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    SubjectRe: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread
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    On Wed, 2011-02-23 at 11:34 -0600, Christoph Lameter wrote:

    > > > True, but we could also argue that the multiple checks for being preempt
    > > > can also be an issue.
    > >
    > > At least on x86 preemption don't actually need to be disabled: selection
    > > of the right per-cpu memory location is done atomically with the rest of
    > > the instruction by the segment selector.
    >
    > Right.

    But a test still needs to be made. Because three access of this_cpu_*()
    that gets preempted and scheduled on another CPU can access a different
    CPU var for each access. This does not matter how atomic the
    this_cpu_*() code is.

    IOW, the use of this_cpu_*() without preemption disabled is 99% of the
    time a bug.

    -- Steve




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