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    Subject3.6rc6 slab corruption.
    I was chasing a networking bug, and had trinity reduced to just making read & setsockopt calls,
    and let that run overnight. I woke up to 800mb of traces from a different bug..

    The traces look mostly like this..


    =============================================================================
    BUG kmalloc-64 (Not tainted): Redzone overwritten
    -----------------------------------------------------------------------------

    INFO: 0xffff88001f4b4970-0xffff88001f4b4977. First byte 0xbb instead of 0xcc
    INFO: Allocated in u32_array_read+0xd1/0x110 age=0 cpu=6 pid=32767
    __slab_alloc+0x516/0x5a5
    __kmalloc+0x213/0x2c0
    u32_array_read+0xd1/0x110
    vfs_read+0xac/0x180
    sys_read+0x4d/0x90
    system_call_fastpath+0x1a/0x1f
    INFO: Freed in u32_array_read+0x99/0x110 age=0 cpu=0 pid=32749
    __slab_free+0x3f/0x3bf
    kfree+0x2d5/0x310
    u32_array_read+0x99/0x110
    vfs_read+0xac/0x180
    sys_read+0x4d/0x90
    system_call_fastpath+0x1a/0x1f
    INFO: Slab 0xffffea00007d2d00 objects=41 used=14 fp=0xffff88001f4b7410 flags=0x10000000004081
    INFO: Object 0xffff88001f4b4930 @offset=2352 fp=0xffff88001f4b7410

    Bytes b4 ffff88001f4b4920: 1b 20 1c 00 01 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a . ......ZZZZZZZZ
    Object ffff88001f4b4930: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
    Object ffff88001f4b4940: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
    Object ffff88001f4b4950: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
    Object ffff88001f4b4960: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
    Redzone ffff88001f4b4970: bb bb bb bb bb bb bb bb ........
    Padding ffff88001f4b4ab0: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
    Pid: 32756, comm: trinity-child52 Not tainted 3.6.0-rc6+ #44
    Call Trace:
    [<ffffffff811c10ad>] ? print_section+0x3d/0x40
    [<ffffffff811c23fe>] print_trailer+0xfe/0x160
    [<ffffffff811c2592>] check_bytes_and_report+0xe2/0x120
    [<ffffffff81023b79>] ? native_sched_clock+0x19/0x80
    [<ffffffff811c2b5b>] check_object+0x18b/0x250
    [<ffffffff8169b7d7>] free_debug_processing+0xc0/0x1fd
    [<ffffffff812d2e29>] ? u32_array_read+0x99/0x110
    [<ffffffff8169ba5c>] __slab_free+0x3f/0x3bf
    [<ffffffff81365a1c>] ? debug_check_no_obj_freed+0x16c/0x210
    [<ffffffff810db04f>] ? lock_release_holdtime.part.26+0xf/0x180
    [<ffffffff812d2e29>] ? u32_array_read+0x99/0x110
    [<ffffffff811c5725>] kfree+0x2d5/0x310
    [<ffffffff812d2e29>] u32_array_read+0x99/0x110
    [<ffffffff811df88c>] vfs_read+0xac/0x180
    [<ffffffff811df9ad>] sys_read+0x4d/0x90
    [<ffffffff816aea2d>] system_call_fastpath+0x1a/0x1f
    FIX kmalloc-64: Restoring 0xffff88001f4b4970-0xffff88001f4b4977=0xcc
    =============================================================================

    Which looks like we read some file (probably something in sysfs/procfs) that corrupted some internal state.
    Any ideas on what I could do to narrow this down ?

    The full traces are at http://www.codemonkey.org.uk/junk/slab-corrupt.txt
    They vary a little later, but it looks like it's probably all the same problem to me.
    Sometimes it flip-flops between "First byte 0xbb instead of 0xcc" and "First byte 0xcc instead of 0xbb"


    The one outlier being this weird message..

    Sep 18 02:00:13 bitcrush kernel: [36617.487681] hrtimer: interrupt took 242337 ns

    Which is weird, but probably unrelated.

    Dave



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