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    mm: call page_ext_init() after all struct pages are initialized · b8f1a75d
    Yang Shi authored
    When DEFERRED_STRUCT_PAGE_INIT is enabled, just a subset of memmap at
    boot are initialized, then the rest are initialized in parallel by
    starting one-off "pgdatinitX" kernel thread for each node X.
    If page_ext_init is called before it, some pages will not have valid
    extension, this may lead the below kernel oops when booting up kernel:
      BUG: unable to handle kernel NULL pointer dereference at           (null)
      IP: [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
      PGD 0
      Modules linked in:
      CPU: 11 PID: 106 Comm: pgdatinit1 Not tainted 4.6.0-rc5-next-20160427 #26
      Hardware name: Intel Corporation S5520HC/S5520HC, BIOS S5500.86B.01.10.0025.030220091519 03/02/2009
      task: ffff88017c080040 ti: ffff88017c084000 task.ti: ffff88017c084000
      RIP: 0010:[<ffffffff8118d982>]  [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
      RSP: 0000:ffff88017c087c48  EFLAGS: 00010046
      RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
      RDX: 0000000000000980 RSI: 0000000000000080 RDI: 0000000000660401
      RBP: ffff88017c087cd0 R08: 0000000000000401 R09: 0000000000000009
      R10: ffff88017c080040 R11: 000000000000000a R12: 0000000000000400
      R13: ffffea0019810000 R14: ffffea0019810040 R15: ffff88066cfe6080
      FS:  0000000000000000(0000) GS:ffff88066cd40000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 0000000000000000 CR3: 0000000002406000 CR4: 00000000000006e0
      Call Trace:
      Code: 49 89 d4 48 c1 e0 06 49 01 c5 e9 de fe ff ff 4c 89 f7 44 89 4d b8 4c 89 45 c0 44 89 5d c8 48 89 4d d0 e8 62 c7 07 00 48 8b 4d d0 <48> 8b 00 44 8b 5d c8 4c 8b 45 c0 44 8b 4d b8 a8 02 0f 84 05 ff
      RIP  [<ffffffff8118d982>] free_pcppages_bulk+0x2d2/0x8d0
       RSP <ffff88017c087c48>
      CR2: 0000000000000000
    Move page_ext_init() after page_alloc_init_late() to make sure page extension
    is setup for all pages.
    Signed-off-by: default avatarYang Shi <>
    Cc: Joonsoo Kim <>
    Signed-off-by: default avatarAndrew Morton <>
    Signed-off-by: default avatarLinus Torvalds <>