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Message-ID: <52B166CF.6080300@suse.cz>
Date: Wed, 18 Dec 2013 10:11:43 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
Sasha Levin <sasha.levin@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Michel Lespinasse <walken@...gle.com>,
Bob Liu <bob.liu@...cle.com>, npiggin@...e.de,
kosaki.motohiro@...fujitsu.com, riel@...hat.com,
David Rientjes <rientjes@...gle.com>,
Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
Hugh Dickins <hughd@...gle.com>,
Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs
On 12/18/2013 05:12 AM, Wanpeng Li wrote:
> Hi Sasha,
> On Tue, Dec 17, 2013 at 10:32:53PM -0500, Sasha Levin wrote:
>> On 12/17/2013 10:23 PM, Wanpeng Li wrote:
>>> - mlock_vma_page(page); /* no-op if already mlocked */
>>> - if (page == check_page)
>>> + if (page != check_page && trylock_page(page)) {
>>> + mlock_vma_page(page); /* no-op if already mlocked */
>>> + unlock_page(page);
>>> + } else if (page == check_page) {
>>> + mlock_vma_page(page); /* no-op if already mlocked */
>>> ret = SWAP_MLOCK;
>>> + }
>>
>> Previously, if page != check_page and the page was locked, we'd call mlock_vma_page()
>> anyways. With this change, we don't. In fact, we'll just skip that entire block not doing
>> anything.
>
> Thanks for pointing out. ;-)
>
>>
>> If that's something that's never supposed to happen, can we add a
>>
>> VM_BUG_ON(page != check_page && PageLocked(page))
>>
>> Just to cover this new code path?
>>
>
> How about this one?
>
>
> 0001-3.patch
>
>
> From eab57d94c82fb3ab74b607a3ede0f5ce765ff2cc Mon Sep 17 00:00:00 2001
> From: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> Date: Wed, 18 Dec 2013 12:05:59 +0800
> Subject: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs
>
> objrmap doesn't work for nonlinear VMAs because the assumption that offset-into-file
> correlates with offset-into-virtual-addresses does not hold. Hence what
> try_to_unmap_cluster does is a mini "virtual scan" of each nonlinear VMA which maps
> the file to which the target page belongs. If vma locked, mlock the pages in the
> cluster, rather than unmapping them. However, not all pages are guarantee page
> locked instead of the check page. This patch fix the BUG by try to lock !check page
> if them are unlocked.
>
> [ 253.869145] kernel BUG at mm/mlock.c:82!
> [ 253.869549] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> [ 253.870098] Dumping ftrace buffer:
> [ 253.870098] (ftrace buffer empty)
> [ 253.870098] Modules linked in:
> [ 253.870098] CPU: 10 PID: 9162 Comm: trinity-child75 Tainted: G W 3.13.0-rc4-next-20131216-sasha-00011-g5f105ec-dirty #4137
> [ 253.873310] task: ffff8800c98cb000 ti: ffff8804d34e8000 task.ti: ffff8804d34e8000
> [ 253.873310] RIP: 0010:[<ffffffff81281f28>] [<ffffffff81281f28>] mlock_vma_page+0x18/0xc0
> [ 253.873310] RSP: 0000:ffff8804d34e99e8 EFLAGS: 00010246
> [ 253.873310] RAX: 006fffff8038002c RBX: ffffea00474944c0 RCX: ffff880807636000
> [ 253.873310] RDX: ffffea0000000000 RSI: 00007f17a9bca000 RDI: ffffea00474944c0
> [ 253.873310] RBP: ffff8804d34e99f8 R08: ffff880807020000 R09: 0000000000000000
> [ 253.873310] R10: 0000000000000001 R11: 0000000000002000 R12: 00007f17a9bca000
> [ 253.873310] R13: ffffea00474944c0 R14: 00007f17a9be0000 R15: ffff880807020000
