linux-kernel - [ 038/135] powerpc: Fix DSCR inheritance in copy

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Message-Id: <20120917003631.514835802@decadent.org.uk>
Date:	Mon, 17 Sep 2012 01:37:03 +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: [ 038/135] powerpc: Fix DSCR inheritance in copy_thread()

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

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

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

commit 1021cb268b3025573c4811f1dee4a11260c4507b upstream.

If the default DSCR is non zero we set thread.dscr_inherit in
copy_thread() meaning the new thread and all its children will ignore
future updates to the default DSCR. This is not intended and is
a change in behaviour that a number of our users have hit.

We just need to inherit thread.dscr and thread.dscr_inherit from
the parent which ends up being much simpler.

This was found with the following test case:

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

Signed-off-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/kernel/process.c |   12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 710f400..1a1f2dd 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -802,16 +802,8 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 #endif /* CONFIG_PPC_STD_MMU_64 */
 #ifdef CONFIG_PPC64 
 	if (cpu_has_feature(CPU_FTR_DSCR)) {
-		if (current->thread.dscr_inherit) {
-			p->thread.dscr_inherit = 1;
-			p->thread.dscr = current->thread.dscr;
-		} else if (0 != dscr_default) {
-			p->thread.dscr_inherit = 1;
-			p->thread.dscr = dscr_default;
-		} else {
-			p->thread.dscr_inherit = 0;
-			p->thread.dscr = 0;
-		}
+		p->thread.dscr_inherit = current->thread.dscr_inherit;
+		p->thread.dscr = current->thread.dscr;
 	}
 #endif
 


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