One of my testboxes triggered this nasty stack overflow crash
during SCSI probing:

[    5.874004] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
[    5.875004] device: 'sda': device_add
[    5.878004] BUG: unable to handle kernel NULL pointer dereference at 00000a0c
[    5.878004] IP: [<b1008321>] print_context_stack+0x81/0x110
[    5.878004] *pde = 00000000
[    5.878004] Thread overran stack, or stack corrupted
[    5.878004] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[    5.878004] last sysfs file:
[    5.878004]
[    5.878004] Pid: 1, comm: swapper Not tainted (2.6.31-rc6-tip-01272-g9919e28-dirty #5685)
[    5.878004] EIP: 0060:[<b1008321>] EFLAGS: 00010083 CPU: 0
[    5.878004] EIP is at print_context_stack+0x81/0x110
[    5.878004] EAX: cf8a3000 EBX: cf8a3fe4 ECX: 00000049 EDX: 00000000
[    5.878004] ESI: b1cfce84 EDI: 00000000 EBP: cf8a3018 ESP: cf8a2ff4
[    5.878004]  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[    5.878004] Process swapper (pid: 1, ti=cf8a2000 task=cf8a8000 task.ti=cf8a3000)
[    5.878004] Stack:
[    5.878004]  b1004867 fffff000 cf8a3ffc
[    5.878004] Call Trace:
[    5.878004]  [<b1004867>] ? kernel_thread_helper+0x7/0x10
[    5.878004] BUG: unable to handle kernel NULL pointer dereference at 00000a0c
[    5.878004] IP: [<b1008321>] print_context_stack+0x81/0x110
[    5.878004] *pde = 00000000
[    5.878004] Thread overran stack, or stack corrupted
[    5.878004] Oops: 0000 [#2] PREEMPT SMP DEBUG_PAGEALLOC

The oops did not reveal any more details about the real stack
that we have and the system got into an infinite loop of
recursive pagefaults.

So i booted with CONFIG_STACK_TRACER=y and the 'stacktrace' boot
parameter. The box did not crash (timings/conditions probably
changed a tiny bit to trigger the catastrophic crash), but the
/debug/tracing/stack_trace file was rather revealing:

