+SLUB Debug output
+-----------------
+
+Here is a sample of slub debug output:
+
+*** SLUB kmalloc-8: Redzone Active@0xc90f6d20 slab 0xc528c530 offset=3360 flags=0x400000c3 inuse=61 freelist=0xc90f6d58
+ Bytes b4 0xc90f6d10: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
+ Object 0xc90f6d20: 31 30 31 39 2e 30 30 35 1019.005
+ Redzone 0xc90f6d28: 00 cc cc cc .
+FreePointer 0xc90f6d2c -> 0xc90f6d58
+Last alloc: get_modalias+0x61/0xf5 jiffies_ago=53 cpu=1 pid=554
+Filler 0xc90f6d50: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
+ [<c010523d>] dump_trace+0x63/0x1eb
+ [<c01053df>] show_trace_log_lvl+0x1a/0x2f
+ [<c010601d>] show_trace+0x12/0x14
+ [<c0106035>] dump_stack+0x16/0x18
+ [<c017e0fa>] object_err+0x143/0x14b
+ [<c017e2cc>] check_object+0x66/0x234
+ [<c017eb43>] __slab_free+0x239/0x384
+ [<c017f446>] kfree+0xa6/0xc6
+ [<c02e2335>] get_modalias+0xb9/0xf5
+ [<c02e23b7>] dmi_dev_uevent+0x27/0x3c
+ [<c027866a>] dev_uevent+0x1ad/0x1da
+ [<c0205024>] kobject_uevent_env+0x20a/0x45b
+ [<c020527f>] kobject_uevent+0xa/0xf
+ [<c02779f1>] store_uevent+0x4f/0x58
+ [<c027758e>] dev_attr_store+0x29/0x2f
+ [<c01bec4f>] sysfs_write_file+0x16e/0x19c
+ [<c0183ba7>] vfs_write+0xd1/0x15a
+ [<c01841d7>] sys_write+0x3d/0x72
+ [<c0104112>] sysenter_past_esp+0x5f/0x99
+ [<b7f7b410>] 0xb7f7b410
+ =======================
+@@@ SLUB kmalloc-8: Restoring redzone (0xcc) from 0xc90f6d28-0xc90f6d2b
+
+
+
+If SLUB encounters a corrupted object then it will perform the following
+actions:
+
+1. Isolation and report of the issue
+
+This will be a message in the system log starting with
+
+*** SLUB <slab cache affected>: <What went wrong>@<object address>
+offset=<offset of object into slab> flags=<slabflags>
+inuse=<objects in use in this slab> freelist=<first free object in slab>
+
+2. Report on how the problem was dealt with in order to ensure the continued
+operation of the system.
+
+These are messages in the system log beginning with
+
+@@@ SLUB <slab cache affected>: <corrective action taken>
+
+
+In the above sample SLUB found that the Redzone of an active object has
+been overwritten. Here a string of 8 characters was written into a slab that
+has the length of 8 characters. However, a 8 character string needs a
+terminating 0. That zero has overwritten the first byte of the Redzone field.
+After reporting the details of the issue encountered the @@@ SLUB message
+tell us that SLUB has restored the redzone to its proper value and then
+system operations continue.
+
+Various types of lines can follow the @@@ SLUB line:
+
+Bytes b4 <address> : <bytes>
+ Show a few bytes before the object where the problem was detected.
+ Can be useful if the corruption does not stop with the start of the
+ object.
+
+Object <address> : <bytes>
+ The bytes of the object. If the object is inactive then the bytes
+ typically contain poisoning values. Any non-poison value shows a
+ corruption by a write after free.
+
+Redzone <address> : <bytes>
+ The redzone following the object. The redzone is used to detect
+ writes after the object. All bytes should always have the same
+ value. If there is any deviation then it is due to a write after
+ the object boundary.
+
+Freepointer
+ The pointer to the next free object in the slab. May become
+ corrupted if overwriting continues after the red zone.
+
+Last alloc:
+Last free:
+ Shows the address from which the object was allocated/freed last.
+ We note the pid, the time and the CPU that did so. This is usually
+ the most useful information to figure out where things went wrong.
+ Here get_modalias() did an kmalloc(8) instead of a kmalloc(9).
+
+Filler <address> : <bytes>
+ Unused data to fill up the space in order to get the next object
+ properly aligned. In the debug case we make sure that there are
+ at least 4 bytes of filler. This allow for the detection of writes
+ before the object.
+
+Following the filler will be a stackdump. That stackdump describes the
+location where the error was detected. The cause of the corruption is more
+likely to be found by looking at the information about the last alloc / free.
+
+Christoph Lameter, <clameter@sgi.com>, May 23, 2007