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>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/i386/xen/mmu.c b/arch/i386/xen/mmu.c
index 4ae038aa6c24..874db0cd1d2a 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);
 }