Patchwork [1/4] powerpc: Update DSCR on all CPUs when writing sysfs dscr_default

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Submitter Anton Blanchard
Date Sept. 4, 2012, 2:47 a.m.
Message ID <20120904124756.4ddeb535@kryten>
Download mbox | patch
Permalink /patch/181483/
State Accepted, archived
Commit 1b6ca2a6fe56e7697d57348646e07df08f43b1bb
Headers show


Anton Blanchard - Sept. 4, 2012, 2:47 a.m.
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 <>  
Cc: <> # 3.0+


Index: b/arch/powerpc/kernel/sysfs.c
--- 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;