Page migration issue with UBIFS

[Richard Weinberger]

Adding more CC's.

Am 16.03.2016 um 15:27 schrieb Kirill A. Shutemov:
> On Wed, Mar 16, 2016 at 05:21:56PM +0300, Kirill A. Shutemov wrote:
>> On Wed, Mar 16, 2016 at 12:18:50AM +0100, Richard Weinberger wrote:
>>> Am 15.03.2016 um 16:37 schrieb Christoph Hellwig:
>>>> On Tue, Mar 15, 2016 at 04:32:40PM +0100, Richard Weinberger wrote:
>>>>>> Or if ->page_mkwrite() was called, why the page is not dirty?
>>>>>
>>>>> BTW: UBIFS does not implement ->migratepage(), could this be a problem?
>>>>
>>>> This might be the reason.  I can't reall make sense of
>>>> buffer_migrate_page, but it seems to migrate buffer_head state to
>>>> the new page.
>>>>
>>>> I'd love to know why CMA even tries to migrate pages that don't have a
>>>> ->migratepage method, this seems incredibly dangerous to me.
>>>
>>> FYI, with a dummy ->migratepage() which returns only -EINVAL UBIFS does no
>>> longer explode upon page migration.
>>> Tomorrow I'll do more tests to make sure.
>>
>> Could you check if something like this would fix the issue.

Nope.

[  108.080000] BUG: Bad page state in process drm-stress-test  pfn:5c674
[  108.080000] page:deb8ce80 count:0 mapcount:0 mapping:  (null) index:0x0
[  108.090000] flags: 0x810(dirty|private)
[  108.100000] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
[  108.100000] bad because of flags:
[  108.110000] flags: 0x800(private)
[  108.110000] Modules linked in:
[  108.120000] CPU: 0 PID: 1855 Comm: drm-stress-test Not tainted 4.4.4-gaae1ad1-dirty #14
[  108.120000] Hardware name: Allwinner sun4i/sun5i Families
[  108.120000] [<c0015eb4>] (unwind_backtrace) from [<c0012cec>] (show_stack+0x10/0x14)
[  108.120000] [<c0012cec>] (show_stack) from [<c02abaf8>] (dump_stack+0x8c/0xa0)
[  108.120000] [<c02abaf8>] (dump_stack) from [<c00cbe78>] (bad_page+0xcc/0x11c)
[  108.120000] [<c00cbe78>] (bad_page) from [<c00cc0f4>] (free_pages_prepare+0x22c/0x2f4)
[  108.120000] [<c00cc0f4>] (free_pages_prepare) from [<c00cdf2c>] (free_hot_cold_page+0x34/0x194)
[  108.120000] [<c00cdf2c>] (free_hot_cold_page) from [<c00ce0d4>] (free_hot_cold_page_list+0x48/0xdc)
[  108.120000] [<c00ce0d4>] (free_hot_cold_page_list) from [<c00d55a8>] (release_pages+0x1dc/0x224)
[  108.120000] [<c00d55a8>] (release_pages) from [<c00d56d8>] (pagevec_lru_move_fn+0xe8/0xf8)
[  108.120000] [<c00d56d8>] (pagevec_lru_move_fn) from [<c00d579c>] (__lru_cache_add+0x60/0x88)
[  108.120000] [<c00d579c>] (__lru_cache_add) from [<c00d9578>] (putback_lru_page+0x68/0xbc)
[  108.120000] [<c00d9578>] (putback_lru_page) from [<c010bd6c>] (migrate_pages+0x208/0x730)
[  108.120000] [<c010bd6c>] (migrate_pages) from [<c00d0860>] (alloc_contig_range+0x168/0x2f4)
[  108.120000] [<c00d0860>] (alloc_contig_range) from [<c010cdb4>] (cma_alloc+0x170/0x2c0)
[  108.120000] [<c010cdb4>] (cma_alloc) from [<c001a9d4>] (__alloc_from_contiguous+0x38/0xd8)
[  108.120000] [<c001a9d4>] (__alloc_from_contiguous) from [<c001adb8>] (__dma_alloc+0x234/0x278)
[  108.120000] [<c001adb8>] (__dma_alloc) from [<c001ae8c>] (arm_dma_alloc+0x54/0x5c)
[  108.120000] [<c001ae8c>] (arm_dma_alloc) from [<c035bd70>] (drm_gem_cma_create+0x9c/0xf0)
[  108.120000] [<c035bd70>] (drm_gem_cma_create) from [<c035bde0>] (drm_gem_cma_create_with_handle+0x1c/0xe8)
[  108.120000] [<c035bde0>] (drm_gem_cma_create_with_handle) from [<c035bf48>] (drm_gem_cma_dumb_create+0x3c/0x48)
[  108.120000] [<c035bf48>] (drm_gem_cma_dumb_create) from [<c0340d18>] (drm_ioctl+0x12c/0x440)
[  108.120000] [<c0340d18>] (drm_ioctl) from [<c011fc7c>] (do_vfs_ioctl+0x3f4/0x614)
[  108.120000] [<c011fc7c>] (do_vfs_ioctl) from [<c011fed0>] (SyS_ioctl+0x34/0x5c)
[  108.120000] [<c011fed0>] (SyS_ioctl) from [<c000f2c0>] (ret_fast_syscall+0x0/0x34)

It is still not clear why UBIFS has to provide a >migratepage() and what the expected semantics
are.
What we know so far is that the fall back migration function is broken. I'm sure not only on UBIFS.

Can CMA folks please clarify? :-)

Thanks,
//richard