From: Oleg Nesterov <oleg@redhat.com>
Date: Sun, 7 Feb 2010 18:11:15 -0500
Subject: [x86_64] fix floating point state corruption after signal
Message-id: <20100207181115.GA12449@redhat.com>
Patchwork-id: 23172
O-Subject: [RHEL5 PATCH] BZ#560891: x86_64: floating point state corruption
	after handling the signal
Bugzilla: 560891
RH-Acked-by: Zachary Amsden <zamsden@redhat.com>
RH-Acked-by: Doug Ledford <dledford@redhat.com>

https://bugzilla.redhat.com/show_bug.cgi?id=560891

This patch is simplified version of
https://bugzilla.redhat.com/attachment.cgi?id=378651
from chuck.anderson@oracle.com

Upstream status: the patched code matches upstream, but I failed to find
the patch which does this change, there were to many renames.

We must never clear PF_USED_MATH before we save FPU registers. Otherwise,
if we get a preemption in between, math_state_restore() will reinitialize
the FPU state when the task is scheduled again, before fxsave actually
save it.

Change save_i387() to clear PF_USED_MATH after we saved the FPU state.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/arch/x86_64/kernel/i387.c b/arch/x86_64/kernel/i387.c
index 3aa1e9b..51d2329 100644
--- a/arch/x86_64/kernel/i387.c
+++ b/arch/x86_64/kernel/i387.c
@@ -93,17 +93,17 @@ int save_i387(struct _fpstate __user *buf)
 
 	if (!used_math())
 		return 0;
-	clear_used_math(); /* trigger finit */
 	if (task_thread_info(tsk)->status & TS_USEDFPU) {
 		err = save_i387_checking((struct i387_fxsave_struct __user *)buf);
 		if (err) return err;
 		stts();
-		} else {
+	} else {
 		if (__copy_to_user(buf, &tsk->thread.i387.fxsave, 
 				   sizeof(struct i387_fxsave_struct)))
 			return -1;
 	} 
-		return 1;
+	clear_used_math(); /* trigger finit */
+	return 1;
 }
 
 /*