Re: contention on profile_lock

[Jesse Barnes <jbarnes@engr.sgi.com>]

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On Thursday, November 4, 2004 12:49 pm, Jesse Barnes wrote:
> John pointed out that this breaks modules.  Would registering and
> unregistering a function pointer thus be module safe?  Dipankar, hopefully
> you have something better?
>
> static int timer_start(void)
> {
>  /* Setup the callback pointer */
>  oprofile_timer_notify = oprofile_timer;
>  return 0;
> }
>
>
> static void timer_stop(void)
> {
>  /* Tear down the callback pointer after sync_kernel */
>  synchronize_kernel();
>  oprofile_timer_notify = NULL;
> }

Ok, here's another one that uses this approach.  Hopefully it satisfies all 
parties?  (Compile tested only so far.)

Thanks,
Jesse

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===== drivers/oprofile/timer_int.c 1.8 vs edited =====
--- 1.8/drivers/oprofile/timer_int.c	2004-09-03 16:55:27 -07:00
+++ edited/drivers/oprofile/timer_int.c	2004-11-04 13:54:13 -08:00
@@ -13,33 +13,31 @@
 #include <linux/oprofile.h>
 #include <linux/profile.h>
 #include <linux/init.h>
+#include <linux/rcupdate.h>
 #include <asm/ptrace.h>
  
-static int timer_notify(struct notifier_block * self, unsigned long val, void * data)
+static int timer_notify(struct pt_regs *regs)
 {
-	struct pt_regs * regs = (struct pt_regs *)data;
 	int cpu = smp_processor_id();
 	unsigned long eip = profile_pc(regs);
  
 	oprofile_add_sample(eip, !user_mode(regs), 0, cpu);
 	return 0;
 }
- 
- 
-static struct notifier_block timer_notifier = {
-	.notifier_call	= timer_notify,
-};
- 
 
 static int timer_start(void)
 {
-	return register_profile_notifier(&timer_notifier);
+	/* Setup the callback pointer */
+	oprofile_timer_notify = timer_notify;
+	return 0;
 }
 
 
 static void timer_stop(void)
 {
-	unregister_profile_notifier(&timer_notifier);
+	/* Tear down the callback pointer after sync_kernel */
+	synchronize_kernel();
+	oprofile_timer_notify = NULL;
 }
 
 
===== include/linux/oprofile.h 1.10 vs edited =====
--- 1.10/include/linux/oprofile.h	2004-06-24 01:56:02 -07:00
+++ edited/include/linux/oprofile.h	2004-11-04 13:54:04 -08:00
@@ -105,5 +105,8 @@
 
 /** lock for read/write safety */
 extern spinlock_t oprofilefs_lock;
+
+/* Timer based profiling hook */
+extern int (*oprofile_timer_notify)(struct pt_regs *);
  
 #endif /* OPROFILE_H */
===== kernel/profile.c 1.14 vs edited =====
--- 1.14/kernel/profile.c	2004-10-19 02:40:31 -07:00
+++ edited/kernel/profile.c	2004-11-04 13:50:36 -08:00
@@ -22,6 +22,7 @@
 #include <linux/cpumask.h>
 #include <linux/cpu.h>
 #include <linux/profile.h>
+#include <linux/oprofile.h>
 #include <linux/highmem.h>
 #include <asm/sections.h>
 #include <asm/semaphore.h>
@@ -34,6 +35,9 @@
 #define NR_PROFILE_HIT		(PAGE_SIZE/sizeof(struct profile_hit))
 #define NR_PROFILE_GRP		(NR_PROFILE_HIT/PROFILE_GRPSZ)
 
+/* Oprofile timer tick hook */
+int (*oprofile_timer_notify)(struct pt_regs *);
+
 static atomic_t *prof_buffer;
 static unsigned long prof_len, prof_shift;
 static int prof_on;
@@ -168,38 +172,6 @@
 	return err;
 }
 
-static struct notifier_block * profile_listeners;
-static rwlock_t profile_lock = RW_LOCK_UNLOCKED;
- 
-int register_profile_notifier(struct notifier_block * nb)
-{
-	int err;
-	write_lock_irq(&profile_lock);
-	err = notifier_chain_register(&profile_listeners, nb);
-	write_unlock_irq(&profile_lock);
-	return err;
-}
-
-
-int unregister_profile_notifier(struct notifier_block * nb)
-{
-	int err;
-	write_lock_irq(&profile_lock);
-	err = notifier_chain_unregister(&profile_listeners, nb);
-	write_unlock_irq(&profile_lock);
-	return err;
-}
-
-
-void profile_hook(struct pt_regs * regs)
-{
-	read_lock(&profile_lock);
-	notifier_call_chain(&profile_listeners, 0, regs);
-	read_unlock(&profile_lock);
-}
-
-EXPORT_SYMBOL_GPL(register_profile_notifier);
-EXPORT_SYMBOL_GPL(unregister_profile_notifier);
 EXPORT_SYMBOL_GPL(task_handoff_register);
 EXPORT_SYMBOL_GPL(task_handoff_unregister);
 
@@ -394,8 +366,8 @@
 
 void profile_tick(int type, struct pt_regs *regs)
 {
-	if (type == CPU_PROFILING)
-		profile_hook(regs);
+	if (type == CPU_PROFILING && oprofile_timer_notify)
+		oprofile_timer_notify(regs);
 	if (!user_mode(regs) && cpu_isset(smp_processor_id(), prof_cpu_mask))
 		profile_hit(type, (void *)profile_pc(regs));
 }