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    SubjectRe: tracing ring_buffer_resize oops.
    On 05/24/2012 04:40 PM, Steven Rostedt wrote:
    > On Thu, 2012-05-24 at 13:22 -0400, Dave Jones wrote:
    > I found a clue!
    >> [ 1013.243754] BUG: unable to handle kernel NULL pointer dereference at 0000000000000002
    >> [ 1013.272665] IP: [<ffff880145cc0000>] 0xffff880145cbffff
    >> [ 1013.285186] PGD 1401b2067 PUD 14324c067 PMD 0
    >> [ 1013.298832] Oops: 0010 [#1] PREEMPT SMP
    >> [ 1013.310600] CPU 2
    >> [ 1013.317904] Modules linked in: ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables crc32c_intel ghash_clmulni_intel microcode usb_debug serio_raw pcspkr iTCO_wdt i2c_i801 iTCO_vendor_support e1000e nfsd nfs_acl auth_rpcgss lockd sunrpc i915 video i2c_algo_bit drm_kms_helper drm i2c_core [last unloaded: scsi_wait_scan]
    >> [ 1013.401848]
    >> [ 1013.407399] Pid: 112, comm: kworker/2:1 Not tainted 3.4.0+ #30
    >> [ 1013.437943] RIP: 8eb8:[<ffff88014630a000>] [<ffff88014630a000>] 0xffff880146309fff
    > RIP is always near the GS segment. As GS points to the per_cpu area, we
    > may somehow be getting our GS screwed up. I'm not sure why that would
    > affect the RIP. Maybe stacks are not being processed properly somewhere?
    > It's strange because I can either trigger it on the first try, or it
    > never triggers at all??

    Much more fundamentally, RIP should never leave the range [-2G, 0).
    What is happening here is almost certainly that we jump through
    something which isn't a function pointer.

    The other thing worth noting is that the code segment is not the
    standard Linux code segment, not even close; it *also* doesn't look like
    the typical Xen code segment. This makes be believe that we did an IRET
    with the stack pointer set to something other than a valid interrupt
    stack frame. Specifically, note that the value of R12 is the same
    value; R12 is a preserved register and may have been pushed onto the
    stack by something that wants to save it.

    Waitaminute... this isn't related to your using R12 to save a pointer to
    something, is it?

    > [ 1013.459871] RSP: ffffffff8165e919:ffff88014780f408 EFLAGS: 00010046


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      Last update: 2012-05-25 02:21    [W:0.022 / U:8.896 seconds]
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