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charset=us-ascii Content-Disposition: inline In-Reply-To: <20200326133235.343616-1-aneesh.kumar@linux.ibm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 26, 2020 at 07:02:35PM +0530, Aneesh Kumar K.V wrote: >Fixes the below crash > >BUG: Kernel NULL pointer dereference on read at 0x00000000 >Faulting instruction address: 0xc000000000c3447c >Oops: Kernel access of bad area, sig: 11 [#1] >LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries >CPU: 11 PID: 7519 Comm: lt-ndctl Not tainted 5.6.0-rc7-autotest #1 >... >NIP [c000000000c3447c] vmemmap_populated+0x98/0xc0 >LR [c000000000088354] vmemmap_free+0x144/0x320 >Call Trace: > section_deactivate+0x220/0x240 > __remove_pages+0x118/0x170 > arch_remove_memory+0x3c/0x150 > memunmap_pages+0x1cc/0x2f0 > devm_action_release+0x30/0x50 > release_nodes+0x2f8/0x3e0 > device_release_driver_internal+0x168/0x270 > unbind_store+0x130/0x170 > drv_attr_store+0x44/0x60 > sysfs_kf_write+0x68/0x80 > kernfs_fop_write+0x100/0x290 > __vfs_write+0x3c/0x70 > vfs_write+0xcc/0x240 > ksys_write+0x7c/0x140 > system_call+0x5c/0x68 > >The crash is due to NULL dereference at > >test_bit(idx, ms->usage->subsection_map); due to ms->usage = NULL; in pfn_section_valid() > >With commit: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") >section_mem_map is set to NULL after depopulate_section_mem(). This >was done so that pfn_page() can work correctly with kernel config that disables >SPARSEMEM_VMEMMAP. With that config pfn_to_page does > > __section_mem_map_addr(__sec) + __pfn; >where > >static inline struct page *__section_mem_map_addr(struct mem_section *section) >{ > unsigned long map = section->section_mem_map; > map &= SECTION_MAP_MASK; > return (struct page *)map; >} > >Now with SPASEMEM_VMEMAP enabled, mem_section->usage->subsection_map is used to >check the pfn validity (pfn_valid()). Since section_deactivate release >mem_section->usage if a section is fully deactivated, pfn_valid() check after >a subsection_deactivate cause a kernel crash. > >static inline int pfn_valid(unsigned long pfn) >{ >... > return early_section(ms) || pfn_section_valid(ms, pfn); >} > >where > >static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) >{ > int idx = subsection_map_index(pfn); > > return test_bit(idx, ms->usage->subsection_map); >} > >Avoid this by clearing SECTION_HAS_MEM_MAP when mem_section->usage is freed. >For architectures like ppc64 where large pages are used for vmmemap mapping (16MB), >a specific vmemmap mapping can cover multiple sections. Hence before a vmemmap >mapping page can be freed, the kernel needs to make sure there are no valid sections >within that mapping. Clearing the section valid bit before >depopulate_section_memap enables this. > >Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") >Reported-by: Sachin Sant >Tested-by: Sachin Sant >Cc: Baoquan He >Cc: Michael Ellerman >Cc: Dan Williams >Cc: Pankaj Gupta >Cc: David Hildenbrand >Cc: Michal Hocko >Cc: Wei Yang >Cc: Oscar Salvador >Cc: Mike Rapoport >Cc: >Signed-off-by: Aneesh Kumar K.V Reviewed-by: Wei Yang -- Wei Yang Help you, Help me