Re: [PATCH v3 1/6] mm: free zapped tail pages when splitting isolated thp

Kairui Song
2024-08-16T16:56:01Z

On Fri, Aug 16, 2024 at 3:16 AM Usama Arif <usamaarif642@gmail.com> wrote:
> On 15/08/2024 19:47, Kairui Song wrote:
> > On Tue, Aug 13, 2024 at 8:03 PM Usama Arif <usamaarif642@gmail.com> wrote:
> >>
> >> From: Yu Zhao <yuzhao@google.com>
> >>
> >> If a tail page has only two references left, one inherited from the
> >> isolation of its head and the other from lru_add_page_tail() which we
> >> are about to drop, it means this tail page was concurrently zapped.
> >> Then we can safely free it and save page reclaim or migration the
> >> trouble of trying it.
> >>
> >> Signed-off-by: Yu Zhao <yuzhao@google.com>
> >> Tested-by: Shuang Zhai <zhais@google.com>
> >> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> >> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> >> ---
> >> mm/huge_memory.c | 27 +++++++++++++++++++++++++++
> >> 1 file changed, 27 insertions(+)
> >
> > Hi, Usama, Yu
> >
> > This commit is causing the kernel to panic very quickly with build
> > kernel test on top of tmpfs with all mTHP enabled, the panic comes
> > after:
> >
>
> Hi,
>
> Thanks for pointing this out. It is a very silly bug I have introduced going from v1 page version to the folio version of the patch in v3.
>
> Doing below over this patch will fix it:
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 907813102430..a6ca454e1168 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3183,7 +3183,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>
> folio_clear_active(new_folio);
> folio_clear_unevictable(new_folio);
> - if (!folio_batch_add(&free_folios, folio)) {
> + if (!folio_batch_add(&free_folios, new_folio)) {
> mem_cgroup_uncharge_folios(&free_folios);
> free_unref_folios(&free_folios);
> }
>
>
> I will include it in the next revision.
>

