Messages in this thread | | | From | Jianyong Wu <> | Subject | RE: [PATCH v2] arm64/mm: avoid fixmap race condition when create pud mapping | Date | Thu, 16 Dec 2021 03:00:17 +0000 |
| |
Thanks Qian to report this. I will change to mutex lock and resend it later.
Thanks Jianyong
> -----Original Message----- > From: David Hildenbrand <david@redhat.com> > Sent: Thursday, December 16, 2021 12:04 AM > 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 <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 > <Justin.He@arm.com>; nd <nd@arm.com> > Subject: Re: [PATCH v2] arm64/mm: avoid fixmap race condition when create > pud mapping > > 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
| |