uml: fix timer switching

Fix up the switching between virtual and real timers.  The idle loop sleeps,
so the timer at that point must be real time.  At all other times, the timer
must be virtual.  Even when userspace is running, and the kernel is asleep,
the virtual timer is correct because the process timer will be running and the
process timer will be firing.

The timer switch used to be in the context switch and timer handler code.
This is moved to the idle loop and the signal handler, making it much more
clear why it is happening.

switch_timers now returns the old timer type so that it may be restored.  The
signal handler uses this in order to restore the previous timer type when it
returns.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 26 insertions, 21 deletions

diff --git a/arch/um/include/os.h b/arch/um/include/os.h
index e861c8a..12de1ea 100644
--- a/arch/um/include/os.h
+++ b/arch/um/include/os.h
@@ -250,7 +250,7 @@ extern void os_dump_core(void);
 /* time.c */
 #define BILLION (1000 * 1000 * 1000)
 
-extern void switch_timers(int to_real);
+extern int switch_timers(int to_real);
 extern void idle_sleep(int secs);
 extern int set_interval(int is_virtual);
 extern void disable_timer(void);
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 8a6882d..56d75af 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -95,18 +95,11 @@ void *_switch_to(void *prev, void *next, void *last)
 	do {
 		current->thread.saved_task = NULL;
 
-		/* XXX need to check runqueues[cpu].idle */
-		if (current->pid == 0)
-			switch_timers(0);
-
 		switch_threads(&from->thread.switch_buf,
 			       &to->thread.switch_buf);
 
 		arch_switch_to(current->thread.prev_sched, current);
 
-		if (current->pid == 0)
-			switch_timers(1);
-
 		if (current->thread.saved_task)
 			show_regs(&(current->thread.regs));
 		next= current->thread.saved_task;
@@ -251,7 +244,9 @@ void default_idle(void)
 		if (need_resched())
 			schedule();
 
+		switch_timers(1);
 		idle_sleep(10);
+		switch_timers(0);
 	}
 }
 
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 49c113b..1c5267e 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -59,17 +59,11 @@ static void real_alarm_handler(int sig, struct sigcontext *sc)
 {
 	struct uml_pt_regs regs;
 
-	if (sig == SIGALRM)
-		switch_timers(0);
-
 	if (sc != NULL)
 		copy_sc(&regs, sc);
 	regs.is_user = 0;
 	unblock_signals();
 	timer_handler(sig, &regs);
-
-	if (sig == SIGALRM)
-		switch_timers(1);
 }
 
 void alarm_handler(int sig, struct sigcontext *sc)
@@ -116,6 +110,7 @@ void (*handlers[_NSIG])(int sig, struct sigcontext *sc);
 void handle_signal(int sig, struct sigcontext *sc)
 {
 	unsigned long pending = 1UL << sig;
+	int timer = switch_timers(0);
 
 	do {
 		int nested, bail;
@@ -152,6 +147,8 @@ void handle_signal(int sig, struct sigcontext *sc)
 		if (!nested)
 			pending = from_irq_stack(nested);
 	} while (pending);
+
+	switch_timers(timer);
 }
 
 extern void hard_handler(int sig);
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
index 5939653..a16a0f4 100644
--- a/arch/um/os-Linux/time.c
+++ b/arch/um/os-Linux/time.c
@@ -12,6 +12,8 @@
 #include "os.h"
 #include "user.h"
 
+static int is_real_timer = 0;
+
 int set_interval(int is_virtual)
 {
 	int usec = 1000000/UM_HZ;
@@ -39,12 +41,14 @@ void disable_timer(void)
 	signal(SIGVTALRM, SIG_IGN);
 }
 
-void switch_timers(int to_real)
+int switch_timers(int to_real)
 {
 	struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
-	struct itimerval enable = ((struct itimerval) { { 0, 1000000/UM_HZ },
-							{ 0, 1000000/UM_HZ }});
-	int old, new;
+	struct itimerval enable;
+	int old, new, old_type = is_real_timer;
+
+	if(to_real == old_type)
+		return to_real;
 
 	if (to_real) {
 		old = ITIMER_VIRTUAL;
@@ -55,10 +59,19 @@ void switch_timers(int to_real)
 		new = ITIMER_VIRTUAL;
 	}
 
-	if ((setitimer(old, &disable, NULL) < 0) ||
-	    (setitimer(new, &enable, NULL)))
-		printk(UM_KERN_ERR "switch_timers - setitimer failed, "
+	if (setitimer(old, &disable, &enable) < 0)
+		printk(UM_KERN_ERR "switch_timers - setitimer disable failed, "
+		       "errno = %d\n", errno);
+
+	if((enable.it_value.tv_sec == 0) && (enable.it_value.tv_usec == 0))
+		enable.it_value = enable.it_interval;
+
+	if (setitimer(new, &enable, NULL))
+		printk(UM_KERN_ERR "switch_timers - setitimer enable failed, "
 		       "errno = %d\n", errno);
+
+	is_real_timer = to_real;
+	return old_type;
 }
 
 unsigned long long os_nsecs(void)