From df912ea4ae7233d1504fbd861ee127bd7ee5781d Mon Sep 17 00:00:00 2001
From: Jeremy Fitzhardinge <jeremy@goop.org>
Date: Tue, 25 Sep 2007 11:50:00 -0700
Subject: [PATCH] xen: execve's error paths don't pin the mm before unpinning

execve's error paths don't activate (and therefore pin) the mm before
calling exit_mmap to free it up, so don't try to unpin unless it is
actually pinned.  This prevents a BUG_ON from triggering.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Christian Ostheimer <osth@freesurf.ch>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/i386/xen/mmu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/i386/xen/mmu.c b/arch/i386/xen/mmu.c
index 4ae038aa6c244..874db0cd1d2a5 100644
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -559,6 +559,9 @@ void xen_exit_mmap(struct mm_struct *mm)
 	put_cpu();
 
 	spin_lock(&mm->page_table_lock);
-	xen_pgd_unpin(mm->pgd);
+
+	/* pgd may not be pinned in the error exit path of execve */
+	if (PagePinned(virt_to_page(mm->pgd)))
+		xen_pgd_unpin(mm->pgd);
 	spin_unlock(&mm->page_table_lock);
 }
-- 
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