Messages in this thread | | | Date | Wed, 15 Dec 2021 17:04:18 +0100 | Subject | Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping | From | David Hildenbrand <> |
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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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