On 26 Feb 2017, at 19:20, Naoya Horiguchi wrote: > On Sat, Feb 25, 2017 at 10:28:15AM +0800, Yisheng Xie wrote: >> hi Naoya, >> >> On 2017/2/23 11:23, Naoya Horiguchi wrote: >>> 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 ... >> I question about it, if a memory error happened on zero page, it will >> cause all of data read from zero page is error, I mean no-zero, right? > > Hi Yisheng, > > Yes, the impact is serious (could affect many processes,) but it's possibility > is very low because there's only one page in a system that is used for zero page. > There are many other pages which are not recoverable for memory error like > slab pages, so I'm not sure how I prioritize it (maybe it's not a > top-priority thing, nor low-hanging fruit.) > >> And can we just use re-initial it with zero data maybe by memset ? > > Maybe it's not enoguh. Under a real hwpoison, we should isolate the error > page to prevent the access on the broken data. > But zero page is statically defined as an array of global variable, so > it's not trival to replace it with a new zero page at runtime. > > Anyway, it's in my todo list, so hopefully revisited in the future. > Hi Naoya, The test case tries to HWPOISON a range of virtual addresses that do not map to any physical pages. I expected either madvise should fail because HWPOISON does not work on non-existing physical pages or madvise_hwpoison() should populate some physical pages for that virtual address range and poison them. As I tested it on kernel v4.10, the test application exited at madvise, because madvise returns -1 and error message is "Device or resource busy". I think this is a proper behavior. There might be some confusion in madvise's man page on MADV_HWPOISON. If you add some text saying madvise fails if any page is not mapped in the given address range, that can eliminate the confusion. -- Best Regards Yan Zi
Attachment:
signature.asc
Description: OpenPGP digital signature
