On Tue, Sep 27, 2016 at 04:22:20PM +0200, Frederic Weisbecker wrote: > The RCU context tracking doesn't take care of callbacks. It's only there > to tell the RCU core whether the CPU runs code that may or may not run > RCU read side critical sections. This is assumed by "kernel may use RCU, > userspace can't". Userspace never can use the kernels RCU in any case. What you mean to say is that userspace is treated like an idle CPU in that the CPU will no longer be part of the RCU quescent state machine. The transition to userspace (as per context tracking) must ensure that CPUs RCU state is 'complete', just like our transition to idle (mostly) does. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>