Re: [Xen-devel] [PATCH 5/5] mm: Don't hold heap lock in alloc_heap_pages() longer than necessary

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Aug 30, 2017 at 08:59:34AM -0400, Boris Ostrovsky wrote:
> 
> >> This patch has been applied to staging, but its got problems.  The
> >> following crash is rather trivial to provoke:
> >>
> >> ~Andrew
> >>
> >> (d19) Test result: SUCCESS
> >> (XEN) ----[ Xen-4.10-unstable  x86_64  debug=y   Tainted:    H ]----
> >> (XEN) CPU:    5
> >> (XEN) RIP:    e008:[<ffff82d0802252fc>] 
> >> page_alloc.c#free_heap_pages+0x786/0x7a1
> >> ...
> >> (XEN) Pagetable walk from ffff82ffffffffe4:
> >> (XEN)  L4[0x105] = 00000000abe5b063 ffffffffffffffff
> >> (XEN)  L3[0x1ff] = 0000000000000000 ffffffffffffffff
> > Some negative offset into somewhere, it seems. Upon second
> > look I think the patch is simply wrong in its current shape:
> > free_heap_pages() looks for page_state_is(..., free) when
> > trying to merge chunks, while alloc_heap_pages() now sets
> > PGC_state_inuse outside of the locked area. I'll revert it right
> > away.
> 
> Yes, so we do need to update page state under heap lock. I'll then move
> scrubbing (and checking) only to outside the lock.
> 
> I am curious though, what was the test to trigger this? I ran about 100
> parallel reboots under memory pressure and never hit this.
> 

Appears to be one of the tests in xtf.git

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