From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Qian Cai <quic_qiancai@quicinc.com>
Cc: Jianyong Wu <jianyong.wu@arm.com>,
will@kernel.org, anshuman.khandual@arm.com,
akpm@linux-foundation.org, ardb@kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, gshan@redhat.com,
justin.he@arm.com, nd@arm.com
Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping
Date: Wed, 15 Dec 2021 17:04:18 +0100 [thread overview]
Message-ID: <ccbb3a1f-856c-5879-acbc-fbaff9eb61de@redhat.com> (raw)
In-Reply-To: <YboRr0BCgjAbYdHe@arm.com>
On 15.12.21 17:02, Catalin Marinas wrote:
> On Wed, Dec 15, 2021 at 09:13:37AM -0500, Qian Cai wrote:
>> On Fri, Dec 10, 2021 at 05:54:32PM +0800, Jianyong Wu wrote:
>>> fixmap is a global resource and is used recursively in create pud mapping.
>>> It may lead to race condition when alloc_init_pud is called concurrently.
>>>
>>> Fox example:
>>> alloc_init_pud is called when kernel_init. If memory hotplug
>>> thread, which will also call alloc_init_pud, happens during
>>> kernel_init, the race for fixmap occurs.
>>>
>>> The race condition flow can be:
>>>
>>> *************** begin **************
>>>
>>> kerenl_init thread virtio-mem workqueue thread
>>> ================== ======== ==================
>>> alloc_init_pud(...)
>>> pudp = pud_set_fixmap_offset(..) alloc_init_pud(...)
>>> ... ...
>>> READ_ONCE(*pudp) //OK! pudp = pud_set_fixmap_offset(
>>> ... ...
>>> pud_clear_fixmap() //fixmap break
>>> READ_ONCE(*pudp) //CRASH!
>>>
>>> **************** end ***************
>>>
>>> Hence, a spin lock is introduced to protect the fixmap during create pdg
>>> mapping.
>>>
>>> Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
>>
>> I am afraid there is a problem to take a spinlock there.
>>
>> node 0 deferred pages initialised in 2740ms
>> pgdatinit0 (176) used greatest stack depth: 59184 bytes left
>> devtmpfs: initialized
>> KASLR disabled due to lack of seed
>> BUG: sleeping function called from invalid context at mm/page_alloc.c:5151
>
> Thanks for the report. Definitely a bug, GFP_KERNEL_ACCOUNT allows for
> the page allocator to sleep. I'll drop the patch from the arm64
> for-next/fixes branch for now and sort it out later.
>
Sounds like we need a mutex then.
--
Thanks,
David / dhildenb
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next prev parent reply other threads:[~2021-12-15 16:07 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 9:54 [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping Jianyong Wu
2021-12-10 11:22 ` Catalin Marinas
2021-12-13 5:24 ` Jianyong Wu
2021-12-13 6:56 ` Anshuman Khandual
2021-12-13 7:27 ` Jianyong Wu
2021-12-13 7:37 ` David Hildenbrand
2021-12-13 9:57 ` Catalin Marinas
2021-12-13 10:16 ` Anshuman Khandual
2021-12-13 10:35 ` Ard Biesheuvel
2021-12-13 13:45 ` Will Deacon
2021-12-13 14:01 ` Ard Biesheuvel
2021-12-13 16:42 ` Will Deacon
2021-12-15 14:13 ` Qian Cai
2021-12-15 16:02 ` Catalin Marinas
2021-12-15 16:04 ` David Hildenbrand [this message]
2021-12-16 3:00 ` Jianyong Wu
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