Re: [PATCH] mm/hugetlb: fix kernel NULL pointer dereference when migrating hugetlb folio

[Miaohe Lin]

On 2024/7/9 19:58, Miaohe Lin wrote:
> A kernel crash was observed when migrating hugetlb folio:
> 
> BUG: kernel NULL pointer dereference, address: 0000000000000008
> PGD 0 P4D 0
> Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI
> CPU: 0 PID: 3435 Comm: bash Not tainted 6.10.0-rc6-00450-g8578ca01f21f #66
> RIP: 0010:__folio_undo_large_rmappable+0x70/0xb0
> RSP: 0018:ffffb165c98a7b38 EFLAGS: 00000097
> RAX: fffffbbc44528090 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffffa30e000a2800 RSI: 0000000000000246 RDI: ffffa3153ffffcc0
> RBP: fffffbbc44528000 R08: 0000000000002371 R09: ffffffffbe4e5868
> R10: 0000000000000001 R11: 0000000000000001 R12: ffffa3153ffffcc0
> R13: fffffbbc44468000 R14: 0000000000000001 R15: 0000000000000001
> FS:  00007f5b3a716740(0000) GS:ffffa3151fc00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000008 CR3: 000000010959a000 CR4: 00000000000006f0
> Call Trace:
>  <TASK>
>  __folio_migrate_mapping+0x59e/0x950
>  __migrate_folio.constprop.0+0x5f/0x120
>  move_to_new_folio+0xfd/0x250
>  migrate_pages+0x383/0xd70
>  soft_offline_page+0x2ab/0x7f0
>  soft_offline_page_store+0x52/0x90
>  kernfs_fop_write_iter+0x12c/0x1d0
>  vfs_write+0x380/0x540
>  ksys_write+0x64/0xe0
>  do_syscall_64+0xb9/0x1d0
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f5b3a514887
> RSP: 002b:00007ffe138fce68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 000000000000000c RCX: 00007f5b3a514887
> RDX: 000000000000000c RSI: 0000556ab809ee10 RDI: 0000000000000001
> RBP: 0000556ab809ee10 R08: 00007f5b3a5d1460 R09: 000000007fffffff
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c
> R13: 00007f5b3a61b780 R14: 00007f5b3a617600 R15: 00007f5b3a616a00
> 
> It's because hugetlb folio is passed to __folio_undo_large_rmappable()
> unexpectedly. large_rmappable flag is imperceptibly set to hugetlb folio
> since commit f6a8dd98a2ce ("hugetlb: convert alloc_buddy_hugetlb_folio to
> use a folio"). Then commit be9581ea8c05 ("mm: fix crashes from deferred
> split racing folio migration") makes folio_migrate_mapping() call
> folio_undo_large_rmappable() triggering the bug. Fix this issue by
> clearing large_rmappable flag for hugetlb folios. They don't need that
> flag set anyway.
> 
> Fixes: f6a8dd98a2ce ("hugetlb: convert alloc_buddy_hugetlb_folio to use a folio")
> Fixes: be9581ea8c05 ("mm: fix crashes from deferred split racing folio migration")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>

Sorry for make noise. This is not newest version. Will resend soon.
Thanks.
.