Kernel commit 869176a09606 ("mm/vmalloc.c: add flags to mark vm_map_ram
area"), which is contained in Linux 6.3 and later, added "flags" member
to struct vmap_area.  This was the revival of the "flags" member as
kernel commit 688fcbfc06e4 had eliminated it before.

As a result, crash started to use the old procedure using the member and
displays no vmalloc'd regions, because it does not have the same flag
value as the old one.

    crash> kmem -v
       VMAP_AREA         VM_STRUCT                 ADDRESS RANGE                SIZE
    crash>

To fix this, also check if vmap_area.purge_list exists, which was
introduced with the flags and removed later, to determine that the flags
member is the old one.

Related vmap_area history:
 v2.6.28 db64fe02258f introduced vmap_area with flags and purge_list
 v5.4    688fcbfc06e4 removed flags
 v5.11   96e2db456135 removed purge_list
 v6.3    869176a09606 added flags again

Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
---
 defs.h    | 1 +
 memory.c  | 4 +++-
 symbols.c | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/defs.h b/defs.h
index 21cc760444d1..bfa07c3f5150 100644
--- a/defs.h
+++ b/defs.h
@@ -2216,6 +2216,7 @@ struct offset_table {                    /* stash of commonly-used offsets */
        long in6_addr_in6_u;
        long kset_kobj;
        long subsys_private_subsys;
+       long vmap_area_purge_list;
 };

 struct size_table {         /* stash of commonly-used sizes */
diff --git a/memory.c b/memory.c
index 953fc380c03c..15fa8b2f08f1 100644
--- a/memory.c
+++ b/memory.c
@@ -429,6 +429,7 @@ vm_init(void)
        MEMBER_OFFSET_INIT(vmap_area_vm, "vmap_area", "vm");
        if (INVALID_MEMBER(vmap_area_vm))
                MEMBER_OFFSET_INIT(vmap_area_vm, "vmap_area", "private");
+       MEMBER_OFFSET_INIT(vmap_area_purge_list, "vmap_area", "purge_list");
        STRUCT_SIZE_INIT(vmap_area, "vmap_area");
        if (VALID_MEMBER(vmap_area_va_start) &&
            VALID_MEMBER(vmap_area_va_end) &&
@@ -9063,7 +9064,8 @@ dump_vmap_area(struct meminfo *vi)
                readmem(ld->list_ptr[i], KVADDR, vmap_area_buf,
                         SIZE(vmap_area), "vmap_area struct", FAULT_ON_ERROR);

-               if (VALID_MEMBER(vmap_area_flags)) {
+               if (VALID_MEMBER(vmap_area_flags) &&
+                   VALID_MEMBER(vmap_area_purge_list)) {
                        flags = ULONG(vmap_area_buf + OFFSET(vmap_area_flags));
                        if (flags != VM_VM_AREA)
                                continue;
diff --git a/symbols.c b/symbols.c
index f0721023816d..7b1d59203b90 100644
--- a/symbols.c
+++ b/symbols.c
@@ -9169,6 +9169,7 @@ dump_offset_table(char *spec, ulong makestruct)
                OFFSET(vmap_area_vm));
        fprintf(fp, "               vmap_area_flags: %ld\n",
                OFFSET(vmap_area_flags));
+       fprintf(fp, "          vmap_area_purge_list: %ld\n", OFFSET(vmap_area_purge_list));

        fprintf(fp, "         module_size_of_struct: %ld\n",
                OFFSET(module_size_of_struct));
--
2.31.1