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Subject[ 078/108] powerpc: Update DSCR on all CPUs when writing sysfs dscr_default
From: Greg KH <>

3.5-stable review patch. If anyone has any objections, please let me know.


From: Anton Blanchard <>

commit 1b6ca2a6fe56e7697d57348646e07df08f43b1bb upstream.

Writing to dscr_default in sysfs doesn't actually change the DSCR -
we rely on a context switch on each CPU to do the work. There is no
guarantee we will get a context switch in a reasonable amount of time
so fire off an IPI to force an immediate change.

This issue was found with the following test case:

Signed-off-by: Anton Blanchard <>
Signed-off-by: Benjamin Herrenschmidt <>
Signed-off-by: Greg Kroah-Hartman <>

arch/powerpc/kernel/sysfs.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -194,6 +194,12 @@ static ssize_t show_dscr_default(struct
return sprintf(buf, "%lx\n", dscr_default);

+static void update_dscr(void *dummy)
+ if (!current->thread.dscr_inherit)
+ mtspr(SPRN_DSCR, dscr_default);
static ssize_t __used store_dscr_default(struct device *dev,
struct device_attribute *attr, const char *buf,
size_t count)
@@ -206,6 +212,8 @@ static ssize_t __used store_dscr_default
return -EINVAL;
dscr_default = val;

+ on_each_cpu(update_dscr, NULL, 1);
return count;

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