Re: [PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[Huacai Chen <chenhuacai@kernel.org>]

Hi, David,

On Sat, Aug 16, 2025 at 3:28 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 16.08.25 09:21, Huacai Chen wrote:
> > After commit 84caf98838a3e5f4bdb34 ("mm: stop storing migration_ops in
> > page->mapping") we get such an error message if CONFIG_ZSMALLOC=m:
> >
> >   WARNING: CPU: 3 PID: 42 at mm/migrate.c:142 isolate_movable_ops_page+0xa8/0x1c0
> >   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
> >   pc 9000000000540bd8 ra 9000000000540b84 tp 9000000100420000 sp 9000000100423a60
> >   a0 9000000100193a80 a1 000000000000000c a2 000000000000001b a3 ffffffffffffffff
> >   a4 ffffffffffffffff a5 0000000000000267 a6 0000000000000000 a7 9000000100423ae0
> >   t0 00000000000000f1 t1 00000000000000f6 t2 0000000000000000 t3 0000000000000001
> >   t4 ffffff00010eb834 t5 0000000000000040 t6 900000010c89d380 t7 90000000023fcc70
> >   t8 0000000000000018 u0 0000000000000000 s9 ffffff00010eb800 s0 ffffff00010eb800
> >   s1 000000000000000c s2 0000000000043ae0 s3 0000800000000000 s4 900000000219cc40
> >   s5 0000000000000000 s6 ffffff00010eb800 s7 0000000000000001 s8 90000000025b4000
> >      ra: 9000000000540b84 isolate_movable_ops_page+0x54/0x1c0
> >     ERA: 9000000000540bd8 isolate_movable_ops_page+0xa8/0x1c0
> >    CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> >    PRMD: 00000004 (PPLV0 +PIE -PWE)
> >    EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
> >    ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> >   ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
> >    PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
> >   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
> >   Stack : 90000000021fd000 0000000000000000 9000000000247720 9000000100420000
> >           90000001004236a0 90000001004236a8 0000000000000000 90000001004237e8
> >           90000001004237e0 90000001004237e0 9000000100423550 0000000000000001
> >           0000000000000001 90000001004236a8 725a84864a19e2d9 90000000023fcc58
> >           9000000100420000 90000000024c6848 9000000002416848 0000000000000001
> >           0000000000000000 000000000000000a 0000000007fe0000 ffffff00010eb800
> >           0000000000000000 90000000021fd000 0000000000000000 900000000205cf30
> >           000000000000008e 0000000000000009 ffffff00010eb800 0000000000000001
> >           90000000025b4000 0000000000000000 900000000024773c 00007ffff103d748
> >           00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d
> >           ...
> >   Call Trace:
> >   [<900000000024773c>] show_stack+0x5c/0x190
> >   [<90000000002415e0>] dump_stack_lvl+0x70/0x9c
> >   [<90000000004abe6c>] isolate_migratepages_block+0x3bc/0x16e0
> >   [<90000000004af408>] compact_zone+0x558/0x1000
> >   [<90000000004b0068>] compact_node+0xa8/0x1e0
> >   [<90000000004b0aa4>] kcompactd+0x394/0x410
> >   [<90000000002b3c98>] kthread+0x128/0x140
> >   [<9000000001779148>] ret_from_kernel_thread+0x28/0xc0
> >   [<9000000000245528>] ret_from_kernel_thread_asm+0x10/0x88
> >
> > The reason is that defined(CONFIG_ZSMALLOC) evaluates to 1 only when
> > CONFIG_ZSMALLOC=y, we should use IS_ENABLED(CONFIG_ZSMALLOC) instead.
> > But when I use IS_ENABLED(CONFIG_ZSMALLOC), page_movable_ops() cannot
> > access zsmalloc_mops because zsmalloc_mops is in a module.
> >
> > To solve this problem, we define a movable_ops[] array in mm/migrate.c,
> > initialise its elements at mm/balloon_compaction.c & mm/zsmalloc.c, and
> > let the page_movable_ops() function return elements from movable_ops[].
> >
> > Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping")
> > Acked-by: Zi Yan <ziy@nvidia.com>
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> > ---
> > V2: Use EXPORT_SYMBOL_GPL_FOR_MODULES instead of EXPORT_SYMBOL and fix build.
>
> See my review.
>
> Please wait longer for a resend, so we don't have to do this weird
> review dance.
I'm sorry, when I receive Zi Yan's Ack I think there is no big
problems, so I sent V2.

Huacai

>
> --
> Cheers
>
> David / dhildenb
>