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

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Date:   Mon, 12 Nov 2018 09:07:50 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     paulmck <paulmck@...ux.ibm.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        dipankar <dipankar@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        fweisbec <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH tip/core/rcu 0/41] More RCU flavor consolidation cleanup
 for v4.21/v5.0

----- On Nov 11, 2018, at 2:41 PM, paulmck paulmck@...ux.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.
http://www.efficios.com