RE: [RFC PATCH] mm: move xa forward when run across zombie page

[Hugh Dickins <hughd@google.com>]

On Mon, 31 Oct 2022, Pulavarty, Badari wrote:

> Hi,
> 
> Just want to give an update on the issue, hoping to get more thoughts/suggestions.
> 
> I have been adding lot of debug to try to root cause the issue.
> When I enabled CONFIG_VM_DEBUG, I run into following assertion failure:
> 
> [ 1810.282055] entry: 0 folio: ffe6dfc30e428040 
> [ 1810.282059] page dumped because: VM_BUG_ON_PAGE(entry != folio)
> [ 1810.282062] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 1810.282084] #PF: supervisor read access in kernel mode
> [ 1810.282095] #PF: error_code(0x0000) - not-present page
> [ 1810.282104] PGD 0
> [ 1810.282110] Oops: 0000 [#1] PREEMPT SMP NOPTI
> [ 1810.282119] CPU: 86 PID: 15043 Comm: kdamond.1 Kdump: loaded Tainted: G S          E      6.1.0-rc1+ #32
> [ 1810.282145] RIP: 0010:dump_page+0x25/0x340
> [ 1810.282156] Code: 0b cc cc cc cc 0f 1f 44 00 00 55 48 89 e5 41 57 49 89 ff 41 56 41 55 49 89 f5 41 54 53 48 83 ec 20 48 85 f6 0f 85 7d 72 ab 00 <49> 8b 07 48 83 f8 ff 0f 84 82 71 ab 00 49 8b 5f 08 f6 c3 01 0f 85
> [ 1810.282185] RSP: 0018:ff3fae02170637b8 EFLAGS: 00010046
> [ 1810.282193] RAX: 0000000000000033 RBX: ffe6dfc30e428040 RCX: 0000000000000002
> [ 1810.282204] RDX: 0000000000000000 RSI: ffffffffb85ad649 RDI: 00000000ffffffff
> [ 1810.282215] RBP: ff3fae0217063800 R08: 0000000000000000 R09: c0000000fffeffff
> [ 1810.282225] R10: 0000000000000001 R11: ff3fae0217063620 R12: 0000000000000001
> [ 1810.282234] R13: ffffffffb85c87e0 R14: 0000000000000000 R15: 0000000000000000
> [ 1810.282244] FS:  0000000000000000(0000) GS:ff25c2ea7e780000(0000) knlGS:0000000000000000
> [ 1810.282255] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 1810.282264] CR2: 0000000000000000 CR3: 000000552f40a006 CR4: 0000000000771ee0
> [ 1810.282274] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 1810.282284] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
> [ 1810.282293] PKRU: 55555554
> [ 1810.282299] Call Trace:
> [ 1810.282304]  <TASK>
> [ 1810.282310]  __delete_from_swap_cache.cold.20+0x33/0x35
> [ 1810.282321]  delete_from_swap_cache+0x50/0xa0
> [ 1810.282330]  folio_free_swap+0xab/0xe0
> [ 1810.282339]  free_swap_cache+0x8a/0xa0
> [ 1810.282346]  free_page_and_swap_cache+0x12/0xb0
> [ 1810.282356]  split_huge_page_to_list+0xf13/0x10d0     <<<<<<<<<<<<<<<<<<
> [ 1810.282365]  madvise_cold_or_pageout_pte_range+0x528/0x1390
> [ 1810.282374]  walk_pgd_range+0x5fe/0xa10
> [ 1810.282383]  __walk_page_range+0x184/0x190
> [ 1810.282391]  walk_page_range+0x120/0x190
> [ 1810.282398]  madvise_pageout+0x10b/0x2a0
> [ 1810.282406]  ? set_track_prepare+0x48/0x70
> [ 1810.282415]  madvise_vma_behavior+0x2f2/0xb10
> [ 1810.282422]  ? find_vma_prev+0x72/0xc0
> [ 1810.282431]  do_madvise+0x21b/0x440
> [ 1810.282439]  damon_va_apply_scheme+0x76/0xa0
> [ 1810.282448]  kdamond_fn+0xbe9/0xe10
> [ 1810.282456]  ? damon_split_region_at+0x70/0x70
> [ 1810.282675]  kthread+0xfc/0x130
> [ 1810.282837]  ? kthread_complete_and_exit+0x20/0x20
> 
> Since I am not using hugepages explicitly..  I recompiled the kernel with 
> 
> CONFIG_TRANSPARENT_HUGEPAGE=n
> 
> And my problem went away (including the original issue).

For that one, please try with 6.1-rc3 (and CONFIG_TRANSPARENT_HUGEPAGE
back to y).  Mel put a fix to that kind of thing into 6.1-rc2, then I 
fixed its warning in 6.1-rc3 (git log -n2 mm/huge_memory.c tells more).

Hugh