Re: [PATCH tip/core/rcu 02/19] rcu: Defer reporting RCU-preempt quiescent states when disabled

["Paul E. McKenney" <paulmck@linux.ibm.com>]

On Mon, Nov 26, 2018 at 01:55:37PM +0000, Ran Rozenstein wrote:
> > 
> > Hearing no objections, here is the updated patch.
> > 
> > 								Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 970cab5d3d206029ed27274a98ea1c3d7e780e53
> > Author: Paul E. McKenney <paulmck@linux.ibm.com>
> > Date:   Mon Oct 29 07:36:50 2018 -0700
> > 
> >     rcu: Avoid signed integer overflow in rcu_preempt_deferred_qs()
> > 
> >     Subtracting INT_MIN can be interpreted as unconditional signed integer
> >     overflow, which according to the C standard is undefined behavior.
> >     Therefore, kernel build arguments notwithstanding, it would be good to
> >     future-proof the code.  This commit therefore substitutes INT_MAX for
> >     INT_MIN in order to avoid undefined behavior.
> > 
> >     While in the neighborhood, this commit also creates some meaningful
> > names
> >     for INT_MAX and friends in order to improve readability, as suggested
> >     by Joel Fernandes.
> > 
> >     Reported-by: Ran Rozenstein <ranro@mellanox.com>
> >     Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
> > 
> >     squash! rcu: Avoid signed integer overflow in rcu_preempt_deferred_qs()
> > 
> >     While in the neighborhood, use macros to give meaningful names.
> > 
> >     Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
> 
> Hi,
> 
> What is the acceptance status of this patch?

It is queued in -rcu.  If no problems arise beforehand, I intend to submit
it as part of a pull request into -tip, which (again if no problems arise)
be pulled into mainline during the next merge window.

Oddly enough, a couple of weeks ago the C++ Standards Committee voted
in a proposal for C++20 removing undefined behavior for signed integer
overflow.  This is C++ rather than C, and C must support additional
hardware that wouldn't much like forcing twos complement for signed
integer overflow.  But still...  ;-)

							Thanx, Paul