Hi,

After the fix, I'm still seeing below panic:
[ 24.926629] list_del corruption. prev->next should be
ffffea000491cf88, but was ffffea0006207708. (prev=ffffea000491cfc8)
[ 24.930783] ------------[ cut here ]------------
[ 24.932519] kernel BUG at lib/list_debug.c:64!
[ 24.934325] Oops: invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 24.936339] CPU: 32 UID: 0 PID: 2112 Comm: gzip Not tainted
6.11.0-rc3.ptch+ #147
[ 24.938575] Hardware name: Red Hat KVM/RHEL-AV, BIOS 0.0.0 02/06/2015
[ 24.940680] RIP: 0010:__list_del_entry_valid_or_report+0xaa/0xc0
[ 24.942536] Code: 8c ff 0f 0b 48 89 fe 48 c7 c7 f8 9d 51 82 e8 9d
36 8c ff 0f 0b 48 89 d1 48 89 f2 48 89 fe 48 c7 c7 30 9e 51 82 e8 86
36 8c ff <0f> 0b 48 c7 c7 80 9e 51 82 e8 78 36 8c ff 0f 0b 66 0f 1f 44
00 00
[ 24.948418] RSP: 0018:ffffc90005c2b770 EFLAGS: 00010246
[ 24.949996] RAX: 000000000000006d RBX: ffffea000491cf88 RCX: 0000000000000000
[ 24.952293] RDX: 0000000000000000 RSI: ffff889ffee1c180 RDI: ffff889ffee1c180
[ 24.954616] RBP: ffffea000491cf80 R08: 0000000000000000 R09: c0000000ffff7fff
[ 24.956908] R10: 0000000000000001 R11: ffffc90005c2b5a8 R12: ffffc90005c2b954
[ 24.959253] R13: ffffc90005c2bbc0 R14: ffffc90005c2b7c0 R15: ffffc90005c2b940
[ 24.961410] FS: 00007fe5a235e740(0000) GS:ffff889ffee00000(0000)
knlGS:0000000000000000
[ 24.963587] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 24.965112] CR2: 00007fe5a24ddcd0 CR3: 000000010cb40001 CR4: 0000000000770eb0
[ 24.967037] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 24.968933] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 24.970802] PKRU: 55555554
[ 24.971559] Call Trace:
[ 24.972241] <TASK>
[ 24.972805] ? __die_body+0x1e/0x60
[ 24.973756] ? die+0x3c/0x60
[ 24.974450] ? do_trap+0xe8/0x110
[ 24.975235] ? __list_del_entry_valid_or_report+0xaa/0xc0
[ 24.976543] ? do_error_trap+0x65/0x80
[ 24.977542] ? __list_del_entry_valid_or_report+0xaa/0xc0
[ 24.978891] ? exc_invalid_op+0x50/0x70
[ 24.979870] ? __list_del_entry_valid_or_report+0xaa/0xc0
[ 24.981295] ? asm_exc_invalid_op+0x1a/0x20
[ 24.982389] ? __list_del_entry_valid_or_report+0xaa/0xc0
[ 24.983781] shrink_folio_list+0x39a/0x1200
[ 24.984898] shrink_inactive_list+0x1c0/0x420
[ 24.986082] shrink_lruvec+0x5db/0x780
[ 24.987078] shrink_node+0x243/0xb00
[ 24.988063] ? get_pfnblock_flags_mask.constprop.117+0x1d/0x50
[ 24.989622] do_try_to_free_pages+0xbd/0x4e0
[ 24.990732] try_to_free_mem_cgroup_pages+0x107/0x230
[ 24.992034] try_charge_memcg+0x184/0x5d0
[ 24.993145] obj_cgroup_charge_pages+0x38/0x110
[ 24.994326] __memcg_kmem_charge_page+0x8d/0xf0
[ 24.995531] __alloc_pages_noprof+0x278/0x360
[ 24.996712] alloc_pages_mpol_noprof+0xf0/0x230
[ 24.997896] pipe_write+0x2ad/0x5f0
[ 24.998837] ? __pfx_tick_nohz_handler+0x10/0x10
[ 25.000234] ? update_process_times+0x8c/0xa0
[ 25.001377] ? timerqueue_add+0x77/0x90
[ 25.002257] vfs_write+0x39b/0x420
[ 25.003083] ksys_write+0xbd/0xd0
[ 25.003950] do_syscall_64+0x47/0x110
[ 25.004917] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 25.006210] RIP: 0033:0x7fe5a246f784
[ 25.007149] Code: c7 00 16 00 00 00 b8 ff ff ff ff c3 66 2e 0f 1f
84 00 00 00 00 00 f3 0f 1e fa 80 3d c5 08 0e 00 00 74 13 b8 01 00 00
00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 55 48 89 e5 48 83 ec 20
48 89
[ 25.011961] RSP: 002b:00007ffdb0057b38 EFLAGS: 00000202 ORIG_RAX:
0000000000000001
[ 25.013946] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fe5a246f784
[ 25.015817] RDX: 0000000000008000 RSI: 0000558c0d311420 RDI: 0000000000000001
[ 25.017717] RBP: 00007ffdb0057b60 R08: 0000558c0d258c40 R09: 0000558c0d311420
[ 25.019618] R10: 00007ffdb0057600 R11: 0000000000000202 R12: 0000000000008000
[ 25.021519] R13: 0000558c0d311420 R14: 0000000000000029 R15: 0000000000001f8d
[ 25.023412] </TASK>
[ 25.023998] Modules linked in:
[ 25.024900] ---[ end trace 0000000000000000 ]---
[ 25.026329] RIP: 0010:__list_del_entry_valid_or_report+0xaa/0xc0
[ 25.027885] Code: 8c ff 0f 0b 48 89 fe 48 c7 c7 f8 9d 51 82 e8 9d
36 8c ff 0f 0b 48 89 d1 48 89 f2 48 89 fe 48 c7 c7 30 9e 51 82 e8 86
36 8c ff <0f> 0b 48 c7 c7 80 9e 51 82 e8 78 36 8c ff 0f 0b 66 0f 1f 44
00 00
[ 25.032525] RSP: 0018:ffffc90005c2b770 EFLAGS: 00010246
[ 25.033892] RAX: 000000000000006d RBX: ffffea000491cf88 RCX: 0000000000000000
[ 25.035758] RDX: 0000000000000000 RSI: ffff889ffee1c180 RDI: ffff889ffee1c180
[ 25.037661] RBP: ffffea000491cf80 R08: 0000000000000000 R09: c0000000ffff7fff
[ 25.039543] R10: 0000000000000001 R11: ffffc90005c2b5a8 R12: ffffc90005c2b954
[ 25.041426] R13: ffffc90005c2bbc0 R14: ffffc90005c2b7c0 R15: ffffc90005c2b940
[ 25.043323] FS: 00007fe5a235e740(0000) GS:ffff889ffee00000(0000)
knlGS:0000000000000000
[ 25.045478] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 25.047013] CR2: 00007fe5a24ddcd0 CR3: 000000010cb40001 CR4: 0000000000770eb0
[ 25.048935] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 25.050858] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 25.052881] PKRU: 55555554
[ 25.053634] Kernel panic - not syncing: Fatal exception
[ 25.056902] Kernel Offset: disabled
[ 25.057827] ---[ end Kernel panic - not syncing: Fatal exception ]---

If I revert the fix and this patch, the panic is gone, let me know if
I can help debug it.