8 files changed, 23 insertions, 73 deletions

diff --git a/include/asm-arm/system.h b/include/asm-arm/system.h
index 39dd7008013c..3d0d2860b6db 100644
--- a/include/asm-arm/system.h
+++ b/include/asm-arm/system.h
@@ -145,34 +145,12 @@ extern unsigned int user_debug;
 #define set_wmb(var, value) do { var = value; wmb(); } while (0)
 #define nop() __asm__ __volatile__("mov\tr0,r0\t@ nop\n\t");
 
-#ifdef CONFIG_SMP
 /*
- * Define our own context switch locking.  This allows us to enable
- * interrupts over the context switch, otherwise we end up with high
- * interrupt latency.  The real problem area is switch_mm() which may
- * do a full cache flush.
+ * switch_mm() may do a full cache flush over the context switch,
+ * so enable interrupts over the context switch to avoid high
+ * latency.
  */
-#define prepare_arch_switch(rq,next)                                    \
-do {                                                                    \
-        spin_lock(&(next)->switch_lock);                                \
-        spin_unlock_irq(&(rq)->lock);                                   \
-} while (0)
-
-#define finish_arch_switch(rq,prev)                                     \
-        spin_unlock(&(prev)->switch_lock)
-
-#define task_running(rq,p)                                              \
-        ((rq)->curr == (p) || spin_is_locked(&(p)->switch_lock))
-#else
-/*
- * Our UP-case is more simple, but we assume knowledge of how
- * spin_unlock_irq() and friends are implemented.  This avoids
- * us needlessly decrementing and incrementing the preempt count.
- */
-#define prepare_arch_switch(rq,next)    local_irq_enable()
-#define finish_arch_switch(rq,prev)     spin_unlock(&(rq)->lock)
-#define task_running(rq,p)              ((rq)->curr == (p))
-#endif
+#define __ARCH_WANT_INTERRUPTS_ON_CTXSW
 
 /*
  * switch_to(prev, next) should switch from task `prev' to `next'
diff --git a/include/asm-ia64/system.h b/include/asm-ia64/system.h
index 6f516e76d1f0..cd2cf76b2db1 100644
--- a/include/asm-ia64/system.h
+++ b/include/asm-ia64/system.h
@@ -183,8 +183,6 @@ do {								\
 
 #ifdef __KERNEL__
 
-#define prepare_to_switch()    do { } while(0)
-
 #ifdef CONFIG_IA32_SUPPORT
 # define IS_IA32_PROCESS(regs)  (ia64_psr(regs)->is != 0)
 #else
@@ -274,13 +272,7 @@ extern void ia64_load_extra (struct task_struct *task);
  * of that CPU which will not be released, because there we wait for the
  * tasklist_lock to become available.
  */
-#define prepare_arch_switch(rq, next)           \
-do {                                            \
-        spin_lock(&(next)->switch_lock);        \
-        spin_unlock(&(rq)->lock);               \
-} while (0)
-#define finish_arch_switch(rq, prev)    spin_unlock_irq(&(prev)->switch_lock)
-#define task_running(rq, p)             ((rq)->curr == (p) || spin_is_locked(&(p)->switch_lock))
+#define __ARCH_WANT_UNLOCKED_CTXSW
 
 #define ia64_platform_is(x) (strcmp(x, platform_name) == 0)
 
diff --git a/include/asm-mips/system.h b/include/asm-mips/system.h
index 888fd8908467..169f3d4265b1 100644
--- a/include/asm-mips/system.h
+++ b/include/asm-mips/system.h
@@ -422,16 +422,10 @@ extern void __die_if_kernel(const char *, struct pt_regs *, const char *file,
 extern int stop_a_enabled;
 
 /*
- * Taken from include/asm-ia64/system.h; prevents deadlock on SMP
+ * See include/asm-ia64/system.h; prevents deadlock on SMP
  * systems.
  */
-#define prepare_arch_switch(rq, next)           \
-do {                                            \
-        spin_lock(&(next)->switch_lock);        \
-        spin_unlock(&(rq)->lock);               \
-} while (0)
-#define finish_arch_switch(rq, prev)    spin_unlock_irq(&(prev)->switch_lock)
-#define task_running(rq, p)             ((rq)->curr == (p) || spin_is_locked(&(p)->switch_lock))
+#define __ARCH_WANT_UNLOCKED_CTXSW
 
 #define arch_align_stack(x) (x)
 
diff --git a/include/asm-s390/system.h b/include/asm-s390/system.h
index e3cb3ce1d24a..b4a9f05a93d6 100644
--- a/include/asm-s390/system.h
+++ b/include/asm-s390/system.h
@@ -104,29 +104,18 @@ static inline void restore_access_regs(unsigned int *acrs)
         prev = __switch_to(prev,next);                                       \
 } while (0)
 
