+ mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch added to -mm tree

* + mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch added to -mm tree
@ 2020-03-26  0:35 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2020-03-26  0:35 UTC (permalink / raw)
  To: aneesh.kumar, bhe, dan.j.williams, mm-commits, mpe, sachinp


The patch titled
     Subject: mm/sparse: fix kernel crash with pfn_section_valid check
has been added to the -mm tree.  Its filename is
     mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch

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------------------------------------------------------
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Subject: mm/sparse: fix kernel crash with pfn_section_valid check

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.

Link: http://lkml.kernel.org/r/20200325031914.107660-1-aneesh.kumar@linux.ibm.com
Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/sparse.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/sparse.c~mm-sparse-fix-kernel-crash-with-pfn_section_valid-check
+++ a/mm/sparse.c
@@ -781,6 +781,8 @@ static void section_deactivate(unsigned
 			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)
_

Patches currently in -mm which might be from aneesh.kumar@linux.ibm.com are

mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch

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