On Thu, 10 Oct 2013 11:10:35 -0700 Linus Torvalds <torva...@linux-foundation.org> wrote: .. now we can free all the percpu data and kill the CPU .. > > without any locking anywhere - not stop-machine, not anything. If > somebody is doing a "for_each_cpu()" (under just a regular > rcu_read_lock()) and they see the bit set while it's going down, who > cares? The CPU is still there, the data is accessible..
The problem is that rcu_read_lock() requires preemption disabled unless you are using the preemptable rcu tree version. There's always srcu_read_lock() but that's not so free. It's basically the same as what Peter is doing. There's places in the kernel that does for_each_cpu() that I'm sure you don't want to disable preemption for. Especially when you start having 4096 CPU machines! -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/