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2.4: introduce get_cpu() and put_cpu()

PATCH In review Robert Love 2 participants 3 messages Oct 6, 2002

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Robert Love

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#0 lore raw

PATCH 1/1 2.4: introduce get_cpu() and put_cpu()

Master Marcelo,

In 2.5, it is unsafe to assume the current processor does not change out from under you - thus you must be atomic when calling smp_processor_id(). We introduced the get_cpu() and put_cpu() methods to provide a safe way to access the current processor.

This patch back-ports those interfaces to 2.4. Note they do nothing
special: get_cpu() simply returns smp_processor_id() and put_cpu() is a no-op. But this will allow easier back-porting from 2.5 and common code-base for drivers, etc. It also does not hurt to be explicit that you do not want the processor to change.

As an example, I converted one use of smp_processor_id() to the new interface.

Patch is against 2.4.20-pre9, please apply.

Robert Love

arch/i386/kernel/ioport.c +4 -1
diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c
@@ -55,12 +55,15 @@
 asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
 {
 	struct thread_struct * t = &current->thread;
-	struct tss_struct * tss = init_tss + smp_processor_id();
+	struct tss_struct * tss;
 
 	if ((from + num <= from) || (from + num > IO_BITMAP_SIZE*32))
 		return -EINVAL;
 	if (turn_on && !capable(CAP_SYS_RAWIO))
 		return -EPERM;
+
+	tss = init_tss + get_cpu();
+
 	/*
 	 * If it's the first ioperm() call in this thread's lifetime, set the
 	 * IO bitmap up. ioperm() is much less timing critical than clone(),
include/linux/smp.h +6 -2
diff -urN linux-2.4.20-pre9/include/linux/smp.h linux/include/linux/smp.h
@@ -87,5 +87,9 @@
 #define smp_call_function(func,info,retry,wait)	({ 0; })
 #define cpu_online_map				1
 
-#endif
-#endif
+#endif /* !CONFIG_SMP */
+
+#define get_cpu()	smp_processor_id()
+#define put_cpu()	do { } while(0)
+
+#endif /* __LINUX_SMP_H */
#1 lore raw
Quoted 11 lines · Robert Love

diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c

arch/i386/kernel/ioport.c 2002-10-06 15:21:04.000000000 -0400 renamed from arch/i386/kernel/ioport.c 2002-10-06 14:58:01.000000000 -0400 +1 -1
@@ -55,12 +55,15 @@
 asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
 {
        struct thread_struct * t = &current->thread;
-       struct tss_struct * tss = init_tss + smp_processor_id();
+       struct tss_struct * tss;

arch/i386/kernel/ioport.c 2002-10-06 15:21:04.000000000 -0400 line 69

Quoted 10 lines
arch/i386/kernel/ioport.c 2002-10-06 15:21:04.000000000 -0400 renamed from arch/i386/kernel/ioport.c 2002-10-06 14:58:01.000000000 -0400 +3 -0
        if ((from + num <= from) || (from + num > IO_BITMAP_SIZE*32))
                return -EINVAL;
        if (turn_on && !capable(CAP_SYS_RAWIO))
                return -EPERM;
+
+       tss = init_tss + get_cpu();
+
        /*
         * If it's the first ioperm() call in this thread's lifetime, set the
         * IO bitmap up. ioperm() is much less timing critical than clone(),

To me it really looks like you are missing a put_cpu() call somewhere. I know it is a no-op, but since you intend to show how to use it, I it really ought to be there.

Does this look right?

arch/i386/kernel/ioport.c +2 -0
diff -Nur linux.old/arch/i386/kernel/ioport.c linux.new/arch/i386/kernel/ioport.c
@@ -87,6 +87,8 @@
 	set_bitmap(t->io_bitmap, from, num, !turn_on);
 	set_bitmap(tss->io_bitmap, from, num, !turn_on);
 
+	put_cpu();
+
 	return 0;
 }
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#2 lore raw
Quoted 3 lines · Kasper Dupont

To me it really looks like you are missing a put_cpu() call somewhere. I know it is a no-op, but since you intend to show how to use it, I it really ought to be there.

Whoops, you are right.

Quoted 1 line

Does this look right?

Yep, thanks.

Marcelo, attached patch is a resend with the missing put_cpu() included. Please, apply.

Robert Love

arch/i386/kernel/ioport.c +6 -1
diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c
@@ -55,12 +55,15 @@
 asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
 {
 	struct thread_struct * t = &current->thread;
-	struct tss_struct * tss = init_tss + smp_processor_id();
+	struct tss_struct * tss;
 
 	if ((from + num <= from) || (from + num > IO_BITMAP_SIZE*32))
 		return -EINVAL;
 	if (turn_on && !capable(CAP_SYS_RAWIO))
 		return -EPERM;
+
+	tss = init_tss + get_cpu();
+
 	/*
 	 * If it's the first ioperm() call in this thread's lifetime, set the
 	 * IO bitmap up. ioperm() is much less timing critical than clone(),

@@ -84,6 +87,8 @@
 	set_bitmap(t->io_bitmap, from, num, !turn_on);
 	set_bitmap(tss->io_bitmap, from, num, !turn_on);
 
+	put_cpu();
+
 	return 0;
 }
include/linux/smp.h +6 -2
diff -urN linux-2.4.20-pre9/include/linux/smp.h linux/include/linux/smp.h
@@ -87,5 +87,9 @@
 #define smp_call_function(func,info,retry,wait)	({ 0; })
 #define cpu_online_map				1
 
-#endif
-#endif
+#endif /* !CONFIG_SMP */
+
+#define get_cpu()	smp_processor_id()
+#define put_cpu()	do { } while(0)
+
+#endif /* __LINUX_SMP_H */