linux-kernel - Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules

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Date:   Tue, 9 Apr 2019 14:04:11 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     paulmck <paulmck@...ux.ibm.com>
Cc:     "Joel Fernandes, Google" <joel@...lfernandes.org>,
        rcu <rcu@...r.kernel.org>,
        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>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        amd-gfx <amd-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules

----- On Apr 9, 2019, at 1:55 PM, paulmck paulmck@...ux.ibm.com wrote:
[...]
> The current state is not horrible, so my thought would be to give it
> some time to see if better thoughts arise.
> 
> Either way, cleanup_srcu_struct() keeps its current checks for callbacks
> still being in flight, which is why I believe that the current state is
> not horrible.  ;-)

In that case, I think the comment above cleanup_srcu_struct_quiesced() in
include/linux/srcu.h needs to be updated to cover situations where API
users statically define a SRCU domain in a module and intend to unload
that module.

Given that we end up doing the allocation/cleanup under the hood, the
API users don't interact with init_srcu_struct() nor cleanup_srcu_struct(),
so it's not obvious that this comment also applies to them.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com