Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check

On 03/25/20 at 03:06pm, Baoquan He wrote:

On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote:

quoted

 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