Comment 4 for bug 1802021

Joe, is your kernel different than the one Gavin Guo built for us here? https://launchpad.net/~mimi0213kimo/+archive/ubuntu/sf00204509-rcu-backport

We have enabled extra debugging and given that kernel to our internal customer who attempting to repro. Since the repro takes a very long time it is difficult to decide when the fix is working or not.

Paul McKenney upstream has submitted a pull request for this patch (and others) to go into 4.21. Getting some "burn in" time upstream hasn't really started in earnest yet, but there is no negative discussion about the PR, and I am tempted to get this into the regular based on Paul's comment: "Lock srcu_data structure in srcu_gp_start(), fixing a an extremely rare but also extremely embarrassing concurrency bug, courtesy of Dennis Krein."