Re: [PATCH] mm/page_alloc: Call kernel_map_pages in unset_migrateype_isolate

[Rik van Riel <riel@redhat.com>]

On 03/16/2015 02:29 PM, Laura Abbott wrote:
> Commit 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
> changed the logic of unset_migratetype_isolate to check the buddy allocator
> and explicitly call __free_pages to merge. The page that is being freed in
> this path never had prep_new_page called so set_page_refcounted is called
> explicitly but there is no call to kernel_map_pages. With the default
> kernel_map_pages this is mostly harmless but if kernel_map_pages does any
> manipulation of the page tables (unmapping or setting pages to read only) this
> may trigger a fault:
> 
>     alloc_contig_range test_pages_isolated(ceb00, ced00) failed
>     Unable to handle kernel paging request at virtual address ffffffc0cec00000
>     pgd = ffffffc045fc4000
>     [ffffffc0cec00000] *pgd=0000000000000000
>     Internal error: Oops: 9600004f [#1] PREEMPT SMP
>     Modules linked in: exfatfs
>     CPU: 1 PID: 23237 Comm: TimedEventQueue Not tainted 3.10.49-gc72ad36-dirty #1
>     task: ffffffc03de52100 ti: ffffffc015388000 task.ti: ffffffc015388000
>     PC is at memset+0xc8/0x1c0
>     LR is at kernel_map_pages+0x1ec/0x244
> 
> Fix this by calling kernel_map_pages to ensure the page is set in the
> page table properly

Acked-by: Rik van Riel <riel@redhat.com>

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