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SubjectRe: [PATCH 00/10] Hwpoison soft-offline rework
Date
Hi Oscar,

Thank you for your working on this.

My testing shows the following error:

[ 1926.932435] ===> testcase 'mce_ksm_soft-offline_avoid_access.auto2' start
[ 1927.155321] bash (15853): drop_caches: 3
[ 1929.019094] page:ffffe5c384c4cd40 refcount:1 mapcount:0 mapping:0000000000000003 index:0x700000001
[ 1929.021586] anon
[ 1929.021588] flags: 0x57ffe00088000e(referenced|uptodate|dirty|swapbacked|hwpoison)
[ 1929.024289] raw: 0057ffe00088000e dead000000000100 dead000000000122 0000000000000003
[ 1929.026611] raw: 0000000700000001 0000000000000000 00000000ffffffff 0000000000000000
[ 1929.028760] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page))
[ 1929.030559] ------------[ cut here ]------------
[ 1929.031684] kernel BUG at mm/internal.h:73!
[ 1929.032738] invalid opcode: 0000 [#1] SMP PTI
[ 1929.033941] CPU: 3 PID: 16052 Comm: mceinj.sh Not tainted 5.3.0-rc8-v5.3-rc8-190911-1025-00010-ga436dbce8674+ #18
[ 1929.037137] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
[ 1929.040066] RIP: 0010:page_set_poison+0xf9/0x160
[ 1929.041665] Code: 63 02 7f 31 c0 5b 5d 41 5c c3 48 c7 c6 d0 d1 0c b0 48 89 df e8 88 bb f8 ff 0f 0b 48 c7 c6 f0 2a 0d b0 48 89 df e8 77 bb f8 ff <0f> 0b 48 8b 45 00 48 c1 e8 33 83 e0 07 83 f8 04 75 89 48 8b 45 08
[ 1929.047773] RSP: 0018:ffffb4fb8a73bde0 EFLAGS: 00010246
[ 1929.049511] RAX: 0000000000000039 RBX: ffffe5c384c4cd40 RCX: 0000000000000000
[ 1929.051870] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffb00d1814
[ 1929.054238] RBP: ffffe5c384c4cd40 R08: 0000000000000596 R09: 0000000000000048
[ 1929.056599] R10: 0000000000000000 R11: ffffb4fb8a73bc58 R12: 0000000000000000
[ 1929.058986] R13: ffffb4fb8a73be10 R14: 0000000000131335 R15: 0000000000000001
[ 1929.061366] FS: 00007fc9e208d740(0000) GS:ffff9fa9bdb00000(0000) knlGS:0000000000000000
[ 1929.063842] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1929.065429] CR2: 000055946c05d192 CR3: 00000001365f2000 CR4: 00000000001406e0
[ 1929.067373] Call Trace:
[ 1929.068094] soft_offline_page+0x2be/0x600
[ 1929.069246] soft_offline_page_store+0xdf/0x110
[ 1929.070510] kernfs_fop_write+0x116/0x190
[ 1929.071618] vfs_write+0xa5/0x1a0
[ 1929.072614] ksys_write+0x59/0xd0
[ 1929.073548] do_syscall_64+0x5f/0x1a0
[ 1929.074554] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 1929.075957] RIP: 0033:0x7fc9e217ded8

It seems that soft-offlining on ksm pages is affected by this changeset.
Could you try to handle this?

- Naoya

On Tue, Sep 10, 2019 at 12:30:06PM +0200, Oscar Salvador wrote:
>
> This patchset was based on Naoya's hwpoison rework [1], so thanks to him
> for the initial work.
>
> This patchset aims to fix some issues laying in soft-offline handling,
> but it also takes the chance and takes some further steps to perform
> cleanups and some refactoring as well.
>
> - Motivation:
>
> A customer and I were facing an issue where poisoned pages we returned
> back to user-space after having offlined them properly.
> This was only seend under some memory stress + soft offlining pages.
> After some anaylsis, it became clear that the problem was that
> when kcompactd kicked in to migrate pages over, compaction_alloc
> callback was handing poisoned pages to the migrate routine.
> Once this page was later on fault in, __do_page_fault returned
> VM_FAULT_HWPOISON making the process being killed.
>
> All this could happen because isolate_freepages_block and
> fast_isolate_freepages just check for the page to be PageBuddy,
> and since 1) poisoned pages can be part of a higher order page
> and 2) poisoned pages are also Page Buddy, they can sneak in easily.
>
> I also saw some problem with swap pages, but I suspected to be the
> same sort of problem, so I did not follow that trace.
>
> The full explanation can be see in [2].
>
> - Approach:
>
> The taken approach is to not let poisoned pages hit neither
> pcplists nor buddy freelists.
> This is achieved by:
>
> In-use pages:
>
> * Normal pages
>
> 1) do not release the last reference count after the
> invalidation/migration of the page.
> 2) the page is being handed to page_set_poison, which does:
> 2a) sets PageHWPoison flag
> 2b) calls put_page (only to be able to call __page_cache_release)
> Since poisoned pages are skipped in free_pages_prepare,
> this put_page is safe.
> 2c) Sets the refcount to 1
>
> * Hugetlb pages
>
> 1) Hand the page to page_set_poison after migration
> 2) page_set_poison does:
> 2a) Calls dissolve_free_huge_page
> 2b) If ranged to be dissolved contains poisoned pages,
> we free the rangeas order-0 pages (as we do with gigantic hugetlb page),
> so free_pages_prepare will skip them accordingly.
> 2c) Sets the refcount to 1
>
> Free pages:
>
> * Normal pages:
>
> 1) Take the page off the buddy freelist
> 2) Set PageHWPoison flag and set refcount to 1
>
> * Hugetlb pages
>
> 1) Try to allocate a new hugetlb page to the pool
> 2) Take off the pool the poisoned hugetlb
>
>
> With this patchset, I no longer see the issues I faced before.
>
> Note:
> I presented this as RFC to open discussion of the taken aproach.
> I think that furthers cleanups and refactors could be made, but I would
> like to get some insight of the taken approach before touching more
> code.
>
> Thanks
>
> [1] https://lore.kernel.org/linux-mm/1541746035-13408-1-git-send-email-n-horiguchi@ah.jp.nec.com/
> [2] https://lore.kernel.org/linux-mm/20190826104144.GA7849@linux/T/#u
>
> Naoya Horiguchi (5):
> mm,hwpoison: cleanup unused PageHuge() check
> mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
> mm,hwpoison-inject: don't pin for hwpoison_filter
> mm,hwpoison: remove MF_COUNT_INCREASED
> mm: remove flag argument from soft offline functions
>
> Oscar Salvador (5):
> mm,hwpoison: Unify THP handling for hard and soft offline
> mm,hwpoison: Rework soft offline for in-use pages
> mm,hwpoison: Refactor soft_offline_huge_page and __soft_offline_page
> mm,hwpoison: Rework soft offline for free pages
> mm,hwpoison: Use hugetlb_replace_page to replace free hugetlb pages
>
> drivers/base/memory.c | 2 +-
> include/linux/mm.h | 9 +-
> include/linux/page-flags.h | 5 -
> mm/hugetlb.c | 51 +++++++-
> mm/hwpoison-inject.c | 18 +--
> mm/madvise.c | 25 ++--
> mm/memory-failure.c | 319 +++++++++++++++++++++------------------------
> mm/migrate.c | 11 +-
> mm/page_alloc.c | 62 +++++++--
> 9 files changed, 267 insertions(+), 235 deletions(-)
>
> --
> 2.12.3
>
>

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