linux-kernel - Re: [PATCH stable 4.14,4.19 1/1] mm: Fix page counter mismatch in shmem_mfill_atomic

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Date:   Tue, 16 Aug 2022 09:15:18 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     mawupeng <mawupeng1@...wei.com>
Cc:     rppt@...ux.vnet.ibm.com, hughd@...gle.com, aarcange@...hat.com,
        hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com,
        willy@...radead.org
Subject: Re: [PATCH stable 4.14,4.19 1/1] mm: Fix page counter mismatch in
 shmem_mfill_atomic_pte

On Tue, Aug 16, 2022 at 03:04:08PM +0800, mawupeng wrote:
> 
> 
> 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.

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>