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 <[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED]

---
 arch/i386/xen/mmu.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

===================================================================
--- a/arch/i386/xen/mmu.c
+++ b/arch/i386/xen/mmu.c
@@ -558,6 +558,9 @@ 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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