Re: [PATCH 00/13] Rename k[v]free_rcu() single argument to k[v]free_rcu_mightsleep()

[Paul E. McKenney]

On Thu, Feb 23, 2023 at 12:36:57PM -0700, Jens Axboe wrote:
> On 2/23/23 11:31 AM, Paul E. McKenney wrote:
> > On Thu, Feb 23, 2023 at 07:57:13AM -0700, Jens Axboe wrote:
> >> On 2/1/23 8:08 AM, Uladzislau Rezki (Sony) wrote:
> >>> This small series is based on Paul's "dev" branch. Head is 6002817348a1c610dc1b1c01ff81654cdec12be4
> >>> it renames a single argument of k[v]free_rcu() to its new k[v]free_rcu_mightsleep() name.
> >>>
> >>> 1.
> >>> The problem is that, recently we have run into a precedent when
> >>> a user intended to give a second argument to kfree_rcu() API but
> >>> forgot to do it in a code so a call became as a single argument
> >>> of kfree_rcu() API.
> >>>
> >>> 2.
> >>> Such mistyping can lead to hidden bags where sleeping is forbidden.
> >>>
> >>> 3.
> >>> _mightsleep() prefix gives much more information for which contexts
> >>> it can be used for.
> >>
> >> This patchset seems weird to me. We have a LOT of calls that might
> >> sleep, yet we don't suffix them all with _mightsleep(). Why is this
> >> any different? Why isn't this just a might_sleep() call in the
> >> actual helper, which will suffice for checkers and catch it at
> >> runtime as well.
> > 
> > Fair enough, and the situation that this patchset is addressing is also a
> > bit unusual.  This change was requested by Eric Dumazet due to a situation
> > where someone forgot the optional second argument to kfree_rcu().  Now,
> > you are right that this would be caught if invoked from a non-sleepable
> > context, but there are also cases where sleeping is legal, but where the
> > occasional wait for an RCU grace period would be a problem.  The checkers
> > cannot easily catch this sort of thing, and hence the change in name.
> > 
> > Hey, the combined one/two-argument form seemed like a good idea at
> > the time!  ;-)
> 
> Hah, not sure what you were smoking back then!

If I remember, would you like me to send you some?  ;-)

							Thanx, Paul