Re: [PATCH stable 4.14,4.19 1/1] mm: Fix page counter mismatch in shmem_mfill_atomic_pte

[mawupeng]

On 2022/8/16 13:31, Greg KH wrote:
> On Tue, Aug 16, 2022 at 11:27:08AM +0800, mawupeng wrote:
>> Cc Greg
> 
> Cc Greg for what?  I have no context here at all as to what you want me
> to do..

We found a bug related to memory cgroup counter in stable 4.14/4.19.
shmem_mfill_atomic_pte() wrongly called mem_cgroup_cancel_charge() in "success"
path, it should mem_cgroup_uncharge() to dec memory counter instead.
mem_cgroup_cancel_charge() should only be used if this transaction is
unsuccessful and mem_cgroup_uncharge() is used to do this if this transaction
succeed.

Commit 3fea5a499d57 ("mm: memcontrol: convert page cache to a new mem_cgroup_charge() API")
in v5.8-rc1 change is charge/uncharge/cancel logic so don't have this
problem.

This counter will underflow to negative maximum value and trigger oom to kill all
process include sshd and leave system unaccessible.

The reason cc you is that we want to merge this bugfix into stable 4.14/4.19.

The error call trace:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 17127 at mm/page_counter.c:62 page_counter_cancel+0x57/0x90
RIP: 0010:page_counter_cancel+0x57/0x90
Call Trace:
  page_counter_uncharge+0x33/0x60
  uncharge_batch+0xb5/0x5f0
  mem_cgroup_uncharge_list+0x102/0x170
  release_pages+0x814/0xcc0
  tlb_flush_mmu_free+0xa9/0x140
  arch_tlb_finish_mmu+0xa4/0x140
  tlb_finish_mmu+0x90/0xf0
  exit_mmap+0x264/0x4b0

> 
> totally confused,
> 
> greg k-h