driver/firmware/memmap: don't create memmap sysfs of same firmware_map_entry

By the following commits, we prevented from allocating firmware_map_entry of same memory range:
f0093ede: drivers/firmware/memmap.c: don't allocate firmware_map_entry
of same memory range
49c8b24d: drivers/firmware/memmap.c: pass the correct argument to
firmware_map_find_entry_bootmem()

But it's not enough. When PNP0C80 device is added by acpi_scan_init(), memmap sysfses of same firmware_map_entry are created twice as follows:

  # cat /sys/firmware/memmap/*/start
  0x40000000000
  0x60000000000
  0x4a837000
  0x4a83a000
  0x4a8b5000
  ...
  0x40000000000
  0x60000000000
  ...

The flows of the issues are as follows:

1. e820_reserve_resources() allocates firmware_map_entrys of all memory ranges defined in e820. And, these firmware_map_entrys are linked with map_entries list.

map_entries -> entry 1 -> ... -> entry N

2. When PNP0C80 device is limited by mem= boot option, acpi_scan_init() added the memory device. In this case, firmware_map_add_hotplug() allocates firmware_map_entry and creates memmap sysfs.

map_entries -> entry 1 -> ... -> entry N -> entry N+1
| memmap 1

3. firmware_memmap_init() creates memmap sysfses of firmware_map_entrys linked with map_entries.

map_entries -> entry 1 -> ... -> entry N -> entry N+1
| | |
memmap 2 memmap N+1 memmap 1
memmap N+2

So while hot removing the PNP0C80 device, kernel panic occurs as follows:

     BUG: unable to handle kernel paging request at 00000001003e000b
      IP: sysfs_open_file+0x46/0x2b0
      PGD 203a89fe067 PUD 0
      Oops: 0000 [#1] SMP
      ...
      Call Trace:
        do_dentry_open+0x1ef/0x2a0
        finish_open+0x31/0x40
        do_last+0x57c/0x1220
        path_openat+0xc2/0x4c0
        do_filp_open+0x4b/0xb0
        do_sys_open+0xf3/0x1f0
        SyS_open+0x1e/0x20
        system_call_fastpath+0x16/0x1b

The patch adds a check of confirming whether memmap sysfs of firmware_map_entry has been created, and does not create memmap sysfs of same firmware_map_entry.

---
 drivers/firmware/memmap.c | 3 +++
 1 file changed, 3 insertions(+)

index 79f18e6..cc016c6 100644
@@ -184,6 +184,9 @@ static int add_sysfs_fw_map_entry(struct firmware_map_entry *entry)
 	static int map_entries_nr;
 	static struct kset *mmap_kset;
 
+	if (entry->kobj.state_in_sysfs)
+		return -EEXIST;
+
 	if (!mmap_kset) {
 		mmap_kset = kset_create_and_add("memmap", NULL, firmware_kobj);
 		if (!mmap_kset)

1.8.3.1

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