Re: [Xen-devel] Xen 4.7 crash

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/06/2016 20:54, Aaron Cornelius wrote:
> <snip>
> (XEN) Xen call trace:
> (XEN)    [<0021fdd4>] free_domheap_pages+0x1c/0x324 (PC)
> (XEN)    [<0025b0cc>] p2m_teardown+0xa0/0x108 (LR)
> (XEN)    [<0025b0cc>] p2m_teardown+0xa0/0x108
> (XEN)    [<0024f668>] arch_domain_destroy+0x20/0x50
> (XEN)    [<0024f8f0>] arch_domain_create+0x258/0x284
> (XEN)    [<0020854c>] domain_create+0x2dc/0x510
> (XEN)    [<00206d6c>] do_domctl+0x5b4/0x1928
> (XEN)    [<00260130>] do_trap_hypervisor+0x1170/0x15b0
> (XEN)    [<00263b10>] entry.o#return_from_trap+0/0x4
> (XEN)
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) CPU0: Unexpected Trap: Data Abort
> (XEN)
> (XEN) ****************************************
> (XEN)
> (XEN) Reboot in five seconds...

As for this specific crash itself,  In the case of an early error path,
p2m->root can be NULL in p2m_teardown(), in which case
free_domheap_pages() will fall over in a heap.  This patch should
resolve it.

@@ -1408,7 +1411,8 @@ void p2m_teardown(struct domain *d)
     while ( (pg = page_list_remove_head(&p2m->pages)) )
         free_domheap_page(pg);

-    free_domheap_pages(p2m->root, P2M_ROOT_ORDER);
+    if ( p2m->root )
+        free_domheap_pages(p2m->root, P2M_ROOT_ORDER);

     p2m->root = NULL;

I would be tempted to suggest making free_domheap_pages() tolerate NULL
pointers, except that would only be a safe thing to do if we assert that
the order parameter is 0, which won't help this specific case.

~Andrew

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