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    SubjectRe: [PATCH] mce: fix RCU lockdep from mce_log()
    On Sat, Nov 06, 2010 at 07:53:50PM +0100, Andi Kleen wrote:
    > On Fri, Nov 05, 2010 at 06:44:59PM -0300, Davidlohr Bueso wrote:
    > > Hi,
    > >
    > > Please review this patch, I am not very familiar with MCE/RCU so I'm not sure that this is the correct fix (otherwise consider it a bug report :)).
    > > This does "fix" the message though and I can use MCE normally.
    > The patch is certainly not correct. The variable needs to be read
    > independently of the mutex.

    This code is simply checking the value of the pointer, and therefore
    need not protect any actual dereferences. So why not replace the
    rcu_dereference_check_mce() with rcu_access_pointer()? If this is
    OK, please see the patch below.

    BTW, assigning the value returned by rcu_access_pointer() into a
    variable often indicates a bug. ;-)

    Thanx, Paul

    Signed-off-by: Paul E. McKenney <>

    diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
    index 7a35b72..4d29d50 100644
    --- a/arch/x86/kernel/cpu/mcheck/mce.c
    +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    @@ -1625,7 +1625,7 @@ out:
    static unsigned int mce_poll(struct file *file, poll_table *wait)
    poll_wait(file, &mce_wait, wait);
    - if (rcu_dereference_check_mce(
    + if (rcu_access_pointer(
    if (!mce_apei_read_done && apei_check_mce())

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      Last update: 2010-11-07 14:43    [W:0.021 / U:20.300 seconds]
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