On Mon, Aug 26, 2013 at 09:34:13PM -0400, Naoya Horiguchi wrote: >On Tue, Aug 27, 2013 at 09:17:29AM +0800, Wanpeng Li wrote: >> On Mon, Aug 26, 2013 at 08:46:54PM -0400, Naoya Horiguchi wrote: >> >On Tue, Aug 27, 2013 at 08:21:05AM +0800, Wanpeng Li wrote: >> >> Hi Naoya, >> >> On Mon, Aug 26, 2013 at 08:12:29PM -0400, Naoya Horiguchi wrote: >> >> >Hi Wanpeng, >> >> > >> >> >On Tue, Aug 27, 2013 at 07:26:04AM +0800, Wanpeng Li wrote: >> >> >> Hi Naoya, >> >> >> On Mon, Aug 26, 2013 at 11:45:37AM -0400, Naoya Horiguchi wrote: >> >> >> >On Mon, Aug 26, 2013 at 04:46:12PM +0800, Wanpeng Li wrote: >> >> >> >> madvise hwpoison inject will poison the read-only empty zero page if there is >> >> >> >> no write access before poison. Empty zero page reference count will be increased >> >> >> >> for hwpoison, subsequent poison zero page will return directly since page has >> >> >> >> already been set PG_hwpoison, however, page reference count is still increased >> >> >> >> by get_user_pages_fast. The unpoison process will unpoison the empty zero page >> >> >> >> and decrease the reference count successfully for the fist time, however, >> >> >> >> subsequent unpoison empty zero page will return directly since page has already >> >> >> >> been unpoisoned and without decrease the page reference count of empty zero page. >> >> >> >> This patch fix it by decrease page reference count for empty zero page which has >> >> >> >> already been unpoisoned and page count > 1. >> >> >> > >> >> >> >I guess that fixing on the madvise side looks reasonable to me, because this >> >> >> >refcount mismatch happens only when we poison with madvise(). The root cause >> >> >> >is that we can get refcount multiple times on a page, even if memory_failure() >> >> >> >or soft_offline_page() can do its work only once. >> >> >> > >> >> >> >> >> >> I think this just happen in read-only before poison case against empty >> >> >> zero page. >> >> > >> >> >OK. I agree. >> >> > >> >> >> Hi Andrew, >> >> >> >> >> >> I see you have already merged the patch, which method you prefer? >> >> >> >> >> >> >How about making madvise_hwpoison() put a page and return immediately >> >> >> >(without calling memory_failure() or soft_offline_page()) when the page >> >> >> >is already hwpoisoned? >> >> >> >I hope it also helps us avoid meaningless printk flood. >> >> >> > >> >> >> >> >> >> Btw, Naoya, how about patch 10/10, any input are welcome! ;-) >> >> > >> >> >No objection if you (and Andrew) decide to go with current approach. >> >> >> >> Andrew prefer your method, I will resend the patch w/ your suggested-by. ;-) >> > >> >Thanks you :) >> > >> >> >But I think that if we shift to fix this problem in madvise(), >> >> >we don't need 10/10 any more. So it looks simpler to me. >> >> >> >> I don't think it's same issue. There is just one page in my test case. >> >> #define PAGES_TO_TEST 1 >> >> If I miss something? >> > >> >Ah, OK. >> >> I complete do it in madvise codes, however, the bug mentioned in patch >> 10/10 is still there. ;-) >> >> > >> >BTW, in my understanding, zero pages are not exist physically (I mean that >> >no real page is allocated to store 4096 bytes of 0.) So there can't happen >> >any real MCE SRAO on zero page. So one possible solution might be that we >> >completely ignore all of madvise(MADV_HWPOISON) over zero pages. >> >> What's the userland visible difference against mmap w/o write access before poison >> you expect? > >In this case the userland is a test program like mce-test, so my expectation >is that the test program shouldn't detect false test failures when it >accidentally calls madvise(MADV_HWPOISON) on zero pages, because there's no >real test target associated with such testcases. So I think just returning >with success return code without doing anything looks good. Ok, I will fix it in this way. ;-) Regards, Wanpeng Li > >Thanks, >Naoya Horiguchi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>