On Fri, Oct 13, 2017 at 06:33:52PM +0200, Greg KH wrote: > On Fri, Oct 13, 2017 at 09:25:43AM -0700, Paul E. McKenney wrote: > > On Fri, Oct 13, 2017 at 11:52:45AM +0200, Greg KH wrote: > > > On Thu, Oct 12, 2017 at 04:09:28PM -0700, Paul E. McKenney wrote: > > > > A number of architecture invoke rcu_irq_enter() on exception entry in > > > > order to allow RCU read-side critical sections in the exception handler > > > > when the exception is from an idle or nohz_full CPU. This works, at > > > > least unless the exception happens in an NMI handler. In that case, > > > > rcu_nmi_enter() would already have exited the extended quiescent state, > > > > which would mean that rcu_irq_enter() would (incorrectly) cause RCU > > > > to think that it is again in an extended quiescent state. This will > > > > in turn result in lockdep splats in response to later RCU read-side > > > > critical sections. > > > > > > > > This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to > > > > take no action if there is an rcu_nmi_enter() in effect, thus avoiding > > > > the unscheduled return to RCU quiescent state. This in turn should > > > > make the kernel safe for on-demand RCU voyeurism. > > > > > > > > Link: http://lkml.kernel.org/r/20170922211022.GA18084@xxxxxxxxxxxxxxxxxx > > > > > > > > Cc: stable@xxxxxxxxxxxxxxx # 4.2.x > > > > Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") > > > > Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx> > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > > > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > > > > > > This does not apply to the 4.4-stable tree, was this the correct patch I > > > should be using for that tree? > > > > Hmmm... Idiot here backported to v4.4 in Linus's tree, which of > > course might not work... But it applies to v4.4.92 of -stable: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git > > > > Am I still applying it in the wrong place? > > Ugh, no, you are doing the right thing. I don't know what failed on my > end, that's what I get for trying to deal with RCU early in the morning > :) Believe me, I know that feeling very well! ;-) Thanx, Paul > I'll go apply this now, sorry for the noise, and thanks for checking and > the backport. > > greg k-h >