linux-kernel - [PATCH 3.10 018/123] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt

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Date:	Wed, 12 Nov 2014 10:16:24 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH 3.10 018/123] x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

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

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

From: Oleg Nesterov <oleg@...hat.com>

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@...hat.com>
Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha@...il.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/xsave.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -400,8 +400,11 @@ int __restore_xstate_sig(void __user *bu
 			set_used_math();
 		}

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

 		return err;
 	} else {

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