-#define prepare_arch_switch(rq, next)   do { } while(0)
-#define task_running(rq, p)             ((rq)->curr == (p))
-
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
 extern void account_user_vtime(struct task_struct *);
 extern void account_system_vtime(struct task_struct *);
-
-#define finish_arch_switch(rq, prev) do {                                    \
-        set_fs(current->thread.mm_segment);                                  \
-        spin_unlock(&(rq)->lock);                                            \
-        account_system_vtime(prev);                                          \
-        local_irq_enable();                                                  \
-} while (0)
-
 #else
+#define account_system_vtime(prev) do { } while (0)
+#endif
 
 #define finish_arch_switch(rq, prev) do {                                    \
         set_fs(current->thread.mm_segment);                                  \
-        spin_unlock_irq(&(rq)->lock);                                        \
+        account_system_vtime(prev);                                          \
 } while (0)
 
-#endif
-
 #define nop() __asm__ __volatile__ ("nop")
 
 #define xchg(ptr,x) \
diff --git a/include/asm-sparc/system.h b/include/asm-sparc/system.h
index 80cf20cfaee1..898562ebe94c 100644
--- a/include/asm-sparc/system.h
+++ b/include/asm-sparc/system.h
@@ -101,7 +101,7 @@ extern void fpsave(unsigned long *fpregs, unsigned long *fsr,
  * SWITCH_ENTER and SWITH_DO_LAZY_FPU do not work yet (e.g. SMP does not work)
  * XXX WTF is the above comment? Found in late teen 2.4.x.
  */
-#define prepare_arch_switch(rq, next) do { \
+#define prepare_arch_switch(next) do { \
         __asm__ __volatile__( \
         ".globl\tflush_patch_switch\nflush_patch_switch:\n\t" \
         "save %sp, -0x40, %sp; save %sp, -0x40, %sp; save %sp, -0x40, %sp\n\t" \
@@ -109,8 +109,6 @@ extern void fpsave(unsigned long *fpregs, unsigned long *fsr,
         "save %sp, -0x40, %sp\n\t" \
         "restore; restore; restore; restore; restore; restore; restore"); \
 } while(0)
-#define finish_arch_switch(rq, next)    spin_unlock_irq(&(rq)->lock)
-#define task_running(rq, p)             ((rq)->curr == (p))
 
         /* Much care has gone into this code, do not touch it.
          *
diff --git a/include/asm-sparc64/system.h b/include/asm-sparc64/system.h
index fd12ca386f48..f9be2c5b4dc9 100644
--- a/include/asm-sparc64/system.h
+++ b/include/asm-sparc64/system.h
@@ -139,19 +139,13 @@ extern void __flushw_user(void);
 #define flush_user_windows flushw_user
 #define flush_register_windows flushw_all
 
-#define prepare_arch_switch(rq, next)           \
-do {    spin_lock(&(next)->switch_lock);        \
-        spin_unlock(&(rq)->lock);               \
+/* Don't hold the runqueue lock over context switch */
+#define __ARCH_WANT_UNLOCKED_CTXSW
+#define prepare_arch_switch(next)               \
+do {                                            \
         flushw_all();                           \
 } while (0)
 
-#define finish_arch_switch(rq, prev)            \
-do {    spin_unlock_irq(&(prev)->switch_lock);  \
-} while (0)
-
-#define task_running(rq, p) \
-        ((rq)->curr == (p) || spin_is_locked(&(p)->switch_lock))
-
         /* See what happens when you design the chip correctly?
          *
          * We tell gcc we clobber all non-fixed-usage registers except
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index a6a8c1a38d5e..03206a425d7a 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -108,7 +108,6 @@ extern struct group_info init_groups;
         .blocked        = {{0}},                                        \
         .alloc_lock     = SPIN_LOCK_UNLOCKED,                           \
         .proc_lock      = SPIN_LOCK_UNLOCKED,                           \
-        .switch_lock    = SPIN_LOCK_UNLOCKED,                           \
         .journal_info   = NULL,                                         \
         .cpu_timers     = INIT_CPU_TIMERS(tsk.cpu_timers),              \
 }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 36a10781c3f3..d27be9337425 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -368,6 +368,11 @@ struct signal_struct {
 #endif
 };
 
+/* Context switch must be unlocked if interrupts are to be enabled */
+#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
+# define __ARCH_WANT_UNLOCKED_CTXSW
+#endif
+
 /*
  * Bits in flags field of signal_struct.
  */
@@ -594,6 +599,9 @@ struct task_struct {
 
         int lock_depth;         /* BKL lock depth */
 
+#if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
+        int oncpu;
+#endif
         int prio, static_prio;
         struct list_head run_list;
         prio_array_t *array;
@@ -716,8 +724,6 @@ struct task_struct {
         spinlock_t alloc_lock;
 /* Protection of proc_dentry: nesting proc_lock, dcache_lock, write_lock_irq(&tasklist_lock); */
         spinlock_t proc_lock;
-/* context-switch lock */
-        spinlock_t switch_lock;
 
 /* journalling filesystem info */
         void *journal_info;