Hello,

Here are some kmemcheck warnings I suspect to occur either in MM/kmemcheck 
subsystem, VFS, or radeon driver (the last two potentially being related).

The first one:
Sometimes, I get the following at boot when using kmemcheck and other debug 
options (.config file appended):

Freeing unused kernel memory: 628k freed
WARNING: kmemcheck: Caught 64-bit read from uninitialized memory 
(ffff8801c1e62600)
7025e6c10188ffff003adec10188ffff000110000000adde000220000000adde
 u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u
 ^

Pid: 1712, comm: udevd Tainted: G        W    3.2.0-rc6 #11 Acer Aspire 
7750G/JE70_HR
RIP: 0010:[<ffffffff8111d8e6>]  [<ffffffff8111d8e6>] kmem_cache_alloc+0x66/0x120
RSP: 0018:ffff8801c2497ce0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801c1de24e0 RCX: 000000000003eac8
RDX: 000000000003eac0 RSI: 00000000001d4b30 RDI: 00000000000000d0
RBP: ffff8801c2497d10 R08: ffff8801c249c4c8 R09: ffff8801c1e63690
R10: 0000000000000001 R11: 0000000000000000 R12: ffff8801c1e62600
R13: ffff8801c7814400 R14: 00000000000000d0 R15: ffffffff8110714b
FS:  00007f0c97f14720(0000) GS:ffff8801c7e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: ffff8801c6454448 CR3: 00000001c2452000 CR4: 00000000000406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
 [<ffffffff8110714b>] anon_vma_fork+0x7b/0x130
 [<ffffffff81075bd8>] dup_mm+0x228/0x520
 [<ffffffff81076c92>] copy_process+0xd92/0x1460
 [<ffffffff81077461>] do_fork+0xd1/0x2b0
 [<ffffffff8103d2f3>] sys_clone+0x23/0x30
 [<ffffffff817ada23>] stub_clone+0x13/0x20
 [<ffffffffffffffff>] 0xffffffffffffffff
udev[1727]: renamed network interface eth0 to eth1
udev[1717]: renamed network interface wlan0-eth0 to eth0

This log is from 3.2-rc6, I may have already reported it through bugzilla but 
I cannot check the status of this bug since it's down, so I'm reporting by 
mail.

Btw, I also have several other kmemchecks warnings, one at kernel init:

 memory used by lock dependency info: 6367 kB
 per task-struct memory footprint: 2688 bytes
------------[ cut here ]------------
WARNING: at kernel/lockdep.c:2739 lockdep_trace_alloc+0xb5/0xc0()
Hardware name: Aspire 7750G
Modules linked in:
Pid: 0, comm: swapper/0 Not tainted 3.2.0-rc6 #11
Call Trace:
 [<ffffffff810780fa>] warn_slowpath_common+0x7a/0xb0
 [<ffffffff81078145>] warn_slowpath_null+0x15/0x20
 [<ffffffff810b0315>] lockdep_trace_alloc+0xb5/0xc0
 [<ffffffff810e5f0c>] __alloc_pages_nodemask+0x8c/0x6b0
 [<ffffffff812c7f0d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
 [<ffffffff812c7f0d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
 [<ffffffff8111f954>] kmemcheck_alloc_shadow+0x54/0xf0
 [<ffffffff8111d37f>] new_slab+0x27f/0x370
 [<ffffffff817a3894>] __slab_alloc.isra.53+0x432/0x546
 [<ffffffff812c7f0d>] ? trace_hardirqs_off_thunk+0x3a/0x3c
 [<ffffffff81ea50d4>] ? debug_objects_mem_init+0x65/0x220
 [<ffffffff817ad449>] ? error_exit+0x29/0xb0
 [<ffffffff81ea50d4>] ? debug_objects_mem_init+0x65/0x220
 [<ffffffff8111d98f>] kmem_cache_alloc+0x10f/0x120
 [<ffffffff81ea50d4>] debug_objects_mem_init+0x65/0x220
 [<ffffffff81e869d1>] start_kernel+0x25a/0x2ef
 [<ffffffff81e86288>] x86_64_start_reservations+0x98/0x9c
 [<ffffffff81e86391>] x86_64_start_kernel+0x105/0x10c
---[ end trace 4eaa2a86a8e2da22 ]---
ODEBUG: 12 of 12 active objects replaced

some others in VFS:

