Re: [PATCH] Add list_for_each_rcu to features-removal list

From: Paul E. McKenney
Date: Sat Feb 16 2008 - 11:20:20 EST


On Sat, Feb 16, 2008 at 10:47:23AM +0200, Adrian Bunk wrote:
> On Mon, Jan 28, 2008 at 04:25:00AM -0800, Paul E. McKenney wrote:
> > Hello!
> >
> > The list_for_each_entry_rcu() primitive should be used instead of
> > list_for_each_rcu(), as the former is easier to use and provides
> > better type safety. This patch therefore adds list_for_each_rcu()
> > to the Documentation/feature-removal-schedule.txt file (for mid-2008)
> > and marks its comment header deprecated.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > ---
> >
> > Documentation/feature-removal-schedule.txt | 10 ++++++++++
> > include/linux/list.h | 5 ++++-
> > 2 files changed, 14 insertions(+), 1 deletion(-)
> >
> > diff -urpNa -X dontdiff linux-2.6.24/Documentation/feature-removal-schedule.txt linux-2.6.24-dep-lfeRCU/Documentation/feature-removal-schedule.txt
> > --- linux-2.6.24/Documentation/feature-removal-schedule.txt 2008-01-24 14:58:37.000000000 -0800
> > +++ linux-2.6.24-dep-lfeRCU/Documentation/feature-removal-schedule.txt 2008-01-28 04:00:49.000000000 -0800
> > @@ -333,3 +333,13 @@ Why: This driver has been marked obsolet
> > Who: Stephen Hemminger <shemminger@xxxxxxxxxxxxxxxxxxxx>
> >
> > ---------------------------
> > +
> > +What: list_for_each_rcu() primitive
> > +When: July 2008
> > +Files: include/linux/list.h
> > +Why: The list_for_each_entry_rcu() primitive should be used instead,
> > + as it is less error-prone and provides better type safety.
> > +Who: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> >...
>
> Declaring something as deprecated doesn't automatically convert the
> in-kernel users.

Understood.

> And once there are no in-kernel users left you can kill it immediately.

Hmmm... What is the purpose of Documentation/feature-removal-schedule.txt
in that case?

> The only working way for getting rid of list_for_each_rcu() is:
> - send patches for all in-kernel usages to the maintainers of the code
> in question now

That has happened at least once.

> - once all of these patches have entered Linus' tree (which might not
> be before the 2.6.26 merge window) you can remove list_for_each_rcu()

So your approach would be to mark the macro obsolete to prevent additional
uses in the meantime?

Thanx, Paul
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