Re: kernel oops on mmotm-2015-10-15-15-20

[Minchan Kim <minchan@kernel.org>]

On Thu, Oct 29, 2015 at 02:25:24AM +0200, Kirill A. Shutemov wrote:
> On Thu, Oct 22, 2015 at 06:00:51PM +0900, Minchan Kim wrote:
> > On Thu, Oct 22, 2015 at 10:21:36AM +0900, Minchan Kim wrote:
> > > Hello Hugh,
> > > 
> > > On Wed, Oct 21, 2015 at 05:59:59PM -0700, Hugh Dickins wrote:
> > > > On Thu, 22 Oct 2015, Minchan Kim wrote:
> > > > > 
> > > > > I added the code to check it and queued it again but I had another oops
> > > > > in this time but symptom is related to anon_vma, too.
> > > > > (kernel is based on recent mmotm + unconditional mkdirty for bug fix)
> > > > > It seems page_get_anon_vma returns NULL since the page was not page_mapped
> > > > > at that time but second check of page_mapped right before try_to_unmap seems
> > > > > to be true.
> > > > > 
> > > > > Adding 4191228k swap on /dev/vda5.  Priority:-1 extents:1 across:4191228k FS
> > > > > Adding 4191228k swap on /dev/vda5.  Priority:-1 extents:1 across:4191228k FS
> > > > > page:ffffea0001cfbfc0 count:3 mapcount:1 mapping:ffff88007f1b5f51 index:0x600000aff
> > > > > flags: 0x4000000000048019(locked|uptodate|dirty|swapcache|swapbacked)
> > > > > page dumped because: VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma)
> > > > 
> > > > That's interesting, that's one I added in my page migration series.
> > > > Let me think on it, but it could well relate to the one you got before.
> > > 
> > > I will roll back to mm/madv_free-v4.3-rc5-mmotm-2015-10-15-15-20
> > > instead of next-20151021 to remove noise from your migration cleanup
> > > series and will test it again.
> > > If it is fixed, I will test again with your migration patchset, then.
> > 
> > I tested mmotm-2015-10-15-15-20 with test program I attach for a long time.
> > Therefore, there is no patchset from Hugh's migration patch in there.
> > And I added below debug code with request from Kirill to all test kernels.
> 
> It took too long time (and a lot of printk()), but I think I track it down
> finally.
>  
> The patch below seems fixes issue for me. It's not yet properly tested, but
> looks like it works.
> 
> The problem was my wrong assumption on how migration works: I thought that
> kernel would wait migration to finish on before deconstruction mapping.
> 
> But turn out that's not true.
> 
> As result if zap_pte_range() races with split_huge_page(), we can end up
> with page which is not mapped anymore but has _count and _mapcount
> elevated. The page is on LRU too. So it's still reachable by vmscan and by
> pfn scanners (Sasha showed few similar traces from compaction too).
> It's likely that page->mapping in this case would point to freed anon_vma.
> 
> BOOM!
> 
> The patch modify freeze/unfreeze_page() code to match normal migration
> entries logic: on setup we remove page from rmap and drop pin, on removing
> we get pin back and put page on rmap. This way even if migration entry
> will be removed under us we don't corrupt page's state.
> 
> Please, test.
> 

kernel: On mmotm-2015-10-15-15-20 + pte_mkdirty patch + your new patch, I tested
one I sent to you(ie, oops.c + memcg_test.sh)