        Depth    Size   Location    (72 entries)
        -----    ----   --------
  0)     3704      52   __change_page_attr+0xb8/0x290
  1)     3652      24   __change_page_attr_set_clr+0x43/0x90
  2)     3628      60   kernel_map_pages+0x108/0x120
  3)     3568      40   prep_new_page+0x7d/0x130
  4)     3528      84   get_page_from_freelist+0x106/0x420
  5)     3444     116   __alloc_pages_nodemask+0xd7/0x550
  6)     3328      36   allocate_slab+0xb1/0x100
  7)     3292      36   new_slab+0x1c/0x160
  8)     3256      36   __slab_alloc+0x133/0x2b0
  9)     3220       4   kmem_cache_alloc+0x1bb/0x1d0
 10)     3216     108   create_object+0x28/0x250
 11)     3108      40   kmemleak_alloc+0x81/0xc0
 12)     3068      24   kmem_cache_alloc+0x162/0x1d0
 13)     3044      52   scsi_pool_alloc_command+0x29/0x70
 14)     2992      20   scsi_host_alloc_command+0x22/0x70
 15)     2972      24   __scsi_get_command+0x1b/0x90
 16)     2948      28   scsi_get_command+0x35/0x90
 17)     2920      24   scsi_setup_blk_pc_cmnd+0xd4/0x100
 18)     2896     128   sd_prep_fn+0x332/0xa70
 19)     2768      36   blk_peek_request+0xe7/0x1d0
 20)     2732      56   scsi_request_fn+0x54/0x520
 21)     2676      12   __generic_unplug_device+0x2b/0x40
 22)     2664      24   blk_execute_rq_nowait+0x59/0x80
 23)     2640     172   blk_execute_rq+0x6b/0xb0
 24)     2468      32   scsi_execute+0xe0/0x140
 25)     2436      64   scsi_execute_req+0x152/0x160
 26)     2372      60   scsi_vpd_inquiry+0x6c/0x90
 27)     2312      44   scsi_get_vpd_page+0x112/0x160
 28)     2268      52   sd_revalidate_disk+0x1df/0x320
 29)     2216      92   rescan_partitions+0x98/0x330
 30)     2124      52   __blkdev_get+0x309/0x350
 31)     2072       8   blkdev_get+0xf/0x20
 32)     2064      44   register_disk+0xff/0x120
 33)     2020      36   add_disk+0x6e/0xb0
 34)     1984      44   sd_probe_async+0xfb/0x1d0
 35)     1940      44   __async_schedule+0xf4/0x1b0
 36)     1896       8   async_schedule+0x12/0x20
 37)     1888      60   sd_probe+0x305/0x360
 38)     1828      44   really_probe+0x63/0x170
 39)     1784      36   driver_probe_device+0x5d/0x60
 40)     1748      16   __device_attach+0x49/0x50
 41)     1732      32   bus_for_each_drv+0x5b/0x80
 42)     1700      24   device_attach+0x6b/0x70
 43)     1676      16   bus_attach_device+0x47/0x60
 44)     1660      76   device_add+0x33d/0x400
 45)     1584      52   scsi_sysfs_add_sdev+0x6a/0x2c0
 46)     1532     108   scsi_add_lun+0x44b/0x460
 47)     1424     116   scsi_probe_and_add_lun+0x182/0x4e0
 48)     1308      36   __scsi_add_device+0xd9/0xe0
 49)     1272      44   ata_scsi_scan_host+0x10b/0x190
 50)     1228      24   async_port_probe+0x96/0xd0
 51)     1204      44   __async_schedule+0xf4/0x1b0
 52)     1160       8   async_schedule+0x12/0x20
 53)     1152      48   ata_host_register+0x171/0x1d0
 54)     1104      60   ata_pci_sff_activate_host+0xf3/0x230
 55)     1044      44   ata_pci_sff_init_one+0xea/0x100
 56)     1000      48   amd_init_one+0xb2/0x190
 57)      952       8   local_pci_probe+0x13/0x20
 58)      944      32   pci_device_probe+0x68/0x90
 59)      912      44   really_probe+0x63/0x170
 60)      868      36   driver_probe_device+0x5d/0x60
 61)      832      20   __driver_attach+0x89/0xa0
 62)      812      32   bus_for_each_dev+0x5b/0x80
 63)      780      12   driver_attach+0x1e/0x20
 64)      768      72   bus_add_driver+0x14b/0x2d0
 65)      696      36   driver_register+0x6e/0x150
 66)      660      20   __pci_register_driver+0x53/0xc0
 67)      640       8   amd_init+0x14/0x16
 68)      632     572   do_one_initcall+0x2b/0x1d0
 69)       60      12   do_basic_setup+0x56/0x6a
 70)       48      20   kernel_init+0x84/0xce
 71)       28      28   kernel_thread_helper+0x7/0x10

There's a lot of fat functions on that stack trace, but
the largest of all is do_one_initcall(). This is due to
the boot trace entry variables being on the stack.

Fixing this is relatively easy, initcalls are fundamentally
serialized, so we can move the local variables to file scope.

Note that this large stack footprint was present for a
couple of months already - what pushed my system over
the edge was the addition of kmemleak to the call-chain:

  6)     3328      36   allocate_slab+0xb1/0x100
  7)     3292      36   new_slab+0x1c/0x160
  8)     3256      36   __slab_alloc+0x133/0x2b0
  9)     3220       4   kmem_cache_alloc+0x1bb/0x1d0
 10)     3216     108   create_object+0x28/0x250
 11)     3108      40   kmemleak_alloc+0x81/0xc0
 12)     3068      24   kmem_cache_alloc+0x162/0x1d0
 13)     3044      52   scsi_pool_alloc_command+0x29/0x70

This pushes the total to ~3800 bytes, only a tiny bit
more was needed to corrupt the on-kernel-stack thread_info.

The fix reduces the stack footprint from 572 bytes
to 28 bytes.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>