| Message ID | 20200325031914.107660-1-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/sparse: Fix kernel crash with pfn_section_valid check | expand |
Hi Andrew, Can this be merged for v5.6? Without this most persistent memory commands (ndctl) will result in a kernel crash on v5.6. -aneesh "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes: > 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 <bhe@redhat.com> > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > --- > 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; > } > > if (section_is_early && memmap) > -- > 2.25.1
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 <bhe@redhat.com> > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> 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 <bhe@redhat.com>
On 03/25/20 at 03:06pm, Baoquan He wrote: > On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote: > > 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. With SPASEMEM_VMEMAP enabled, we should do validation check on ms->usage before checking any subsection is valid. Since now we do have case in which ms->usage is released, people still try to check it. diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index f0a2c184eb9a..d79bd938852e 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1306,6 +1306,8 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) { int idx = subsection_map_index(pfn); + if (!ms->usage) + return 0; return test_bit(idx, ms->usage->subsection_map); } #else
On 3/25/20 1:07 PM, Baoquan He wrote: > On 03/25/20 at 03:06pm, Baoquan He wrote: >> On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote: > >>> 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. > > With SPASEMEM_VMEMAP enabled, we should do validation check on ms->usage > before checking any subsection is valid. Since now we do have case > in which ms->usage is released, people still try to check it. > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index f0a2c184eb9a..d79bd938852e 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1306,6 +1306,8 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > { > int idx = subsection_map_index(pfn); > > + if (!ms->usage) > + return 0; > return test_bit(idx, ms->usage->subsection_map); > } > #else > We always check for section valid, before we check if pfn_section_valid(). static inline int pfn_valid(unsigned long pfn) struct mem_section *ms; if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) return 0; ms = __nr_to_section(pfn_to_section_nr(pfn)); if (!valid_section(ms)) return 0; /* * Traditionally early sections always returned pfn_valid() for * the entire section-sized span. */ return early_section(ms) || pfn_section_valid(ms, pfn); } IMHO adding that if (!ms->usage) is redundant. -aneesh
On 03/25/20 at 01:42pm, Aneesh Kumar K.V wrote: > On 3/25/20 1:07 PM, Baoquan He wrote: > > On 03/25/20 at 03:06pm, Baoquan He wrote: > > > On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote: > > > > > > 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. > > > > With SPASEMEM_VMEMAP enabled, we should do validation check on ms->usage > > before checking any subsection is valid. Since now we do have case > > in which ms->usage is released, people still try to check it. > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index f0a2c184eb9a..d79bd938852e 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -1306,6 +1306,8 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > > { > > int idx = subsection_map_index(pfn); > > + if (!ms->usage) > > + return 0; > > return test_bit(idx, ms->usage->subsection_map); > > } > > #else > > > > We always check for section valid, before we check if pfn_section_valid(). > > static inline int pfn_valid(unsigned long pfn) > > struct mem_section *ms; > > if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS) > return 0; > ms = __nr_to_section(pfn_to_section_nr(pfn)); > if (!valid_section(ms)) > return 0; > /* > * Traditionally early sections always returned pfn_valid() for > * the entire section-sized span. > */ > return early_section(ms) || pfn_section_valid(ms, pfn); > } > > > IMHO adding that if (!ms->usage) is redundant. Yeah, I tend to agree. Consider this happens in the only small window between ms->usage releasing and ms->section_mem_map releasing when removing a section. Just thought adding this check to enhance it even though we have had your fix, because we only check ms->section_mem_map in valid_section(). Anyway, your fix looks good to me, see if other people have any comment. Thanks Baoquan
On Wed, 25 Mar 2020 08:49:14 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote: > Fixes the below crash (cc's added) > 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") d41e2f3bd546 had cc:stable, so I shall add cc:stable to this one as well. > Cc: Baoquan He <bhe@redhat.com> > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > --- > 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; > } > > if (section_is_early && memmap)
On Wed 25-03-20 08:49:14, 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 It would be great to match this to the specific source code. > __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. I am sorry, I haven't noticed that during the review of the commit mentioned above. This is all subtle as hell, I have to say. Why do we have to free usage before deactivaing section memmap? Now that we have a late section_mem_map reset shouldn't we tear down the usage in the same branch? > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > Cc: Baoquan He <bhe@redhat.com> > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > --- > 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; Btw. this comment is not really helping at all. /* * section->usage is gone and VMEMMAP's pfn_valid depens * on it (see pfn_section_valid) */ > } > > if (section_is_early && memmap) > -- > 2.25.1 >
