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
diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c
--- linux-2.4.20-pre9/arch/i386/kernel/ioport.c 2002-10-06 14:58:01.000000000 -0400
+++ linux/arch/i386/kernel/ioport.c 2002-10-06 15:21:04.000000000 -0400
@@ -55,12 +55,15 @@
asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
struct thread_struct * t = ¤t->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(),
diff -urN linux-2.4.20-pre9/include/linux/smp.h linux/include/linux/smp.h
--- linux-2.4.20-pre9/include/linux/smp.h 2002-10-06 14:57:20.000000000 -0400
+++ linux/include/linux/smp.h 2002-10-06 15:11:00.000000000 -0400
@@ -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 */
Robert Love wrote:
>
> diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c
> --- linux-2.4.20-pre9/arch/i386/kernel/ioport.c 2002-10-06 14:58:01.000000000 -0400
> +++ linux/arch/i386/kernel/ioport.c 2002-10-06 15:21:04.000000000 -0400
> @@ -55,12 +55,15 @@
> asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
> {
> struct thread_struct * t = ¤t->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(),
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?
diff -Nur linux.old/arch/i386/kernel/ioport.c linux.new/arch/i386/kernel/ioport.c
--- linux.old/arch/i386/kernel/ioport.c Sun Oct 6 22:33:22 2002
+++ linux.new/arch/i386/kernel/ioport.c Sun Oct 6 22:33:53 2002
@@ -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;
}
--
Kasper Dupont -- der bruger for meget tid p? usenet.
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or mailto:[email protected]
On Sun, 2002-10-06 at 16:36, Kasper Dupont wrote:
> 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.
> Does this look right?
Yep, thanks.
Marcelo, attached patch is a resend with the missing put_cpu()
included. Please, apply.
Robert Love
diff -urN linux-2.4.20-pre9/arch/i386/kernel/ioport.c linux/arch/i386/kernel/ioport.c
--- linux-2.4.20-pre9/arch/i386/kernel/ioport.c 2002-10-06 14:58:01.000000000 -0400
+++ linux/arch/i386/kernel/ioport.c 2002-10-06 16:53:04.000000000 -0400
@@ -55,12 +55,15 @@
asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
struct thread_struct * t = ¤t->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;
}
diff -urN linux-2.4.20-pre9/include/linux/smp.h linux/include/linux/smp.h
--- linux-2.4.20-pre9/include/linux/smp.h 2002-10-06 14:57:20.000000000 -0400
+++ linux/include/linux/smp.h 2002-10-06 16:52:45.000000000 -0400
@@ -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 */