[Crash-utility] cannot load slab info from 3.11 dump because of invalid pointer in kmem_cache

[Anatol Pomozov]

Hi,

Not clear if it is a 3.11 issue or just general memory corruption. But
I clearly cannot load slab information from any of my 3.11 dumps. Slab
info contain incorrect pointer and "crash" just drops all slab
information.

Crash expects that kmem_cache.array contains either valid pointer or
NULL. And most slabs indeed have valid data. But there is also struct
like below and crash says:

crash: invalid kernel virtual address: 28  type: "array cache limit"

Dave, do you have any pointer what it can be?

If this is a memory corruption in one of the slab, would it be better
if "crash" just skipped this slab (or marked it as 'fail to load') and
show info for the rest of caches?

struct kmem_cache {
  batchcount = 16,
  limit = 32,
  shared = 8,
  size = 64,
  reciprocal_buffer_size = 67108864,
  flags = 10240,
  num = 59,
  gfporder = 0,
  allocflags = 0,
  colour = 0,
  colour_off = 64,
  slabp_cache = 0x0 <irq_stack_union>,
  slab_size = 320,
  ctor = 0x0 <irq_stack_union>,
  name = 0xffff88065786ea60 "fib6_nodes",
  list = {
    next = 0xffff880654d9d618,
    prev = 0xffff880c50f24f98
  },
  refcount = 1,
  object_size = 48,
  align = 64,
  num_active = 5,
  num_allocations = 32,
  high_mark = 20,
  grown = 1,
  reaped = 0,
  errors = 0,
  max_freeable = 0,
  node_allocs = 0,
  node_frees = 0,
  node_overflow = 0,
  allochit = {
    counter = 3
  },
  allocmiss = {
    counter = 2
  },
  freehit = {
    counter = 0
  },
  freemiss = {
    counter = 0
  },
  obj_offset = 0,
  memcg_params = 0x0 <irq_stack_union>,
  node = 0xffff880654da37b0,
  array = {0xffff880654d68e00, 0xffff880654d69e00, 0xffff880654d6ae00,
0xffff880654da4e00, 0xffff880654da5e00, 0xffff880654da6e00,
0xffff880c50faee00, 0xffff880c50fb2e00, 0xffff880c51722e00,
0xffff880c51723e00, 0xffff880c4e83de00, 0xffff880c5172be00,
0xffff880654da7e00, 0xffff880654da8e00, 0xffff880654da9e00,
0xffff880654daae00, 0xffff880654dabe00, 0xffff880654dade00,
0xffff880c4e83ee00, 0xffff880c4e83fe00, 0xffff880c5172ae00,
0xffff880c51724e00, 0xffff880c50e69e00, 0xffff880c510b3e00,
0xffff880654e07a80, 0xffff880c4e903940, 0x24 <irq_stack_union+36>,
0xc000100003c1b, 0xe7e0 <ftrace_stack+2016>, 0x19
<irq_stack_union+25>, 0x1000200003c2a, 0x54670, 0x1fe
<irq_stack_union+510>, 0xc000100003c48, 0xe8d7 <ftrace_stack+2263>,
0xf <irq_stack_union+15>, 0xc000100003c57, 0xe8c0 <ftrace_stack+2240>,
0x17 <irq_stack_union+23>, 0x1000200003c66, 0x54870, 0x2a3
<irq_stack_union+675>, 0xc000100003c79, 0xe8a0 <ftrace_stack+2208>,
0x13 <irq_stack_union+19>, 0x19000100003c88, 0x0 <irq_stack_union>,
0x28 <irq_stack_union+40>, 0x1000200003c99, 0x54b20, 0x917
<irq_stack_union+2327>, 0xc000100003cab, 0xe8f0 <ftrace_stack+2288>,
0x16 <irq_stack_union+22>, 0x1000200003cba, 0x55440, 0x30
<irq_stack_union+48>, 0x1000200003cce, 0x55470, 0x2bb
<irq_stack_union+699>, 0xc000100003ce5, 0xe930 <ftrace_stack+2352>,
0x17 <irq_stack_union+23>, 0x1000200003cf4, 0x55730, 0x38
<irq_stack_union+56>, 0x1000200003d0a, 0x55770}
}



"crash" fails on array[26] that has value "0x24 <irq_stack_union+36>"