在 2020/9/24 上午10:06, Qian Cai 写道: > On Wed, 2020-09-23 at 15:39 +0200, Gerald Schaefer wrote: >> OK, I can now reproduce this, and unfortunately also with the gup_fast >> fix, so it is something different. Bisecting is a bit hard, as it will >> not always show immediately, sometimes takes up to an hour. >> >> Still, I think I found the culprit, merge commit b25d1dc9474e "Merge >> branch 'simplify-do_wp_page'". Without those 4 patches, it works fine, >> running over night. >> >> Not sure why this only shows on s390, should not be architecture-specific, >> but we do often see subtle races earlier than others due to hypervisor >> impact. > > Apparently, someone can reproduce something similar on x86 as well: > > https://lore.kernel.org/linux-mm/c41149a8-211e-390b-af1d-d5eee690fecb@xxxxxxxxxxxxxxxxx/ > > Probably, Alex could revert the bad commits and confirm it there. > >> >> The first commit 09854ba94c6a ("mm: do_wp_page() simplification") already yes, after revert this commit, the BUG disappears. Thanks Alex >> introduces this error. The dirtyc0w_child test seems to play with cow >> and racing madvise(MADV_DONTNEED), but I have not yet fully understood >> it and also not the changes from commit 09854ba94c6a. As Linus already >> mentioned in the merge commit message, this is some bad timing for such >> a change, so I don't want to delay this further with trying to understand >> it better before reporting. Maybe Peter or Linus can spot some obvious >> issue. >> >> One thing that seems strange to me is that the page flags from the >> bad page state output are (uptodate|swapbacked), see below, or >> (referenced|uptodate|dirty|swapbacked) in the original report. But IIUC, >> that should not qualify for the "PAGE_FLAGS_CHECK_AT_FREE flag(s) set" >> reason. So it seems that the flags have changed between check_free_page() >> and __dump_page(), which would be very odd. Or maybe some issue with >> compound pages, because __dump_page() looks at head->flags. >> >> [ 1863.237707] BUG: Bad page state in process dirtyc0w_child pfn:58527d >> [ 1863.237721] page:000000008866956b refcount:0 mapcount:0 >> mapping:0000000000000000 index:0x0 pfn:0x58527d >> [ 1863.237727] flags: 0x3ffff00000080004(uptodate|swapbacked) >> [ 1863.237734] raw: 3ffff00000080004 0000000000000100 0000000000000122 >> 0000000000000000 >> [ 1863.237738] raw: 0000000000000000 0000000000000000 ffffffff00000000 >> 0000000000000000 >> [ 1863.237742] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set >> [ 1863.237745] Modules linked in: >> [ 1863.237752] CPU: 16 PID: 9074 Comm: dirtyc0w_child Tainted: >> G B 5.9.0-rc6-00020-geff48ddeab78-dirty #104 >> [ 1863.237756] Hardware name: IBM 3906 M03 703 (LPAR) >> [ 1863.237759] Call Trace: >> [ 1863.237768] [<0000000000115f28>] show_stack+0x100/0x158 >> [ 1863.237775] [<000000000096b41a>] dump_stack+0xa2/0xd8 >> [ 1863.237781] [<00000000003d497c>] bad_page+0xdc/0x140 >> [ 1863.237785] [<00000000003d5b62>] free_pcp_prepare+0x31a/0x360 >> [ 1863.237789] [<00000000003d906a>] free_unref_page+0x32/0xb8 >> [ 1863.237794] [<00000000003b05f4>] zap_p4d_range+0x64c/0xcf8 >> [ 1863.237797] [<00000000003b0e7a>] unmap_page_range+0x9a/0x110 >> [ 1863.237801] [<00000000003b0f84>] unmap_single_vma+0x94/0x100 >> [ 1863.237805] [<00000000003b14c2>] zap_page_range+0x14a/0x1f0 >> [ 1863.237809] [<00000000003e3a24>] do_madvise+0x75c/0x918 >> [ 1863.237812] [<00000000003e3c06>] __s390x_sys_madvise+0x26/0x38 >> [ 1863.237817] [<0000000000d280d4>] system_call+0xe0/0x2c0 >> [ 1863.237820] INFO: lockdep is turned off. >>
