no-one else claimed it meanwhile.
                  */
-                (void)cmpxchg(&entry->next,
-                              next_flags(NULL, IRQ_WORK_BUSY),
-                              NULL);
+                (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0);
         }
 }
 EXPORT_SYMBOL_GPL(irq_work_run);
@@ -156,11 +131,11 @@ EXPORT_SYMBOL_GPL(irq_work_run);
  * Synchronize against the irq_work @entry, ensures the entry is not
  * currently in use.
  */
-void irq_work_sync(struct irq_work *entry)
+void irq_work_sync(struct irq_work *work)
 {
         WARN_ON_ONCE(irqs_disabled());
 
-        while (irq_work_is_set(entry, IRQ_WORK_BUSY))
+        while (work->flags & IRQ_WORK_BUSY)
                 cpu_relax();
 }
 EXPORT_SYMBOL_GPL(irq_work_sync);