[PATCH] mm/slub: Switch slub_debug kernel option to early_param to avoid boot panic

[Andreas Herrmann <andreas.herrmann@calxeda.com>]

When I've used slub_debug kernel option (e.g.
"slub_debug=,skbuff_fclone_cache" or similar) on a debug session I've
seen a panic like:

  Highbank #setenv bootargs console=ttyAMA0 root=/dev/sda2 kgdboc.kgdboc=ttyAMA0,115200 slub_debug=,kmalloc-4096 earlyprintk=ttyAMA0
  ...
  Unable to handle kernel NULL pointer dereference at virtual address 00000000
  pgd = c0004000
  [00000000] *pgd=00000000
  Internal error: Oops: 5 [#1] SMP ARM
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper Tainted: G        W    3.12.0-00048-gbe408cd #314
  task: c0898360 ti: c088a000 task.ti: c088a000
  PC is at strncmp+0x1c/0x84
  LR is at kmem_cache_flags.isra.46.part.47+0x44/0x60
  pc : [<c02c6da0>]    lr : [<c0110a3c>]    psr: 200001d3
  sp : c088bea8  ip : c088beb8  fp : c088beb4
  r10: 00000000  r9 : 413fc090  r8 : 00000001
  r7 : 00000000  r6 : c2984a08  r5 : c0966e78  r4 : 00000000
  r3 : 0000006b  r2 : 0000000c  r1 : 00000000  r0 : c2984a08
  Flags: nzCv  IRQs off  FIQs off  Mode SVC_32  ISA ARM  Segment kernel
  Control: 10c5387d  Table: 0000404a  DAC: 00000015
  Process swapper (pid: 0, stack limit = 0xc088a248)
  Stack: (0xc088bea8 to 0xc088c000)
  bea0:                   c088bed4 c088beb8 c0110a3c c02c6d90 c0966e78 00000040
  bec0: ef001f00 00000040 c088bf14 c088bed8 c0112070 c0110a04 00000005 c010fac8
  bee0: c088bf5c c088bef0 c010fac8 ef001f00 00000040 00000000 00000040 00000001
  bf00: 413fc090 00000000 c088bf34 c088bf18 c0839190 c0112040 00000000 ef001f00
  bf20: 00000000 00000000 c088bf54 c088bf38 c0839200 c083914c 00000006 c0961c4c
  bf40: c0961c28 00000000 c088bf7c c088bf58 c08392ac c08391c0 c08a2ed8 c0966e78
  bf60: c086b874 c08a3f50 c0961c28 00000001 c088bfb4 c088bf80 c083b258 c0839248
  bf80: 2f800000 0f000000 c08935b4 ffffffff c08cd400 ffffffff c08cd400 c0868408
  bfa0: c29849c0 00000000 c088bff4 c088bfb8 c0824974 c083b1e4 ffffffff ffffffff
  bfc0: c08245c0 00000000 00000000 c0868408 00000000 10c5387d c0892bcc c0868404
  bfe0: c0899440 0000406a 00000000 c088bff8 00008074 c0824824 00000000 00000000
  [<c02c6da0>] (strncmp+0x1c/0x84) from [<c0110a3c>] (kmem_cache_flags.isra.46.part.47+0x44/0x60)
  [<c0110a3c>] (kmem_cache_flags.isra.46.part.47+0x44/0x60) from [<c0112070>] (__kmem_cache_create+0x3c/0x410)
  [<c0112070>] (__kmem_cache_create+0x3c/0x410) from [<c0839190>] (create_boot_cache+0x50/0x74)
  [<c0839190>] (create_boot_cache+0x50/0x74) from [<c0839200>] (create_kmalloc_cache+0x4c/0x88)
  [<c0839200>] (create_kmalloc_cache+0x4c/0x88) from [<c08392ac>] (create_kmalloc_caches+0x70/0x114)
  [<c08392ac>] (create_kmalloc_caches+0x70/0x114) from [<c083b258>] (kmem_cache_init+0x80/0xe0)
  [<c083b258>] (kmem_cache_init+0x80/0xe0) from [<c0824974>] (start_kernel+0x15c/0x318)
  [<c0824974>] (start_kernel+0x15c/0x318) from [<00008074>] (0x8074)
  Code: e3520000 01a00002 089da800 e5d03000 (e5d1c000)
  ---[ end trace 1b75b31a2719ed1d ]---
  Kernel panic - not syncing: Fatal exception

Problem is that slub_debug option is not parsed before
create_boot_cache is called. Solve this by changing slub_debug to
early_param.

Kernels 3.11, 3.10 are also affected.
I am not sure about older kernels.

Cc: stable@vger.kernel.org    #3.10 and 3.11
Signed-off-by: Andreas Herrmann <andreas.herrmann@calxeda.com>
---
 mm/slub.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Patch is against v3.12-48-gbe408cd.

Regards,
Andreas

diff --git a/mm/slub.c b/mm/slub.c
index c3eb3d3..596c58a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1205,10 +1205,9 @@ check_slabs:
 	if (*str == ',')
 		slub_debug_slabs = str + 1;
 out:
-	return 1;
+	return 0;
 }
-
-__setup("slub_debug", setup_slub_debug);
+early_param("slub_debug", setup_slub_debug);
 
 static unsigned long kmem_cache_flags(unsigned long object_size,
 	unsigned long flags, const char *name,
-- 
1.7.9.5

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