Re: [PATCH v3 0/3] page_owner: Fix refcount imbalance

[Kefeng Wang]

On 2024/3/26 14:30, Oscar Salvador wrote:
> This series consists of a refactoring/correctness of updating the metadata
> of tail pages and a couple of fixups for the refcounting part.
>
> > From this series on, instead of counting the stacks, we count the outstanding
> nr_base_pages each stack has, which gives us a much better memory overview.
> The other fixup is for the migration part.
>
> A more detailed explanation can be found in the changelog of the respective
> patches.

Hi Oscar, this patchset fix the following issue when I test my migration 
changes, but

[   31.478715] ------------[ cut here ]------------
[   31.480491] refcount_t: decrement hit 0; leaking memory.
[   31.482724] WARNING: CPU: 7 PID: 113 at lib/refcount.c:31 
refcount_warn_saturate+0x13c/0x148
[   31.485390] Modules linked in:
[   31.486800] CPU: 7 PID: 113 Comm: sh Not tainted 
6.9.0-rc1-00178-g317c7bc0ef03 #139
[   31.487883] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 
02/06/2015
[   31.489066] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS 
BTYPE=--)
[   31.489872] pc : refcount_warn_saturate+0x13c/0x148
[   31.490350] lr : refcount_warn_saturate+0x13c/0x148
[   31.490829] sp : ffff800087913650
[   31.491182] x29: ffff800087913650 x28: ffff00020624d010 x27: 
0000000000000000
[   31.492419] x26: 0000000000000001 x25: ffff800082dd0d60 x24: 
0000000000000000
[   31.493006] x23: 0000000754405c20 x22: ffff800082ec0000 x21: 
00000000028c008e
[   31.493527] x20: ffff0000d1638208 x19: ffff0000d1638200 x18: 
0000000000000010
[   31.493984] x17: 0000000000000006 x16: 0000000000000000 x15: 
ffff0000c6253c18
[   31.494330] x14: 0000000000000000 x13: 0000000000000002 x12: 
ffff800082dff318
[   31.494669] x11: ffff800082e6f640 x10: ffff800082e57600 x9 : 
ffff80008015869c
[   31.495056] x8 : 0000000000017fe8 x7 : c0000000ffffefff x6 : 
0000000000000001
[   31.495383] x5 : 0000000000057fa8 x4 : 0000000000000000 x3 : 
0000000000000000
[   31.495756] x2 : ffff800082dff228 x1 : 0000000000000000 x0 : 
0000000000000000
[   31.496367] Call trace:
[   31.496528]  refcount_warn_saturate+0x13c/0x148
[   31.496760]  __reset_page_owner+0x124/0x158
[   31.496965]  free_unref_page_prepare+0x2a4/0x440
[   31.497183]  free_unref_folios+0x118/0x460
[   31.497368]  folios_put_refs+0x11c/0x250
[   31.497559]  free_pages_and_swap_cache+0xd4/0x160
[   31.497772]  tlb_flush_mmu+0x8c/0x188
[   31.497952]  tlb_finish_mmu+0x54/0x160
[   31.498123]  exit_mmap+0x174/0x4e8
[   31.498295]  mmput+0xb4/0x1a0
[   31.498429]  begin_new_exec+0x474/0xd30
[   31.498606]  load_elf_binary+0x378/0x1488
[   31.498792]  bprm_execve+0x2a0/0x7e0
[   31.498956]  do_execveat_common.isra.0+0x19c/0x240
[   31.499174]  __arm64_sys_execve+0x48/0x68
[   31.499358]  invoke_syscall+0x4c/0x118
[   31.499534]  el0_svc_common.constprop.0+0x48/0xf0
[   31.499816]  do_el0_svc+0x24/0x38
[   31.500063]  el0_svc+0x4c/0x120
[   31.500314]  el0t_64_sync_handler+0xc0/0xc8
[   31.500584]  el0t_64_sync+0x190/0x198

I still see the following memory leak, could you check it?

