Re: [Xen-devel] balloon_mutex lockdep complaint at HVM domain destroy

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 25/05/16 15:30, Ed Swierk wrote:
> The following lockdep dump occurs whenever I destroy an HVM domain, on
> Linux 4.4 Dom0 with CONFIG_XEN_BALLOON=n on recent stable Xen 4.5.

This occurs in dom0?  Or the guest that's being destroyed?

> Any clues whether this is a real potential deadlock, or how to silence
> it if not?

It's a bug but...

> ======================================================
> [ INFO: RECLAIM_FS-safe -> RECLAIM_FS-unsafe lock order detected ]
> 4.4.11-grsec #1 Not tainted
  ^^^^^^^^^^^^
...this isn't a vanilla kernel?  Can you try vanilla 4.6?

Because:

>    IN-RECLAIM_FS-W at:
>                        [<__lock_acquire at lockdep.c:2839>] ffffffff810becc5
>                        [<lock_acquire at paravirt.h:839>] ffffffff810c0ac9
>                        [<mutex_lock_nested at mutex.c:526>] ffffffff816d1b4c
>                        [<mn_invl_range_start at gntdev.c:476>] 
> ffffffff8143c3d4
>                        [<mn_invl_page at gntdev.c:490>] ffffffff8143c450
>                        [<__mmu_notifier_invalidate_page at 
> mmu_notifier.c:183>] ffffffff8119de42
>                        [<try_to_unmap_one at mmu_notifier.h:275>] 
> ffffffff811840c2
>                        [<rmap_walk at rmap.c:1689>] ffffffff81185051
>                        [<try_to_unmap at rmap.c:1534>] ffffffff81185497
>                        [<shrink_page_list at vmscan.c:1063>] ffffffff811599b7
>                        [<shrink_inactive_list at spinlock.h:339>] 
> ffffffff8115a489
>                        [<shrink_lruvec at vmscan.c:1942>] ffffffff8115af3a
>                        [<shrink_zone at vmscan.c:2411>] ffffffff8115b1bb
>                        [<kswapd at vmscan.c:3116>] ffffffff8115c1e4
>                        [<kthread at kthread.c:209>] ffffffff8108eccc
>                        [<ret_from_fork at entry_64.S:890>] ffffffff816d706e

We should not be reclaiming pages from a gntdev VMA since it's special
(marked as VM_IO).

David

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