On Thu, Jun 06, 2019 at 10:19:43AM -0400, Alan Stern wrote: > On Thu, 6 Jun 2019, Andrea Parri wrote: > > > This seems a sensible change to me: looking forward to seeing a patch, > > on top of -rcu/dev, for further review and testing! > > > > We could also add (to LKMM) the barrier() for rcu_read_{lock,unlock}() > > discussed in this thread (maybe once the RCU code and the informal doc > > will have settled in such direction). > > Yes. Also for SRCU. That point had not escaped me. And it does seem pretty settled. There are quite a few examples where there are normal accesses at either end of the RCU read-side critical sections, for example, the one in the requirements diffs below. For SRCU, srcu_read_lock() and srcu_read_unlock() have implied compiler barriers since 2006. ;-) Thanx, Paul ------------------------------------------------------------------------ diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 5a9238a2883c..080b39cc1dbb 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -2129,6 +2129,8 @@ Some of the relevant points of interest are as follows: <li> <a href="#Hotplug CPU">Hotplug CPU</a>. <li> <a href="#Scheduler and RCU">Scheduler and RCU</a>. <li> <a href="#Tracing and RCU">Tracing and RCU</a>. +<li> <a href="#Accesses to User Mamory and RCU">

+Accesses to User Mamory and RCU</a>.

<li> <a href="#Energy Efficiency">Energy Efficiency</a>. <li> <a href="#Scheduling-Clock Interrupts and RCU"> Scheduling-Clock Interrupts and RCU</a>. @@ -2521,6 +2523,75 @@ cannot be used. The tracing folks both located the requirement and provided the needed fix, so this surprise requirement was relatively painless. +<h3><a name="Accesses to User Mamory and RCU">

+Accesses to User Mamory and RCU</a></h3>