Re: Is MADV_HWPOISON supposed to work only on faulted-in pages?

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

On Mon, Feb 20, 2017 at 05:00:17AM +0000, Horiguchi Naoya(堀口 直也) wrote:
> On Tue, Feb 14, 2017 at 04:41:29PM +0100, Jan Stancek wrote:
> > Hi,
> >
> > code below (and LTP madvise07 [1]) doesn't produce SIGBUS,
> > unless I touch/prefault page before call to madvise().
> >
> > Is this expected behavior?
> 
> Thank you for reporting.
> 
> madvise(MADV_HWPOISON) triggers page fault when called on the address
> over which no page is faulted-in, so I think that SIGBUS should be
> called in such case.
> 
> But it seems that memory error handler considers such a page as "reserved
> kernel page" and recovery action fails (see below.)
> 
>   [  383.371372] Injecting memory failure for page 0x1f10 at 0x7efcdc569000
>   [  383.375678] Memory failure: 0x1f10: reserved kernel page still referenced by 1 users
>   [  383.377570] Memory failure: 0x1f10: recovery action for reserved kernel page: Failed
> 
> I'm not sure how/when this behavior was introduced, so I try to understand.

I found that this is a zero page, which is not recoverable for memory
error now.

> IMO, the test code below looks valid to me, so no need to change.

I think that what the testcase effectively does is to test whether memory
handling on zero pages works or not.
And the testcase's failure seems acceptable, because it's simply not-implemented yet.
Maybe recovering from error on zero page is possible (because there's no data
loss for memory error,) but I'm not sure that code might be simple enough and/or
it's worth doing ...

Thanks,
Naoya Horiguchi
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