Messages in this thread | | | Date | Wed, 15 Dec 2021 16:02:55 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping |
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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.
-- Catalin
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