On 3/26/20 3:10 PM, Michal Hocko wrote: > On Wed 25-03-20 08:49:14, 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 > > It would be great to match this to the specific source code. The crash is due to NULL dereference at test_bit(idx, ms->usage->subsection_map); due to ms->usage = NULL; that is explained in later part of the commit. > >> __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. > > I am sorry, I haven't noticed that during the review of the commit > mentioned above. This is all subtle as hell, I have to say. > > Why do we have to free usage before deactivaing section memmap? Now that > we have a late section_mem_map reset shouldn't we tear down the usage in > the same branch? > We still need to make the section invalid before we call into depopulate_section_memmap(). Because architecture like powerpc can share vmemmap area across sections (16MB mapping of vmemmap area) and we use vmemmap_popluated() to make that decision. >> Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") >> Cc: Baoquan He <bhe@redhat.com> >> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> >> --- >> 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; > > Btw. this comment is not really helping at all. That is marking the section invalid so that static inline int valid_section(struct mem_section *section) { return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP)); } returns false. > /* > * section->usage is gone and VMEMMAP's pfn_valid depens > * on it (see pfn_section_valid) > */ >> } >> >> if (section_is_early && memmap) >> -- >> 2.25.1 >> >
On Thu 26-03-20 15:26:22, Aneesh Kumar K.V wrote: > On 3/26/20 3:10 PM, Michal Hocko wrote: > > On Wed 25-03-20 08:49:14, 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 > > > > It would be great to match this to the specific source code. > > The crash is due to NULL dereference at > > test_bit(idx, ms->usage->subsection_map); due to ms->usage = NULL; It would be nice to call that out here as well [...] > > Why do we have to free usage before deactivaing section memmap? Now that > > we have a late section_mem_map reset shouldn't we tear down the usage in > > the same branch? > > > > We still need to make the section invalid before we call into > depopulate_section_memmap(). Because architecture like powerpc can share > vmemmap area across sections (16MB mapping of vmemmap area) and we use > vmemmap_popluated() to make that decision. This should be noted in a comment as well. > > > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > > > Cc: Baoquan He <bhe@redhat.com> > > > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > > > --- > > > 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; > > > > Btw. this comment is not really helping at all. > > That is marking the section invalid so that > > static inline int valid_section(struct mem_section *section) > { > return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP)); > } > > > returns false. Yes that is obvious once you are clear where to look. I was really hoping for a comment that would simply point you to the right direcection without chasing SECTION_HAS_MEM_MAP usage. This code is subtle and useful comments, even when they state something that is obvious to you _right_now_, can be really helpful. Thanks!
On Thu 26-03-20 11:16:33, Michal Hocko wrote: > On Thu 26-03-20 15:26:22, Aneesh Kumar K.V wrote: > > On 3/26/20 3:10 PM, Michal Hocko wrote: > > > On Wed 25-03-20 08:49:14, 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 > > > > > > It would be great to match this to the specific source code. > > > > The crash is due to NULL dereference at > > > > test_bit(idx, ms->usage->subsection_map); due to ms->usage = NULL; > > It would be nice to call that out here as well > > [...] > > > Why do we have to free usage before deactivaing section memmap? Now that > > > we have a late section_mem_map reset shouldn't we tear down the usage in > > > the same branch? > > > > > > > We still need to make the section invalid before we call into > > depopulate_section_memmap(). Because architecture like powerpc can share > > vmemmap area across sections (16MB mapping of vmemmap area) and we use > > vmemmap_popluated() to make that decision. > > This should be noted in a comment as well. > > > > > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > > > > Cc: Baoquan He <bhe@redhat.com> > > > > Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> > > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> > > > > --- > > > > 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; > > > > > > Btw. this comment is not really helping at all. > > > > That is marking the section invalid so that > > > > static inline int valid_section(struct mem_section *section) > > { > > return (section && (section->section_mem_map & SECTION_HAS_MEM_MAP)); > > } > > > > > > returns false. > > Yes that is obvious once you are clear where to look. I was really > hoping for a comment that would simply point you to the right > direcection without chasing SECTION_HAS_MEM_MAP usage. This code is > subtle and useful comments, even when they state something that is > obvious to you _right_now_, can be really helpful. Btw. forgot to add. With the improved comment feel free to add Acked-by: Michal Hocko <mhocko@suse.com>
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; } if (section_is_early && memmap)
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 <bhe@redhat.com> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> --- mm/sparse.c | 2 ++ 1 file changed, 2 insertions(+)