linux-kernel - [ 036/135] powerpc: Update DSCR on all CPUs when writing sysfs dscr

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Message-Id: <20120917003631.247940408@decadent.org.uk>
Date:	Mon, 17 Sep 2012 01:37:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Anton Blanchard <anton@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [ 036/135] powerpc: Update DSCR on all CPUs when writing sysfs dscr_default

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

------------------

From: Anton Blanchard <anton@...ba.org>

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@...ba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/kernel/sysfs.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -192,6 +192,12 @@ 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 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
 		return -EINVAL;
 	dscr_default = val;
 
+	on_each_cpu(update_dscr, NULL, 1);
+
 	return count;
 }
 


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