Re: [PATCH] mm/mlock: fix BUG_ON unlocked page for nolinear VMAs

[Vlastimil Babka <vbabka@suse.cz>]

On 12/17/2013 09:05 AM, Wanpeng Li wrote:
> 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 just confirm check page
> hold page lock instead of all pages in the virtual scan window against nolinear VMAs.

This may fix the symptom, but I don't understand from the description 
why in this case is it ok not to have page locked for mlock_vma_page(), 
while in the other cases it's not ok.

> [  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/huge_memory.c | 2 +-
>   mm/internal.h    | 4 ++--
>   mm/ksm.c         | 2 +-
>   mm/memory.c      | 2 +-
>   mm/mlock.c       | 5 +++--
>   mm/rmap.c        | 4 ++--
>   6 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 33a5dc4..7a15b04 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1264,7 +1264,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>   		if (page->mapping && trylock_page(page)) {
>   			lru_add_drain();
>   			if (page->mapping)
> -				mlock_vma_page(page);
> +				mlock_vma_page(page, true);
>   			unlock_page(page);
>   		}
>   	}
> diff --git a/mm/internal.h b/mm/internal.h
> index a85a3ab..4ea2d4e 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -192,7 +192,7 @@ static inline int mlocked_vma_newpage(struct vm_area_struct *vma,
>   /*
>    * must be called with vma's mmap_sem held for read or write, and page locked.
>    */
> -extern void mlock_vma_page(struct page *page);
> +extern void mlock_vma_page(struct page *page, bool check_page);
>   extern unsigned int munlock_vma_page(struct page *page);
>
>   /*
> @@ -236,7 +236,7 @@ static inline int mlocked_vma_newpage(struct vm_area_struct *v, struct page *p)
>   	return 0;
>   }
>   static inline void clear_page_mlock(struct page *page) { }
> -static inline void mlock_vma_page(struct page *page) { }
> +static inline void mlock_vma_page(struct page *page, bool check_page) { }
>   static inline void mlock_migrate_page(struct page *new, struct page *old) { }
>
>   #endif /* !CONFIG_MMU */
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 175fff7..ec36f04 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -1064,7 +1064,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
>   		if (!PageMlocked(kpage)) {
>   			unlock_page(page);
>   			lock_page(kpage);
> -			mlock_vma_page(kpage);
> +			mlock_vma_page(kpage, true);
>   			page = kpage;		/* for final unlock */
>   		}
>   	}
> diff --git a/mm/memory.c b/mm/memory.c
> index cf6098c..a41df6a 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1602,7 +1602,7 @@ split_fallthrough:
>   			 * know the page is still mapped, we don't even
>   			 * need to check for file-cache page truncation.
>   			 */
> -			mlock_vma_page(page);
> +			mlock_vma_page(page, true);
>   			unlock_page(page);
>   		}
>   	}
> diff --git a/mm/mlock.c b/mm/mlock.c
> index d480cd6..c395ec5 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -77,9 +77,10 @@ void clear_page_mlock(struct page *page)
>    * Mark page as mlocked if not already.
>    * If page on LRU, isolate and putback to move to unevictable list.
>    */
> -void mlock_vma_page(struct page *page)
> +void mlock_vma_page(struct page *page, bool check_page)
>   {
> -	BUG_ON(!PageLocked(page));
> +	if (check_page)
> +		BUG_ON(!PageLocked(page));
>
>   	if (!TestSetPageMlocked(page)) {
>   		mod_zone_page_state(page_zone(page), NR_MLOCK,
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 55c8b8d..79d456f 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1297,7 +1297,7 @@ out_mlock:
>   	 */
>   	if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
>   		if (vma->vm_flags & VM_LOCKED) {
> -			mlock_vma_page(page);
> +			mlock_vma_page(page, true);
>   			ret = SWAP_MLOCK;
>   		}
>   		up_read(&vma->vm_mm->mmap_sem);
> @@ -1385,7 +1385,7 @@ 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 */
> +			mlock_vma_page(page, page == check_page);   /* no-op if already mlocked */
>   			if (page == check_page)
>   				ret = SWAP_MLOCK;
>   			continue;	/* don't unmap */
>

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