Re: [PATCH tip/core/rcu 0/41] More RCU flavor consolidation cleanup for v4.21/v5.0

Mathieu Desnoyers
2018-11-12T14:07:54Z

----- On Nov 11, 2018, at 2:41 PM, paulmck paulmck@linux.ibm.com wrote:

> Hello!
>
> This series does additional cleanup for the RCU flavor consolidation,
> focusing primarily on uses of old API members, for example, so that
> call_rcu_bh() becomes call_rcu(). There are also a few straggling
> internal-to-RCU cleanups.
>
> 1. Remove unused rcu_state externs, courtesy of Joel Fernandes.
>
> 2. Fix rcu_{node,data} comments about gp_seq_needed, courtesy of
> Joel Fernandes.
>
> 3. Eliminate synchronize_rcu_mult() and its sole caller.
>
> 4. Consolidate the RCU update functions invoked by sync.c.
>
> 5-41. Replace old flavorful RCU API calls with the corresponding
> vanilla calls.

Hi Paul,

Just a heads up: we might want to spell out warnings in very big letters
for anyone trying to backport code using RCU from post-4.21 kernels
back to older kernels. I fear that newer code will build just fine
on older kernels, but will spectacularly fail in hard-to-debug ways at
runtime.

Renaming synchronize_rcu() and call_rcu() to something that did not
exist in prior kernels would prevent that. It may not be as pretty
though.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.