Re: [PATCH] mm: fix pfn spans two sections in has_unmovable_pages()

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

On Mon, May 09, 2016 at 06:02:32PM +0800, Xishi Qiu wrote:
> On 2016/5/9 17:39, Vlastimil Babka wrote:
> 
> > On 05/09/2016 10:34 AM, Xishi Qiu wrote:
> >> If the pfn is not aligned to pageblock, the check pfn may access a next
> >> pageblcok, and the next pageblock may belong to a next section. Because
> >> struct page has not been alloced in the next section, so kernel panic.
> >>
> >> I find the caller of has_unmovable_pages() has passed a aligned pfn, so it
> >> doesn't have this problem. But the earlier kernel version(e.g. v3.10) has.
> >> e.g. echo xxx > /sys/devices/system/memory/soft_offline_page could trigger
> >> it. The following log is from RHEL v7.1
> > 
> > I think has_unmovable_pages() is wrong layer where to fix such problem, as I'll explain below.
> > 
> >> [14111.611492] Stack:
> >> [14111.611494] ffffffff8115d952 0000000000000000 01ff880c393ebe40 ffff880c7ffd9000
> >> [14111.611500] ffffea0061ffffc0 ffff880c7ffd9068 0000000000000286 0000000000000001
> >> [14111.611505] ffff880c393ebe10 ffffffff811c265a 000000000187ffff 0000000000000200
> >> [14111.611511] Call Trace:
> >> [14111.611516] [<ffffffff8115d952>] ? has_unmovable_pages+0xd2/0x130
> >> [14111.611521] [<ffffffff811c265a>] set_migratetype_isolate+0xda/0x170
> >> [14111.611526] [<ffffffff811c187a>] soft_offline_page+0x9a/0x590
> >> [14111.611530] [<ffffffff812e7cab>] ? _kstrtoull+0x3b/0xa0
> >> [14111.611535] [<ffffffff813e158f>] store_soft_offline_page+0xaf/0xf0
> >> [14111.611539] [<ffffffff813cae18>] dev_attr_store+0x18/0x30
> >> [14111.611544] [<ffffffff8123c046>] sysfs_write_file+0xc6/0x140
> >> [14111.611548] [<ffffffff811c5b5d>] vfs_write+0xbd/0x1e0
> >> [14111.611551] [<ffffffff811c65a8>] SyS_write+0x58/0xb0
> >> [14111.611556] [<ffffffff8160f509>] system_call_fastpath+0x16/0x1b
> >> [14111.611559] Code: 66 66 66 90 48 83 e0 fd 0c a0 5d c3 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 66 66 66 90 48 83 c8 42 0c a0 5d c3 90 66 66 66 66 90 <8b> 07 25 00 c0 00 00 75 02 f3 c3 48 8b 07 f6 c4 80 75 0f 48 81
> >> [14111.611594] RIP [<ffffffff81199fc5>] PageHuge+0x5/0x40
> >> [14111.611598] RSP <ffff880c393ebd80>
> >> [14111.611600] CR2: ffffea0062000000
> >> [14111.611604] ---[ end trace 9f780ed1def334c6 ]---
> >> [14111.678586] Kernel panic - not syncing: Fatal exception
> >>
> >> Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
> > 
> > It's not CC'd stable, so how will this patch fix the older kernels? Also you should determine which upstream kernel versions are affected, not a RHEL derivative.
> > Also is the current upstream broken or not?
> > 
> 
> OK, I'll resend it later. The current upstream has not this problem.

This is because soft offline has stopped changing migratetype at commit
add05cecef80 ("mm: soft-offline: don't free target page in successful
page migration") (or v4.1-3344-gadd05cecef80).
# And the fix is available in RHEL7.2, but unfortunately not in RHEL7.1.

Thanks,
Naoya Horiguchi
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