powerpc: Update DSCR on all CPUs when writing sysfs dscr_default

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:

http://ozlabs.org/~anton/junkcode/dscr_explicit_test.c

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index ce035c1905f0c496430b8c420d29e7fffcf0066f..0c3f9491957426483cb198dc8e804492989aaa92 100644 (file)
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -192,6 +192,12 @@ static ssize_t show_dscr_default(struct sysdev_class *class,
        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 sysdev_class *class,
                struct sysdev_class_attribute *attr, const char *buf,
                size_t count)
@@ -204,6 +210,8 @@ static ssize_t __used store_dscr_default(struct sysdev_class *class,
                return -EINVAL;
        dscr_default = val;
 
+       on_each_cpu(update_dscr, NULL, 1);
+
        return count;
 }