linux-kernel - Re: Xen kernel 2.6.23-rc7 bug at xen_mc_flush (arch/i386/xen/multicalls.c:68)

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Date:	Mon, 24 Sep 2007 17:43:30 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	osth@...esurf.ch
CC:	linux-kernel@...r.kernel.org
Subject: Re: Xen kernel 2.6.23-rc7 bug at xen_mc_flush (arch/i386/xen/multicalls.c:68)

osth@...esurf.ch wrote:
> Using kernel 2.6.23-rc7 as xen domU client system I observe a kernel bug
> which occurs reproducibly when calling a shell from midnight commander F2
> context menu or with testcase given below  (However most other programs seem
> to
> be well behaved and do not trigger this bug). - A kernel compiled with debug
> info gives:
>   

Hm, it just seems that its trying to unpin an mm on the error path of
execve, and so it hasn't been pinned.  The simplest way to reproduce is:

$ echo foo > foo
$ chmod +x foo
$ ./foo

Anyway, try this patch.

    J

---
 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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