Re: [PATCH] mm: hwpoison: Use compound_head() flags for huge pages

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Wed, May 24, 2017 at 02:02:04PM +0100, James Morse wrote:
> memory_failure() chooses a recovery action function based on the page
> flags. For huge pages it uses the tail page flags which don't have
> anything interesting set, resulting in:
> > Memory failure: 0x9be3b4: Unknown page state
> > Memory failure: 0x9be3b4: recovery action for unknown page: Failed
> 
> Instead, save a copy of the head page's flags if this is a huge page,
> this means if there are no relevant flags for this tail page, we use
> the head pages flags instead. This results in the me_huge_page()
> recovery action being called:
> > Memory failure: 0x9b7969: recovery action for huge page: Delayed
> 
> For hugepages that have not yet been allocated, this allows the hugepage
> to be dequeued.
> 
> CC: Punit Agrawal <punit.agrawal@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>

Looks good to me.

Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

> ---
> This is intended as a fix, but I can't find the patch that introduced this
> behaviour. (not recent, and there is a lot of history down there!)

Please add a tag

Fixes: 524fca1e7356 ("HWPOISON: fix misjudgement of page_action() for errors on mlocked pages")

> 
> This doesn't apply to stable trees before v3.10...
> Cc: stable@vger.kernel.org # 3.10.105

You can skip older stable kernels to which the fix isn't cleanly applicable.

Thanks,
Naoya Horiguchi

> 
>  mm/memory-failure.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 2527dfeddb00..44a6a33af219 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1184,7 +1184,10 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
>  	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
>  	 * correctly, we save a copy of the page flags at this time.
>  	 */
> -	page_flags = p->flags;
> +	if (PageHuge(p))
> +		page_flags = hpage->flags;
> +	else
> +		page_flags = p->flags;
>  
>  	/*
>  	 * unpoison always clear PG_hwpoison inside page lock
> -- 
> 2.11.0
> 
> 
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