Hi everybody, I am trying to figure out the race condition that commit 7cccd8 fixes. The commit disables preemption in between the retrieval of the per-cpu slab and the subsequent read of the slab's tid. According to the commit message, this change helps avoid allocating from the wrong node in slab_alloc. But try as I might, I can't see how allocating from the wrong node, let alone the wrong cpu, could ever happen with or without preemption. Isn't the globally-unique per-cpu tid the mechanism that's supposed to guard against allocating from the wrong cpu or node? In what way does this mechanism fail in slab_alloc_node, and how does disabling preemption during the retrieval of the tid mitigate this failure? Would really appreciate if somebody took the time to explain this to a newbie like me.
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