[3.16.y-ckt stable] Patch "x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From dd073d97881860f45b666bbed5d9f66ac302906f Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg at redhat.com>
Date: Tue, 2 Sep 2014 19:57:17 +0200
Subject: x86, fpu: __restore_xstate_sig()->math_state_restore() needs
 preempt_disable()

commit df24fb859a4e200d9324e2974229fbb7adf00aef upstream.

Add preempt_disable() + preempt_enable() around math_state_restore() in
__restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin()
can overwrite fpu->state we are going to restore.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha at gmail.com>
Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/xsave.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index a4b451c6addf..4679ef4005da 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -399,8 +399,11 @@ int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
 			set_used_math();
 		}

-		if (use_eager_fpu())
+		if (use_eager_fpu()) {
+			preempt_disable();
 			math_state_restore();
+			preempt_enable();
+		}

 		return err;
 	} else {
--
2.1.0