> [ 253.873310] FS: 00007f17aa31a700(0000) GS:ffff8801c9c00000(0000) knlGS:0000000000000000
> [ 253.873310] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 253.873310] CR2: 00007f17a94fa000 CR3: 00000004d3b02000 CR4: 00000000000006e0
> [ 253.873310] DR0: 00007f17a74ca000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 253.873310] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> [ 253.873310] Stack:
> [ 253.873310] 0000000b3de28067 ffff880b3de28e50 ffff8804d34e9aa8 ffffffff8128bc31
> [ 253.873310] 0000000000000301 ffffea0011850220 ffff8809a4039000 ffffea0011850238
> [ 253.873310] ffff8804d34e9aa8 ffff880807636060 0000000000000001 ffff880807636348
> [ 253.873310] Call Trace:
> [ 253.873310] [<ffffffff8128bc31>] try_to_unmap_cluster+0x1c1/0x340
> [ 253.873310] [<ffffffff8128c60a>] try_to_unmap_file+0x20a/0x2e0
> [ 253.873310] [<ffffffff8128c7b3>] try_to_unmap+0x73/0x90
> [ 253.873310] [<ffffffff812b526d>] __unmap_and_move+0x18d/0x250
> [ 253.873310] [<ffffffff812b53e9>] unmap_and_move+0xb9/0x180
> [ 253.873310] [<ffffffff812b559b>] migrate_pages+0xeb/0x2f0
> [ 253.873310] [<ffffffff812a0660>] ? queue_pages_pte_range+0x1a0/0x1a0
> [ 253.873310] [<ffffffff812a193c>] migrate_to_node+0x9c/0xc0
> [ 253.873310] [<ffffffff812a30b8>] do_migrate_pages+0x1b8/0x240
> [ 253.873310] [<ffffffff812a3456>] SYSC_migrate_pages+0x316/0x380
> [ 253.873310] [<ffffffff812a31ec>] ? SYSC_migrate_pages+0xac/0x380
> [ 253.873310] [<ffffffff811763c6>] ? vtime_account_user+0x96/0xb0
> [ 253.873310] [<ffffffff812a34ce>] SyS_migrate_pages+0xe/0x10
> [ 253.873310] [<ffffffff843c4990>] tracesys+0xdd/0xe2
> [ 253.873310] Code: 0f 1f 00 65 48 ff 04 25 10 25 1d 00 48 83 c4 08
> 5b c9 c3 55 48 89 e5 53 48 83 ec 08 66 66 66 66 90 48 8b 07 48 89 fb
> a8 01 75 10 <0f> 0b 66 0f 1f 44 00 00 eb fe 66 0f 1f 44 00 00 f0 0f ba
> 2f 15
> [ 253.873310] RIP [<ffffffff81281f28>] mlock_vma_page+0x18/0xc0
> [ 253.873310] RSP <ffff8804d34e99e8>
> [ 253.904194] ---[ end trace be59c4a7f8edab3f ]---
>
> Reported-by: Sasha Levin <sasha.levin@...cle.com>
> Signed-off-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> ---
> mm/rmap.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 55c8b8d..1e24813 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1347,6 +1347,7 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
> unsigned long end;
> int ret = SWAP_AGAIN;
> int locked_vma = 0;
> + int we_locked = 0;
>
> address = (vma->vm_start + cursor) & CLUSTER_MASK;
> end = address + CLUSTER_SIZE;
> @@ -1385,9 +1386,15 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
> BUG_ON(!page || PageAnon(page));
>
> if (locked_vma) {
> - mlock_vma_page(page); /* no-op if already mlocked */
> - if (page == check_page)
> + if (page != check_page) {
> + we_locked = trylock_page(page);
If it's not us who has the page already locked, but somebody else, he
might unlock it at this point and then the BUG_ON in mlock_vma_page()
will trigger again.
> + mlock_vma_page(page); /* no-op if already mlocked */
> + if (we_locked)
> + unlock_page(page);
> + } else if (page == check_page) {
> + mlock_vma_page(page); /* no-op if already mlocked */
> ret = SWAP_MLOCK;
> + }
> continue; /* don't unmap */
> }
>
>
--
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