On Fri, 18 Jan 2013, Eric Dumazet wrote:

On Fri, 2013-01-18 at 18:40 +0000, Christoph Lameter wrote:

quoted

The fetching of the tid is the only critical thing here. If the tid is
retrieved from the right cpu then the cmpxchg will fail if any changes
occured to freelist or the page variable.

The tid can be retrieved without disabling preemption through
this_cpu_read().

Strictly speaking, this_cpu_read() _does_ disable preemption.

Yes on x86 the relocation and the fetch is just a single instruction and
therefore no preemption can occur.

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