linux-kernel - [PATCH] xen: execve's error paths don't pin the mm before unpinning

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Date:	Tue, 25 Sep 2007 11:50:00 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, osth@...esurf.ch
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@...source.com>
Cc: osth@...esurf.ch

---
 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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