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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.0 CC: , , , , , Subject: Re: [PATCH stable 4.14,4.19 1/1] mm: Fix page counter mismatch in shmem_mfill_atomic_pte Content-Language: en-US To: , , , References: <20220802013251.3022141-1-mawupeng1@huawei.com> From: mawupeng In-Reply-To: <20220802013251.3022141-1-mawupeng1@huawei.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.120] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500014.china.huawei.com (7.185.36.153) X-CFilter-Loop: Reflected ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660620433; a=rsa-sha256; cv=none; b=fysWZuvIyKpzjfdz3e6Q/ddF82ET3Q/+5xf4GzTrFDLnff9CCTPUW0EJIyKw1j/lBHL5iW OAnvF/CEmLbEv4lEkc8bPvkDT9gGmfkLMQIyVghfXdM62tNj1vejjrESWhBF0PsV+krb4W BhxPdN6hOJulRBXW86WXkIqfKVoD+rg= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of mawupeng1@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=mawupeng1@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660620433; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lMibiMLq/IhD3t+IOAc+ll2XbnDuar69Utfpr+Mpf70=; b=bnRO/FbJ5mBNUKlA7mTR7e2WhiRsy719htP/zy+wr04p2avHY+OBGYt7J3xJwU7bDUPTn5 kRFc8JSotO+uQIhO5AWtgUN02OiOZnuEz/FBjtC36eHDopuY6xlqMMEt/FPXQseqJvghXK fQcj1/KGYEuD0LxhgDXeVWxS5HcXa0k= Authentication-Results: imf14.hostedemail.com; dkim=none; spf=pass (imf14.hostedemail.com: domain of mawupeng1@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=mawupeng1@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspam-User: X-Stat-Signature: opspei4ocadk351e4gm6o81m9ita9nao X-Rspamd-Queue-Id: DBEE91001AC X-Rspamd-Server: rspam06 X-HE-Tag: 1660620432-594440 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Cc Greg On 2022/8/2 9:32, Wupeng Ma wrote: > From: Ma Wupeng > > 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. > > This will lead to page->memcg not null and will uncharge one more in put_page(). > The page counter will underflow to maximum value and trigger oom to kill all > process include sshd and leave system unaccessible. > > page->memcg is set in the following path: > mem_cgroup_commit_charge > commit_charge > page->mem_cgroup = memcg; > > extra uncharge will be done in the following path: > put_page > __put_page > __put_single_page > mem_cgroup_uncharge > if (!page->mem_cgroup) <-- should return here > return > uncharge_page > uncharge_batch > > To fix this, call mem_cgroup_commit_charge() at the end of this transaction to > make sure this transaction is really finished. > > Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support") > Signed-off-by: Ma Wupeng > --- > mm/shmem.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/shmem.c b/mm/shmem.c > index 0788616696dc..0b06724c189e 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -2339,8 +2339,6 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, > if (ret) > goto out_release_uncharge; > > - mem_cgroup_commit_charge(page, memcg, false, false); > - > _dst_pte = mk_pte(page, dst_vma->vm_page_prot); > if (dst_vma->vm_flags & VM_WRITE) > _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte)); > @@ -2366,6 +2364,8 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, > if (!pte_none(*dst_pte)) > goto out_release_uncharge_unlock; > > + mem_cgroup_commit_charge(page, memcg, false, false); > + > lru_cache_add_anon(page); > > spin_lock_irq(&info->lock);