Messages in this thread | | | Date | Wed, 18 Dec 2013 10:11:43 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs |
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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@linux.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@oracle.com> > Signed-off-by: Wanpeng Li <liwanp@linux.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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