page:ffffea00016a0000 count:3 mapcount:0 mapping:ffff88007f49d001 index:0x600001800 compound_mapcount: 0
flags: 0x4000000000044009(locked|uptodate|head|swapbacked)
page dumped because: VM_BUG_ON_PAGE(!page_mapcount(page))
page->mem_cgroup:ffff88007f613c00
------------[ cut here ]------------
kernel BUG at mm/rmap.c:1156!
invalid opcode: 0000 [#1] SMP 
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 7 PID: 3312 Comm: oops Not tainted 4.3.0-rc5-mm1-madv-free-no-lazy-thp+ #1573
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff8800b8804ec0 ti: ffff88000005c000 task.ti: ffff88000005c000
RIP: 0010:[<ffffffff81128223>]  [<ffffffff81128223>] do_page_add_anon_rmap+0x323/0x360
RSP: 0000:ffff88000005f758  EFLAGS: 00010292
RAX: 0000000000000021 RBX: ffffea00016a0000 RCX: ffffffff81830db8
RDX: 0000000000000001 RSI: 0000000000000246 RDI: ffffffff821df4d8
RBP: ffff88000005f780 R08: 0000000000000000 R09: ffff8800000b8be0
R10: ffffffff8163d7c0 R11: 00000000000001a5 R12: ffff88007e85ddc0
R13: 0000600001800000 R14: 0000000000000000 R15: ffff88007e85ddc0
FS:  00007f5cd5fea740(0000) GS:ffff8800bfae0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000600004c03000 CR3: 000000007f017000 CR4: 00000000000006a0
Stack:
 ffff88007f351000 ffff88007f352000 ffffea00016a0000 0000600001800000
 ffff88007e85ddc0 ffff88000005f790 ffffffff81128278 ffff88000005f800
 ffffffff81146dbb 00000006000019ff 0000000600001800 0000160000000000
Call Trace:
 [<ffffffff81128278>] page_add_anon_rmap+0x18/0x20
 [<ffffffff81146dbb>] unfreeze_page+0x24b/0x330
 [<ffffffff8114bb5f>] split_huge_page_to_list+0x3df/0x920
 [<ffffffff811321cf>] ? scan_swap_map+0x37f/0x550
 [<ffffffff8112f996>] add_to_swap+0xb6/0x100
 [<ffffffff81103c87>] shrink_page_list+0x3b7/0xdc0
 [<ffffffff81104d4c>] shrink_inactive_list+0x18c/0x4b0
 [<ffffffff811059af>] shrink_lruvec+0x58f/0x730
 [<ffffffff81105c24>] shrink_zone+0xd4/0x280
 [<ffffffff81105efd>] do_try_to_free_pages+0x12d/0x3b0
 [<ffffffff8110635d>] try_to_free_mem_cgroup_pages+0x9d/0x120
 [<ffffffff8114e2f5>] try_charge+0x175/0x720
 [<ffffffff812728c3>] ? radix_tree_lookup_slot+0x13/0x30
 [<ffffffff810efd6e>] ? find_get_entry+0x1e/0xc0
 [<ffffffff811520c5>] mem_cgroup_try_charge+0x85/0x1d0
 [<ffffffff8111c4d7>] do_swap_page+0xd7/0x5a0
 [<ffffffff8111e203>] handle_mm_fault+0x803/0x1000
 [<ffffffff8106efda>] ? pick_next_task_fair+0x3ba/0x480
 [<ffffffff8105f8c0>] ? finish_task_switch+0x70/0x260
 [<ffffffff81033629>] __do_page_fault+0x189/0x400
 [<ffffffff810338ac>] do_page_fault+0xc/0x10
 [<ffffffff81428842>] page_fault+0x22/0x30




> Not-Yet-Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 5e0fe82a0fae..192b50c7526c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2934,6 +2934,13 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>  
>  	smp_wmb(); /* make pte visible before pmd */
>  	pmd_populate(mm, pmd, pgtable);
> +
> +	if (freeze) {
> +		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> +			page_remove_rmap(page + i, false);
> +			put_page(page + i);
> +		}
> +	}
>  }
>  
>  void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> @@ -3079,6 +3086,8 @@ static void freeze_page_vma(struct vm_area_struct *vma, struct page *page,
>  		if (pte_soft_dirty(entry))
>  			swp_pte = pte_swp_mksoft_dirty(swp_pte);
>  		set_pte_at(vma->vm_mm, address, pte + i, swp_pte);
> +		page_remove_rmap(page, false);
> +		put_page(page);
>  	}
>  	pte_unmap_unlock(pte, ptl);
>  }
> @@ -3117,8 +3126,6 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
>  		return;
>  	pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
>  	for (i = 0; i < HPAGE_PMD_NR; i++, address += PAGE_SIZE, page++) {
> -		if (!page_mapped(page))
> -			continue;
>  		if (!is_swap_pte(pte[i]))
>  			continue;
>  
> @@ -3128,6 +3135,9 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
>  		if (migration_entry_to_page(swp_entry) != page)
>  			continue;
>  
> +		get_page(page);
> +		page_add_anon_rmap(page, vma, address, false);
> +
>  		entry = pte_mkold(mk_pte(page, vma->vm_page_prot));
>  		entry = pte_mkdirty(entry);
>  		if (is_write_migration_entry(swp_entry))
> -- 
>  Kirill A. Shutemov
> 
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