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Wed, 25 Mar 2020 07:06:48 +0000 (UTC) Received: from localhost (ovpn-12-88.pek2.redhat.com [10.72.12.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A43DE91D82; Wed, 25 Mar 2020 07:06:46 +0000 (UTC) Date: Wed, 25 Mar 2020 15:06:43 +0800 From: Baoquan He To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, Sachin Sant , dan.j.williams@intel.com Subject: Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check Message-ID: <20200325070643.GH3039@MiWiFi-R3L-srv> References: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325031914.107660-1-aneesh.kumar@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 03/25/20 at 08:49am, 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 > > 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. > > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > Cc: Baoquan He > Reported-by: Sachin Sant > Signed-off-by: Aneesh Kumar K.V Maybe add Sachin's Tested-by, Sachin has tested and confirmed this fix works. > --- > mm/sparse.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/sparse.c b/mm/sparse.c > index aadb7298dcef..3012d1f3771a 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -781,6 +781,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, > ms->usage = NULL; > } > memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr); > + /* Mark the section invalid */ > + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP; Not sure if we should add checking in valid_section() or pfn_valid(), e.g check ms->usage validation too. Otherwise, this fix looks good to me. Reviewed-by: Baoquan He