* Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check
2020-03-26 13:32 [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
@ 2020-03-26 13:38 ` Baoquan He
2020-03-26 13:55 ` Michal Hocko
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Baoquan He @ 2020-03-26 13:38 UTC (permalink / raw)
To: Aneesh Kumar K.V
Cc: linux-mm, akpm, linux-kernel, mpe, linuxppc-dev, Sachin Sant,
Dan Williams, Pankaj Gupta, David Hildenbrand, Michal Hocko,
Wei Yang, Oscar Salvador, Mike Rapoport, stable
On 03/26/20 at 07:02pm, 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 <sachinp@linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> mm/sparse.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index aadb7298dcef..65599e8bd636 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -781,6 +781,12 @@ 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 so that valid_section()
> + * return false. This prevents code from dereferencing
> + * ms->usage array.
> + */
> + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> }
Reviewed-by: Baoquan He <bhe@redhat.com>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check
2020-03-26 13:32 [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
2020-03-26 13:38 ` Baoquan He
@ 2020-03-26 13:55 ` Michal Hocko
2020-03-26 16:04 ` Pankaj Gupta
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: Michal Hocko @ 2020-03-26 13:55 UTC (permalink / raw)
To: Aneesh Kumar K.V
Cc: linux-mm, akpm, linux-kernel, mpe, linuxppc-dev, Sachin Sant,
Baoquan He, Dan Williams, Pankaj Gupta, David Hildenbrand,
Wei Yang, Oscar Salvador, Mike Rapoport, stable
On Thu 26-03-20 19:02:35, 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.
I believe that the necessity of clearing the section before the tear
down is worth a comment into the code. Because this is just way to easy
to miss or not be aware at all while looking into the code without git
balme.
> Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case")
> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!
> ---
> mm/sparse.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index aadb7298dcef..65599e8bd636 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -781,6 +781,12 @@ 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 so that valid_section()
> + * return false. This prevents code from dereferencing
> + * ms->usage array.
> + */
> + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> }
>
> if (section_is_early && memmap)
> --
> 2.25.1
>
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check
2020-03-26 13:32 [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
2020-03-26 13:38 ` Baoquan He
2020-03-26 13:55 ` Michal Hocko
@ 2020-03-26 16:04 ` Pankaj Gupta
2020-03-26 22:12 ` Wei Yang
2020-03-27 9:42 ` David Hildenbrand
4 siblings, 0 replies; 6+ messages in thread
From: Pankaj Gupta @ 2020-03-26 16:04 UTC (permalink / raw)
To: Aneesh Kumar K.V
Cc: linux-mm, Andrew Morton, linux-kernel, mpe, linuxppc-dev,
Sachin Sant, Baoquan He, Dan Williams, David Hildenbrand,
Michal Hocko, Wei Yang, Oscar Salvador, Mike Rapoport, stable
>
> 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 <sachinp@linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> mm/sparse.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index aadb7298dcef..65599e8bd636 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -781,6 +781,12 @@ 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 so that valid_section()
> + * return false. This prevents code from dereferencing
> + * ms->usage array.
> + */
> + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> }
>
> if (section_is_early && memmap)
> --
Agree with Michal, comment for clearing the section would be nicer.
Fix looks good to me.
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> 2.25.1
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check
2020-03-26 13:32 [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
` (2 preceding siblings ...)
2020-03-26 16:04 ` Pankaj Gupta
@ 2020-03-26 22:12 ` Wei Yang
2020-03-27 9:42 ` David Hildenbrand
4 siblings, 0 replies; 6+ messages in thread
From: Wei Yang @ 2020-03-26 22:12 UTC (permalink / raw)
To: Aneesh Kumar K.V
Cc: linux-mm, akpm, linux-kernel, mpe, linuxppc-dev, Sachin Sant,
Baoquan He, Dan Williams, Pankaj Gupta, David Hildenbrand,
Michal Hocko, Wei Yang, Oscar Salvador, Mike Rapoport, stable
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 <sachinp@linux.vnet.ibm.com>
>Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
>Cc: Baoquan He <bhe@redhat.com>
>Cc: Michael Ellerman <mpe@ellerman.id.au>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
>Cc: David Hildenbrand <david@redhat.com>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: Mike Rapoport <rppt@linux.ibm.com>
>Cc: <stable@vger.kernel.org>
>Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
--
Wei Yang
Help you, Help me
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check
2020-03-26 13:32 [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
` (3 preceding siblings ...)
2020-03-26 22:12 ` Wei Yang
@ 2020-03-27 9:42 ` David Hildenbrand
4 siblings, 0 replies; 6+ messages in thread
From: David Hildenbrand @ 2020-03-27 9:42 UTC (permalink / raw)
To: Aneesh Kumar K.V, linux-mm, akpm
Cc: linux-kernel, mpe, linuxppc-dev, Sachin Sant, Baoquan He,
Dan Williams, Pankaj Gupta, Michal Hocko, Wei Yang,
Oscar Salvador, Mike Rapoport, stable
On 26.03.20 14:32, 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 <sachinp@linux.vnet.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> mm/sparse.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index aadb7298dcef..65599e8bd636 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -781,6 +781,12 @@ 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 so that valid_section()
> + * return false. This prevents code from dereferencing
s/return/returns/
> + * ms->usage array.
maybe "(see pfn_section_valid())"
> + */
> + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
--
Thanks,
David / dhildenb
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