From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>,
Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: akpm@linux-foundation.org, osalvador@suse.de,
dan.j.williams@intel.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section
Date: Wed, 24 Jun 2020 09:48:43 +0200 [thread overview]
Message-ID: <57d8a558-dcb3-b318-8e38-6c016b050414@redhat.com> (raw)
In-Reply-To: <20200623151828.GA31426@dhcp22.suse.cz>
On 23.06.20 17:18, Michal Hocko wrote:
> On Tue 23-06-20 17:42:58, Wei Yang wrote:
>> For early sections, we assumes its memmap will never be partially
>> removed. But current behavior breaks this.
>>
>> Let's correct it.
>>
>> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
>
> Can a user trigger this or is this a theoretical bug?
I tried to reproduce it, but somehow I get unexpected behavior.
With a hacked QEMU I can get
$ cat /proc/iomem
[...]
100000000-143ffffff : System RAM
144000000-343dfffff : Persistent Memory
144000000-1441fffff : namespace0.0
144200000-144ffffff : dax0.0
After
$ ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M
I get
$ cat /proc/iomem
[...]
100000000-143ffffff : System RAM
144000000-343dfffff : Persistent Memory
144000000-1441fffff : namespace0.0
144200000-144ffffff : dax0.0
I can trigger remove+re-add via
$ ndctl create-namespace --force --reconfig=namespace0.0 --mode=devdax --size=16M
So we clearly have an overlap between System RAM and dax0.0 within a section.
However, I never get early_section() to trigger in
section_activate()/section_deactivate() ? That's unexpected
Definitely something seems to go wrong after the first "ndctl create-namespace".
Using a random page walker:
[root@localhost ~]# ./page-types
[ 387.019229] general protection fault, probably for non-canonical address 0xfdfdfdfdfdfdfdfc: 0000 [#1] SMP NOPTI
[ 387.020172] CPU: 17 PID: 1314 Comm: page-types Kdump: loaded Tainted: G W 5.8.0-rc2 #20
[ 387.021015] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.4
[ 387.022056] RIP: 0010:stable_page_flags+0x27/0x3f0
[ 387.022519] Code: 00 00 00 66 66 66 66 90 48 85 ff 0f 84 d2 03 00 00 41 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48f
[ 387.024291] RSP: 0018:ffff9f8781057e58 EFLAGS: 00010202
[ 387.024775] RAX: fdfdfdfdfdfdfdfc RBX: fdfdfdfdfdfdfdfd RCX: 00007ffc4f4f1f78
[ 387.025423] RDX: 0000000000000001 RSI: 0000002000000000 RDI: ffffc590c5100000
[ 387.026052] RBP: ffffc590c5100000 R08: 0000000000000001 R09: 0000000000000000
[ 387.026696] R10: 0000000000000000 R11: 0000000000000000 R12: 00007ffc4f4f1f80
[ 387.027324] R13: 0000000000040000 R14: 00007ffc4f4d1f80 R15: ffffffffa1577ee0
[ 387.027974] FS: 00007f91a0f9c580(0000) GS:ffff888b3f7c0000(0000) knlGS:0000000000000000
[ 387.028699] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 387.029223] CR2: 0000000000449b00 CR3: 000000007a7fc000 CR4: 00000000000006e0
[ 387.029864] Call Trace:
[ 387.030108] kpageflags_read+0xcc/0x160
[ 387.030473] proc_reg_read+0x53/0x80
[ 387.030809] vfs_read+0x9d/0x150
[ 387.031114] ksys_pread64+0x65/0xa0
[ 387.031449] do_syscall_64+0x4d/0x90
[ 387.031783] entry_SYSCALL_64_after_hwframe+0x44/0xa9
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-06-24 7:48 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 9:42 Wei Yang
2020-06-23 12:44 ` David Hildenbrand
2020-06-23 13:02 ` Wei Yang
2020-06-23 13:16 ` David Hildenbrand
2020-06-23 15:18 ` Michal Hocko
2020-06-23 21:48 ` Wei Yang
2020-06-24 6:13 ` Wei Yang
2020-06-24 16:10 ` Dan Williams
2020-06-24 22:05 ` Wei Yang
2020-06-24 22:20 ` Dan Williams
2020-06-24 22:44 ` Wei Yang
2020-06-24 23:47 ` Dan Williams
2020-06-25 5:53 ` David Hildenbrand
2020-06-25 19:46 ` Dan Williams
2020-06-25 22:29 ` Wei Yang
2020-06-29 8:34 ` Wei Yang
2020-06-29 22:13 ` Dan Williams
2020-06-29 22:58 ` Wei Yang
2020-06-30 7:16 ` David Hildenbrand
2020-06-25 22:39 ` Wei Yang
2020-06-26 4:59 ` David Hildenbrand
2020-06-24 7:48 ` David Hildenbrand [this message]
2020-06-24 8:04 ` David Hildenbrand
2020-06-24 8:13 ` Wei Yang
2020-06-24 8:41 ` David Hildenbrand
2020-06-24 8:50 ` Michal Hocko
2020-06-24 22:27 ` Wei Yang
2020-06-24 0:21 ` Dan Williams
2020-06-24 1:11 ` Wei Yang
2020-06-24 1:47 ` Baoquan He
2020-06-24 2:14 ` Baoquan He
2020-06-24 3:46 ` Wei Yang
2020-06-24 3:52 ` Baoquan He
2020-06-24 3:56 ` Wei Yang
2020-06-24 8:51 ` David Hildenbrand
2020-06-24 22:08 ` Wei Yang
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