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

[Kairui Song <ryncsn@gmail.com>]

On Sat, Aug 17, 2024 at 1:03 AM Usama Arif <usamaarif642@gmail.com> wrote:
> On 16/08/2024 17:55, Kairui Song wrote:
> > 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.
>
> Yes, this is also needed to prevent race with shrink_folio:
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index a6ca454e1168..75f5b059e804 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3183,6 +3183,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>
>                         folio_clear_active(new_folio);
>                         folio_clear_unevictable(new_folio);
> +                       list_del(&new_folio->lru);
>                         if (!folio_batch_add(&free_folios, new_folio)) {
>                                 mem_cgroup_uncharge_folios(&free_folios);
>                                 free_unref_folios(&free_folios);
>
>
> I have tested this so should be ok, but let me know otherwise.
>
> I will include this in the next revision I will send soon.
>
> Thanks.

Thanks for the update, the panic problem is gone.