On Wed, May 2, 2012 at 2:54 PM, Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote: > On Thu, May 03, 2012 at 07:20:15AM +1000, Benjamin Herrenschmidt wrote: >> On Wed, 2012-05-02 at 13:25 -0700, Hugh Dickins wrote: >> > Got it at last. Embarrassingly obvious. __rcu_read_lock() and >> > __rcu_read_unlock() are not safe to be using __this_cpu operations, >> > the cpu may change in between the rmw's read and write: they should >> > be using this_cpu operations (or, I put preempt_disable/enable in the >> > __rcu_read_unlock below). __this_cpus there work out fine on x86, >> > which was given good instructions to use; but not so well on PowerPC. >> > >> > I've been running successfully for an hour now with the patch below; >> > but I expect you'll want to consider the tradeoffs, and may choose a >> > different solution. >> >> Didn't Linus recently rant about these __this_cpu vs this_cpu nonsense ? >> >> I thought that was going out.. > > Linus did rant about __raw_get_cpu_var() because it cannot use the x86 > %fs segement overrides a bit more than a month ago. The __this_cpu > stuff is useful if you have preemption disabled -- avoids the extra > layer of preempt_disable(). > > Or was this a different rant?
https://lkml.org/lkml/2011/11/29/321 I think it ended up with Christoph removing the more egregious variants, but this_cpu_that and __this_cpu_the_other remaining. Hugh _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
