Re: Page migration issue with UBIFS

[Andrew Morton]

On Wed, 16 Mar 2016 21:47:20 +0100 Richard Weinberger <richard@xxxxxx> wrote:

> 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.
> 

The above says "PagePrivate was still set", and UBIFS does muck with
PagePrivate.  Perhaps the fs isn't clearing things up in all the right
places.