Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-12-15 16:03:05
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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:quoted
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 <redacted>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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel