lkml.org 
[lkml]   [2019]   [Jun]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: rcu_read_lock lost its compiler barrier
On Sat, 8 Jun 2019, Paul E. McKenney wrote:

> 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>
---------------------^

Are these issues especially notable for female programmers? :-)

Alan

\
 
 \ /
  Last update: 2019-06-08 17:56    [W:0.088 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site