Re: Page migration issue with UBIFS

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi,

On Tue, 15 Mar 2016 15:16:11 +0100
Richard Weinberger <richard@nod.at> wrote:

> Hi!
> 
> We're facing this issue from 2014 on UBIFS:
> http://www.spinics.net/lists/linux-fsdevel/msg79941.html

Just to let you know I was able to reproduce the exact same bug on a
sama5d3 with UBIFS + CMA enabled (CMA allocation through the
generic DRM/CMA code), so I think we can exclude a platform specific
bug.

> 
> So sum up:
> UBIFS does not allow pages directly marked as dirty. It want's everyone to do it via UBIFS's
> ->wirte_end() and ->page_mkwirte() functions.
> This assumption *seems* to be violated by CMA which migrates pages.
> UBIFS enforces this because it has to account free space on the flash,
> in UBIFS speak "budget", for details please see fs/ubifs/file.c.
> 
> As in the report from 2014 the page is writable but not dirty.
> The kernel has this debug patch applied:
> http://www.spinics.net/lists/linux-fsdevel/msg80471.html
> But our kernel is based on v4.4 and does *not* use proprietary modules.
> 
> [  213.450000] page:debe03c0 count:3 mapcount:1 mapping:dce4b5fc index:0x2f
> [  213.460000] flags: 0x9(locked|uptodate)
> [  213.460000] page dumped because: try_to_unmap_one
> [  213.470000] pte_write: 1
> [  213.480000] UBIFS assert failed in ubifs_set_page_dirty at 1451 (pid 436)
> [  213.490000] CPU: 0 PID: 436 Comm: drm-stress-test Not tainted 4.4.4-00176-geaa802524636-dirty #1008
> [  213.490000] Hardware name: Allwinner sun4i/sun5i Families
> [  213.490000] [<c0015e70>] (unwind_backtrace) from [<c0012cdc>] (show_stack+0x10/0x14)
> [  213.490000] [<c0012cdc>] (show_stack) from [<c02ad834>] (dump_stack+0x8c/0xa0)
> [  213.490000] [<c02ad834>] (dump_stack) from [<c0236ee8>] (ubifs_set_page_dirty+0x44/0x50)
> [  213.490000] [<c0236ee8>] (ubifs_set_page_dirty) from [<c00fa0bc>] (try_to_unmap_one+0x10c/0x3a8)
> [  213.490000] [<c00fa0bc>] (try_to_unmap_one) from [<c00fadb4>] (rmap_walk+0xb4/0x290)
> [  213.490000] [<c00fadb4>] (rmap_walk) from [<c00fb1bc>] (try_to_unmap+0x64/0x80)
> [  213.490000] [<c00fb1bc>] (try_to_unmap) from [<c010dc28>] (migrate_pages+0x328/0x7a0)
> [  213.490000] [<c010dc28>] (migrate_pages) from [<c00d0cb0>] (alloc_contig_range+0x168/0x2f4)
> [  213.490000] [<c00d0cb0>] (alloc_contig_range) from [<c010ec00>] (cma_alloc+0x170/0x2c0)
> [  213.490000] [<c010ec00>] (cma_alloc) from [<c001a958>] (__alloc_from_contiguous+0x38/0xd8)
> [  213.490000] [<c001a958>] (__alloc_from_contiguous) from [<c001ad44>] (__dma_alloc+0x23c/0x274)
> [  213.490000] [<c001ad44>] (__dma_alloc) from [<c001ae08>] (arm_dma_alloc+0x54/0x5c)
> [  213.490000] [<c001ae08>] (arm_dma_alloc) from [<c035cecc>] (drm_gem_cma_create+0xb8/0xf0)
> [  213.490000] [<c035cecc>] (drm_gem_cma_create) from [<c035cf20>] (drm_gem_cma_create_with_handle+0x1c/0xe8)
> [  213.490000] [<c035cf20>] (drm_gem_cma_create_with_handle) from [<c035d088>] (drm_gem_cma_dumb_create+0x3c/0x48)
> [  213.490000] [<c035d088>] (drm_gem_cma_dumb_create) from [<c0341ed8>] (drm_ioctl+0x12c/0x444)
> [  213.490000] [<c0341ed8>] (drm_ioctl) from [<c0121adc>] (do_vfs_ioctl+0x3f4/0x614)
> [  213.490000] [<c0121adc>] (do_vfs_ioctl) from [<c0121d30>] (SyS_ioctl+0x34/0x5c)
> [  213.490000] [<c0121d30>] (SyS_ioctl) from [<c000f2c0>] (ret_fast_syscall+0x0/0x34)
> 
> The full kernellog can be found here:
> http://code.bulix.org/ysuo9x-93716?raw
> 
> So, let me repeat Artem's question from 2014:
> > Now the question is: is it UBIFS which has incorrect assumptions, or this is the
> > Linux MM which is not doing the right thing? I do not know the answer, let's see
> > if the MM list may give us a clue.
> 
> Thanks,
> //richard



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com