Re: [PATCH v2] Fix "kmem -n" option to display memory blocks on Linux 6.3-rc1 and later

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On Fri, Mar 10, 2023 at 10:38 AM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx> wrote:
Kernel commit d2bf38c088e0 ("driver core: remove private pointer from
struct bus_type") removed the bus_type.p member, and the "kmem -n"
option fails with the following error before displaying memory block
information on Linux 6.3-rc1 and later kernels.

  kmem: invalid structure member offset: bus_type_p
        FILE: memory.c  LINE: 17852  FUNCTION: init_memory_block()

Search bus_kset.list instead for subsys_private of memory subsys.

Signed-off-by: Kazuhito Hagio <k-hagio-ab@xxxxxxx>
---
 defs.h    |  2 ++
 memory.c  | 63 +++++++++++++++++++++++++++++++++++++++++++++++++------
 symbols.c |  2 ++
 3 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/defs.h b/defs.h
index 1f2cf6e0ce01..12ad6aaa0998 100644
--- a/defs.h
+++ b/defs.h
@@ -2214,6 +2214,8 @@ struct offset_table {                    /* stash of commonly-used offsets */
        long inet6_ifaddr_if_list;
        long inet6_ifaddr_if_next;
        long in6_addr_in6_u;
+       long kset_kobj;
+       long subsys_private_subsys;
 };

 struct size_table {         /* stash of commonly-used sizes */
diff --git a/memory.c b/memory.c
index c4a6ecd18004..592a5ef49d50 100644
--- a/memory.c
+++ b/memory.c
@@ -17822,6 +17822,13 @@ static void
 init_memory_block_offset(void)
 {
        MEMBER_OFFSET_INIT(bus_type_p, "bus_type", "p");
+       if (INVALID_MEMBER(bus_type_p)) {
+               MEMBER_OFFSET_INIT(kset_list, "kset", "list");
+               MEMBER_OFFSET_INIT(kset_kobj, "kset", "kobj");
+               MEMBER_OFFSET_INIT(kobject_name, "kobject", "name");
+               MEMBER_OFFSET_INIT(kobject_entry, "kobject", "entry");
+               MEMBER_OFFSET_INIT(subsys_private_subsys, "subsys_private", "subsys");
+       }
        MEMBER_OFFSET_INIT(subsys_private_klist_devices,
                                "subsys_private", "klist_devices");
        MEMBER_OFFSET_INIT(klist_k_list, "klist", "k_list");
@@ -17842,15 +17849,60 @@ init_memory_block_offset(void)
 }

 static void
-init_memory_block(struct list_data *ld, int *klistcnt, ulong **klistbuf)
+init_memory_block(int *klistcnt, ulong **klistbuf)
 {
-       ulong memory_subsys = symbol_value("memory_subsys");
        ulong private, klist, start;
+       struct list_data list_data, *ld;
+
+       ld = &list_data;
+       private = 0;

        init_memory_block_offset();

-       readmem(memory_subsys + OFFSET(bus_type_p), KVADDR, &private,
-               sizeof(void *), "memory_subsys.private", FAULT_ON_ERROR);
+       /*
+        * v6.3-rc1
+        * d2bf38c088e0 driver core: remove private pointer from struct bus_type
+        */
+       if (INVALID_MEMBER(bus_type_p)) {
+               int i, cnt;
+               char buf[32];
+               ulong bus_kset, list, name;
+
+               BZERO(ld, sizeof(struct list_data));
+
+               get_symbol_data("bus_kset", sizeof(ulong), &bus_kset);
+               readmem(bus_kset + OFFSET(kset_list), KVADDR, &list,
+                       sizeof(ulong), "bus_kset.list", FAULT_ON_ERROR);
+
+               ld->flags |= LIST_ALLOCATE;
+               ld->start = list;
+               ld->end = bus_kset + OFFSET(kset_list);
+               ld->list_head_offset = OFFSET(kobject_entry);
+
+               cnt = do_list(ld);
+               for (i = 0; i < cnt; i++) {
+                       readmem(ld->list_ptr[i] + OFFSET(kobject_name), KVADDR, &name,
+                               sizeof(ulong), "kobject.name", FAULT_ON_ERROR);
+                       read_string(name, buf, sizeof(buf)-1);
+                       if (CRASHDEBUG(1))
+                               fprintf(fp, "kobject: %lx name: %s\n", ld->list_ptr[i], buf);
+                       if (STREQ(buf, "memory")) {

Thank you for the update, Kazu.
For the v2: Ack

Lianbo
 
+                               /* entry is subsys_private.subsys.kobj. See bus_to_subsys(). */
+                               private = ld->list_ptr[i] - OFFSET(kset_kobj)
+                                               - OFFSET(subsys_private_subsys);
+                               break;
+                       }
+               }
+               FREEBUF(ld->list_ptr);
+       } else {
+               ulong memory_subsys = symbol_value("memory_subsys");
+               readmem(memory_subsys + OFFSET(bus_type_p), KVADDR, &private,
+                       sizeof(void *), "memory_subsys.private", FAULT_ON_ERROR);
+       }
+
+       if (!private)
+               error(FATAL, "cannot determine subsys_private for memory.\n");
+
        klist = private + OFFSET(subsys_private_klist_devices) +
                                        OFFSET(klist_k_list);
        BZERO(ld, sizeof(struct list_data));
@@ -17875,7 +17927,6 @@ dump_memory_blocks(int initialize)
        ulong memory_block, device;
        ulong *klistbuf;
        int klistcnt, i;
-       struct list_data list_data;
        char mb_hdr[BUFSIZE];
        char paddr_hdr[BUFSIZE];
        char buf1[BUFSIZE];
@@ -17892,7 +17943,7 @@ dump_memory_blocks(int initialize)
        if (initialize)
                return;

-       init_memory_block(&list_data, &klistcnt, &klistbuf);
+       init_memory_block(&klistcnt, &klistbuf);

        if ((symbol_exists("memory_block_size_probed")) ||
            (MEMBER_EXISTS("memory_block", "end_section_nr")))
diff --git a/symbols.c b/symbols.c
index 28846d06273c..f0721023816d 100644
--- a/symbols.c
+++ b/symbols.c
@@ -10404,6 +10404,7 @@ dump_offset_table(char *spec, ulong makestruct)
                OFFSET(kobject_entry));
        fprintf(fp, "                     kset_list: %ld\n",
                OFFSET(kset_list));
+       fprintf(fp, "                     kset_kobj: %ld\n", OFFSET(kset_kobj));
        fprintf(fp, "            request_list_count: %ld\n",
                OFFSET(request_list_count));
        fprintf(fp, "             request_cmd_flags: %ld\n",
@@ -10441,6 +10442,7 @@ dump_offset_table(char *spec, ulong makestruct)
        fprintf(fp, "               blk_mq_tags_rqs: %ld\n",
                OFFSET(blk_mq_tags_rqs));

+       fprintf(fp, "         subsys_private_subsys: %ld\n", OFFSET(subsys_private_subsys));
        fprintf(fp, "  subsys_private_klist_devices: %ld\n",
                OFFSET(subsys_private_klist_devices));
        fprintf(fp, "                subsystem_kset: %ld\n",
--
2.31.1

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