EXT4-fs (sda2): re-mounted. Opts: commit=0
EXT4-fs (sda3): re-mounted. Opts: commit=0
WARNING: kmemcheck: Caught 64-bit read from uninitialized memory 
(ffff8801c3bdc000)
0000000000000000616c74696d65002f736f6c69642f616374696f6e732f736f
 u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u
 ^

Pid: 2423, comm: X Tainted: G        W    3.2.0-rc6 #11 Acer Aspire 
7750G/JE70_HR
RIP: 0010:[<ffffffff8111d8e6>]  [<ffffffff8111d8e6>] kmem_cache_alloc+0x66/0x120
RSP: 0018:ffff88019f88dd48  EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00000000004859b8
RDX: 00000000004859b0 RSI: 00000000001d44b0 RDI: 00000000000000d0
RBP: ffff88019f88dd78 R08: 0000000000000000 R09: 0000000002585dc0
R10: 000000000000000a R11: 0000000000000246 R12: ffff8801c3bdc000
R13: ffff8801c7804d00 R14: 00000000000000d0 R15: ffffffff81130176
FS:  00007f0c6d9848a0(0000) GS:ffff8801c7e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: ffff8801c6454448 CR3: 00000001aaa81000 CR4: 00000000000406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
 [<ffffffff81130176>] getname_flags+0x36/0x240
 [<ffffffff81134390>] user_path_at_empty+0x30/0xa0
 [<ffffffff8113440c>] user_path_at+0xc/0x10
 [<ffffffff81129555>] vfs_fstatat+0x35/0x60
 [<ffffffff811295b6>] vfs_stat+0x16/0x20
 [<ffffffff811296c5>] sys_newstat+0x15/0x30
 [<ffffffff817ad73b>] system_call_fastpath+0x16/0x1b
 [<ffffffffffffffff>] 0xffffffffffffffff
eth0: deauthenticating from 9a:37:17:7c:4a:2c by local choice (reason=3)

and finally some in radeon driver:

WARNING: kmemcheck: Caught 16-bit read from uninitialized memory 
(ffff8801c3ec4822)
ffff00ffffffffbf7fff00dbefc7feffffff00fff7ffffffffff00fcffffffff
 i i u u u u u u u u u u u u u u u u u u u u u u u u u u u u u u
     ^

Pid: 2423, comm: X Tainted: G        W    3.2.0-rc6 #11 Acer Aspire 
7750G/JE70_HR
RIP: 0010:[<ffffffff8135bc05>]  [<ffffffff8135bc05>] drm_fb_helper_setcmap+0x125/0x3c0
RSP: 0018:ffff8801aaac3918  EFLAGS: 00010246
RAX: 0000000000000011 RBX: 0000000000000011 RCX: 0000000000000000
RDX: ffff8801c3ec4800 RSI: 0000000000ff0000 RDI: ffff8801c3ea33a0
RBP: ffff8801aaac39d8 R08: 0000000000000000 R09: 0000000000000011
R10: 000000000000ff00 R11: 000000000000ff00 R12: ffff8801c3ea3000
R13: ffff8801c3ec4400 R14: ffff8801c3ec4a24 R15: ffff8801c3ec44b8
FS:  00007f0c6d9848a0(0000) GS:ffff8801c7e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff8801c6454448 CR3: 00000001aaa81000 CR4: 00000000000406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff4ff0 DR7: 0000000000000400
 [<ffffffff812f8be5>] fb_set_cmap+0x65/0x140
 [<ffffffff812f667d>] fb_set_var+0x19d/0x3b0
 [<ffffffff81300874>] fbcon_blank+0x1e4/0x2d0
 [<ffffffff8135405b>] do_unblank_screen+0xab/0x1d0
 [<ffffffff81349af4>] complete_change_console+0x64/0xf0
 [<ffffffff8134b5e5>] vt_ioctl+0x1a65/0x2070
 [<ffffffff81340ddc>] tty_ioctl+0x28c/0xc50
 [<ffffffff81136da6>] do_vfs_ioctl+0x96/0x570
 [<ffffffff811372ca>] sys_ioctl+0x4a/0x80
 [<ffffffff817ad73b>] system_call_fastpath+0x16/0x1b
 [<ffffffffffffffff>] 0xffffffffffffffff
Freezing user space processes ... (elapsed 0.07 seconds) done.

but this one may be also a VFS warning.

For information, I'm using slub allocator, on a Core i7 laptop in 64bits mode, 
6GB RAM (Acer Aspire 7750G to be precise), on Slackware64 13.37.
Appended: .config file for this kernel.

CC