linux-kernel - Re: [PATCH v2 1/3] mm: memory-failure: update ttu flag inside unmap_poisoned

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Message-ID: <52d2b3ed-6a4b-4c44-a56f-56840ecd971c@redhat.com>
Date: Mon, 20 Jan 2025 08:55:31 +0100
From: David Hildenbrand <david@...hat.com>
To: Wupeng Ma <mawupeng1@...wei.com>, akpm@...ux-foundation.org,
 osalvador@...e.de, nao.horiguchi@...il.com, linmiaohe@...wei.com,
 mhocko@...e.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] mm: memory-failure: update ttu flag inside
 unmap_poisoned_folio

On 16.01.25 07:16, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> Commit 6da6b1d4a7df ("mm/hwpoison: convert TTU_IGNORE_HWPOISON to
> TTU_HWPOISON") introduce TTU_HWPOISON to replace TTU_IGNORE_HWPOISON
> in order to stop send SIGBUS signal when accessing an error page after
> a memory error on a clean folio. However during page migration, anon
> folio must be set with TTU_HWPOISON during unmap_*(). For pagecache
> we need some policy just like the one in hwpoison_user_mappings to
> set this flag. So move this policy from hwpoison_user_mappings to
> unmap_poisoned_folio to handle this waring properly.
> 
> Waring will be produced during unamp poison folio with the following log:
> 
>    ------------[ cut here ]------------
>    WARNING: CPU: 1 PID: 365 at mm/rmap.c:1847 try_to_unmap_one+0x8fc/0xd3c
>    Modules linked in:
>    CPU: 1 UID: 0 PID: 365 Comm: bash Tainted: G        W          6.13.0-rc1-00018-gacdb4bbda7ab #42
>    Tainted: [W]=WARN
>    Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
>    pstate: 20400005 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>    pc : try_to_unmap_one+0x8fc/0xd3c
>    lr : try_to_unmap_one+0x3dc/0xd3c
>    Call trace:
>     try_to_unmap_one+0x8fc/0xd3c (P)
>     try_to_unmap_one+0x3dc/0xd3c (L)
>     rmap_walk_anon+0xdc/0x1f8
>     rmap_walk+0x3c/0x58
>     try_to_unmap+0x88/0x90
>     unmap_poisoned_folio+0x30/0xa8
>     do_migrate_range+0x4a0/0x568
>     offline_pages+0x5a4/0x670
>     memory_block_action+0x17c/0x374
>     memory_subsys_offline+0x3c/0x78
>     device_offline+0xa4/0xd0
>     state_store+0x8c/0xf0
>     dev_attr_store+0x18/0x2c
>     sysfs_kf_write+0x44/0x54
>     kernfs_fop_write_iter+0x118/0x1a8
>     vfs_write+0x3a8/0x4bc
>     ksys_write+0x6c/0xf8
>     __arm64_sys_write+0x1c/0x28
>     invoke_syscall+0x44/0x100
>     el0_svc_common.constprop.0+0x40/0xe0
>     do_el0_svc+0x1c/0x28
>     el0_svc+0x30/0xd0
>     el0t_64_sync_handler+0xc8/0xcc
>     el0t_64_sync+0x198/0x19c
>    ---[ end trace 0000000000000000 ]---
> 
> Fixes: 6da6b1d4a7df ("mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU_HWPOISON")
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> Suggested-by: David Hildenbrand <david@...hat.com>

Your SOB should probably come last.

With or without moving folio_mapped() into unmap_poisoned_folio():

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb