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    SubjectRe: [2.6.30-rc1] RCU detected CPU 1 stall
    On Mon, 13 Apr 2009, Tetsuo Handa wrote:
    > Paul E. McKenney wrote:
    > > Is this reproducible?
    > Not always, but it is reproducible.
    >
    > Al Viro wrote:
    > > I'd really love to see results of repeated alt-sysrq-p/alt-sysrq-l, just
    > > to see where was it actually spinning.
    > Below is sysrq message.
    > Maybe something related to khelper's current->mm == NULL warning problem.

    Maybe, up to a point, and I'll post separately on those warnings.

    > Full log is at http://I-love.SAKURA.ne.jp/tmp/dmesg-2.6.30-rc1-200904130930.txt .
    >
    > [ 47.412519] SysRq : Show Regs
    > [ 47.413986]
    > [ 47.414584] Pid: 3655, comm: khelper Tainted: G W (2.6.30-rc1 #1) VMware Virtual Platform
    > [ 47.415804] EIP: 0060:[<c0379c3d>] EFLAGS: 00000293 CPU: 0
    > [ 47.415804] EIP is at __get_user_4+0x11/0x17
    > [ 47.415804] EAX: f7150003 EBX: f7150000 ECX: 00000000 EDX: f6744000
    > [ 47.415804] ESI: 000007b8 EDI: 7fffffff EBP: f6744f20 ESP: f6744f10
    > [ 47.415804] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
    > [ 47.415804] CR0: 8005003b CR2: f7150000 CR3: 3599a000 CR4: 000006d0
    > [ 47.415804] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
    > [ 47.415804] DR6: ffff0ff0 DR7: 00000400
    > [ 47.415804] Call Trace:
    > [ 47.415804] [<c0225f4e>] ? count+0x3e/0xb0
    > [ 47.415804] [<c0228581>] do_execve+0x621/0x890
    > [ 47.415804] [<c022bd8b>] ? getname+0x6b/0xa0
    > [ 47.415804] [<c010237e>] sys_execve+0x5e/0xb0
    > [ 47.415804] [<c0103d19>] syscall_call+0x7/0xb
    > [ 47.415804] [<c010aee4>] ? kernel_execve+0x24/0x30
    > [ 47.415804] [<c0172b6f>] ? ____call_usermodehelper+0xff/0x170
    > [ 47.415804] [<c0172a70>] ? ____call_usermodehelper+0x0/0x170
    > [ 47.415804] [<c0104707>] ? kernel_thread_helper+0x7/0x10

    I'm now thinking that this really is hitting in count(), despite
    the ? on that in the backtrace, and is entirely unrelated to the
    recent check_unsafe_exec() changes. Stuck in a loop scanning the
    the kernelspace exec args without an mm.

    But my compiler on your config gives quite different function
    sizes: please would you post to the list or send me privately
    the output of "objdump -trd fs/exec.o", so we can check that.

    Thanks,
    Hugh


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