Re: [PATCH v1] mm: soft-offline: check return value in second __get_any_page() call

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

Sorry, I forgot to notice that this specific problem is already fixed in
mmotm with patch "mm: hwpoison: adjust for new thp refcounting", but
considering backporting to -stable, it's easier to handle this separately.

So Andrew, could you separate out the code of this patch from
"mm: hwpoison: adjust for new thp refcounting"?

Thanks,
Naoya Horiguchi

On Fri, Jan 08, 2016 at 04:22:28PM +0900, Naoya Horiguchi wrote:
> I saw the following BUG_ON triggered in a testcase where a process calls
> madvise(MADV_SOFT_OFFLINE) on thps, along with a background process that
> calls migratepages command repeatedly (doing ping-pong among different
> NUMA nodes) for the first process:
> 
>   [   52.556731] Soft offlining page 0x60000 at 0x700000600000
>   [   52.592620] __get_any_page: 0x60000 free buddy page
>   [   52.593451] page:ffffea0001800000 count:0 mapcount:-127 mapping:          (null) index:0x1
>   [   52.594767] flags: 0x1fffc0000000000()
>   [   52.595402] page dumped because: VM_BUG_ON_PAGE(atomic_read(&page->_count) == 0)
>   [   52.596602] ------------[ cut here ]------------
>   [   52.597339] kernel BUG at /src/linux-dev/include/linux/mm.h:342!
>   [   52.598284] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
>   [   52.599193] Modules linked in: cfg80211 rfkill crc32c_intel serio_raw virtio_balloon i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi
>   [   52.600579] CPU: 3 PID: 3035 Comm: test_alloc_gene Tainted: G           O    4.4.0-rc8-v4.4-rc8-160107-1501-00000-rc8+ #74
>   [   52.600579] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>   [   52.600579] task: ffff88007c63d5c0 ti: ffff88007c210000 task.ti: ffff88007c210000
>   [   52.600579] RIP: 0010:[<ffffffff8118998c>]  [<ffffffff8118998c>] put_page+0x5c/0x60
>   [   52.600579] RSP: 0018:ffff88007c213e00  EFLAGS: 00010246
>   [   52.600579] RAX: 0000000000000044 RBX: ffffea0001800000 RCX: 0000000000000000
>   [   52.600579] RDX: ffff88011f50f570 RSI: 0000000000000000 RDI: ffff88011f50cc18
>   [   52.600579] RBP: ffff88007c213e08 R08: 000000000000000a R09: 000000000000149c
>   [   52.600579] R10: ffff8800dac927f8 R11: 000000000000149c R12: ffffea0001800000
>   [   52.600579] R13: 0000000000060000 R14: ffffea0001800000 R15: 0000000000000065
>   [   52.600579] FS:  00007feb79d7d740(0000) GS:ffff88011f500000(0000) knlGS:0000000000000000
>   [   52.600579] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>   [   52.600579] CR2: 00007f3032cd2000 CR3: 00000000da6c4000 CR4: 00000000000006e0
>   [   52.600579] Stack:
>   [   52.600579]  ffffea0001800000 ffff88007c213e28 ffffffff811eb2ee ffffea0001800000
>   [   52.600579]  00000000fffffffb ffff88007c213e70 ffffffff811eccd1 0000000000000018
>   [   52.600579]  ffff88007c213e50 0000700000600000 0000700000601000 0000160000000000
>   [   52.600579] Call Trace:
>   [   52.600579]  [<ffffffff811eb2ee>] put_hwpoison_page+0x4e/0x80
>   [   52.600579]  [<ffffffff811eccd1>] soft_offline_page+0x501/0x520
>   [   52.600579]  [<ffffffff811bd18c>] SyS_madvise+0x6bc/0x6f0
>   [   52.600579]  [<ffffffff8104d0ac>] ? fpu__restore_sig+0xcc/0x320
>   [   52.600579]  [<ffffffff810a0003>] ? do_sigaction+0x73/0x1b0
>   [   52.600579]  [<ffffffff8109ceb2>] ? __set_task_blocked+0x32/0x70
>   [   52.600579]  [<ffffffff81652757>] entry_SYSCALL_64_fastpath+0x12/0x6a
>   [   52.600579] Code: 8b fc ff ff 5b 5d c3 48 89 df e8 b0 fa ff ff 48 89 df 31 f6 e8 c6 7d ff ff 5b 5d c3 48 c7 c6 08 54 a2 81 48 89 df e8 a4 c5 01 00 <0f> 0b 66 90 66 66 66 66 90 55 48 89 e5 41 55 41 54 53 48 8b 47
>   [   52.600579] RIP  [<ffffffff8118998c>] put_page+0x5c/0x60
>   [   52.600579]  RSP <ffff88007c213e00>
> 
> The root cause resides in get_any_page() which retries to get a refcount of
> the page to be soft-offlined. This function calls put_hwpoison_page(), expecting
> that the target page is putback to LRU list. But it can be also freed to buddy.
> So the second check need to care about such case.
> 
> Fixes: af8fae7c0886 ("mm/memory-failure.c: clean up soft_offline_page()")
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: stable@vger.kernel.org # v3.9+
> ---
>  mm/memory-failure.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git v4.4-rc8/mm/memory-failure.c v4.4-rc8_patched/mm/memory-failure.c
> index 8424b64..750b789 100644
> --- v4.4-rc8/mm/memory-failure.c
> +++ v4.4-rc8_patched/mm/memory-failure.c
> @@ -1572,7 +1572,7 @@ static int get_any_page(struct page *page, unsigned long pfn, int flags)
>  		 * Did it turn free?
>  		 */
>  		ret = __get_any_page(page, pfn, 0);
> -		if (!PageLRU(page)) {
> +		if (ret == 1 && !PageLRU(page)) {
>  			/* Drop page reference which is from __get_any_page() */
>  			put_hwpoison_page(page);
>  			pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
> -- 
> 1.7.1
> 
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