/mnt/arm64 # cat /sys//kernel/debug/kmemleak
unreferenced object 0xffff000200d91000 (size 16):
  comm "kworker/4:0", pid 42, jiffies 4294892753
  hex dump (first 16 bytes):
    60 37 57 c1 00 00 ff ff 00 00 00 00 00 00 00 00  `7W.............
  backtrace (crc 4458f477):
    [<(____ptrval____)>] kmemleak_alloc+0x3c/0x50
    [<(____ptrval____)>] kmalloc_trace+0x20c/0x2e0
    [<(____ptrval____)>] __set_page_owner+0x1d0/0x2a0
    [<(____ptrval____)>] prep_new_page+0x108/0x138
    [<(____ptrval____)>] get_page_from_freelist+0x79c/0x16b8
    [<(____ptrval____)>] __alloc_pages+0x1bc/0x440
    [<(____ptrval____)>] new_slab+0x104/0x3c8
    [<(____ptrval____)>] ___slab_alloc+0x368/0xb20
    [<(____ptrval____)>] __slab_alloc.isra.0+0x3c/0x88
    [<(____ptrval____)>] kmalloc_trace+0x280/0x2e0
    [<(____ptrval____)>] __set_page_owner+0x1d0/0x2a0
    [<(____ptrval____)>] prep_new_page+0x108/0x138
    [<(____ptrval____)>] get_page_from_freelist+0x79c/0x16b8
    [<(____ptrval____)>] __alloc_pages+0x1bc/0x440
    [<(____ptrval____)>] new_slab+0x104/0x3c8
    [<(____ptrval____)>] ___slab_alloc+0x368/0xb20
unreferenced object 0xffff000200d90000 (size 16):
  comm "kworker/4:0", pid 42, jiffies 4294892753
  hex dump (first 16 bytes):
    20 38 57 c1 00 00 ff ff 00 10 d9 00 02 00 ff ff   8W.............
  backtrace (crc 786eca4d):
    [<(____ptrval____)>] kmemleak_alloc+0x3c/0x50
    [<(____ptrval____)>] kmalloc_trace+0x20c/0x2e0
    [<(____ptrval____)>] __set_page_owner+0x1d0/0x2a0
    [<(____ptrval____)>] prep_new_page+0x108/0x138
    [<(____ptrval____)>] get_page_from_freelist+0x79c/0x16b8
    [<(____ptrval____)>] __alloc_pages+0x1bc/0x440
    [<(____ptrval____)>] new_slab+0x104/0x3c8
    [<(____ptrval____)>] ___slab_alloc+0x368/0xb20
    [<(____ptrval____)>] __slab_alloc.isra.0+0x3c/0x88
    [<(____ptrval____)>] kmalloc_node_trace+0x274/0x2f0
    [<(____ptrval____)>] alloc_worker+0x2c/0x70
    [<(____ptrval____)>] create_worker+0x58/0x278
    [<(____ptrval____)>] worker_thread+0x260/0x320
    [<(____ptrval____)>] kthread+0x130/0x148
    [<(____ptrval____)>] ret_from_fork+0x10/0x20
unreferenced object 0xffff000200d90010 (size 16):
  comm "kworker/4:0", pid 42, jiffies 4294892753
  hex dump (first 16 bytes):
    e0 39 57 c1 00 00 ff ff 00 00 d9 00 02 00 ff ff  .9W.............
  backtrace (crc d4c89665):
    [<(____ptrval____)>] kmemleak_alloc+0x3c/0x50
    [<(____ptrval____)>] kmalloc_trace+0x20c/0x2e0
    [<(____ptrval____)>] __set_page_owner+0x1d0/0x2a0
    [<(____ptrval____)>] prep_new_page+0x108/0x138
    [<(____ptrval____)>] get_page_from_freelist+0x79c/0x16b8
    [<(____ptrval____)>] __alloc_pages+0x1bc/0x440
    [<(____ptrval____)>] new_slab+0x104/0x3c8
    [<(____ptrval____)>] ___slab_alloc+0x368/0xb20
    [<(____ptrval____)>] __slab_alloc.isra.0+0x3c/0x88
    [<(____ptrval____)>] kmalloc_trace+0x280/0x2e0
    [<(____ptrval____)>] __kthread_create_on_node+0x7c/0x190
    [<(____ptrval____)>] kthread_create_on_node+0x60/0x90
    [<(____ptrval____)>] create_worker+0xd0/0x278
    [<(____ptrval____)>] worker_thread+0x260/0x320
    [<(____ptrval____)>] kthread+0x130/0x148
    [<(____ptrval____)>] ret_from_fork+0x10/0x20

Thanks.

> Oscar Salvador (3):
>    mm,page_owner: Update metada for tail pages
>    mm,page_owner: Fix refcount imbalance
>    mm,page_owner: Fix accounting of pages when migrating
>
>   Documentation/mm/page_owner.rst |  73 +++++++------
>   mm/page_owner.c                 | 184 +++++++++++++++++++-------------
>   2 files changed, 146 insertions(+), 111 deletions(-)