From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
rcu@vger.kernel.org, linux-kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
dipankar <dipankar@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
rostedt <rostedt@goodmis.org>,
David Howells <dhowells@redhat.com>,
Eric Dumazet <edumazet@google.com>, fweisbec <fweisbec@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
linux-nvdimm@lists.01.org, dri-devel@lists.freedesktop.org,
amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules
Date: Wed, 3 Apr 2019 06:19:18 -0700 [thread overview]
Message-ID: <20190403131918.GD4102@linux.ibm.com> (raw)
In-Reply-To: <20190402184054.GA18150@google.com>
On Tue, Apr 02, 2019 at 02:40:54PM -0400, Joel Fernandes wrote:
> On Tue, Apr 02, 2019 at 08:23:34AM -0700, Paul E. McKenney wrote:
> > On Tue, Apr 02, 2019 at 11:14:40AM -0400, Mathieu Desnoyers wrote:
> > > ----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck@linux.ibm.com wrote:
> > >
> > > > Hello!
> > > >
> > > > This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU()
> > > > by loadable modules. The reason for this prohibition is the fact
> > > > that using these two macros within modules requires that the size of
> > > > the reserved region be increased, which is not something we want to
> > > > be doing all that often. Instead, loadable modules should define an
> > > > srcu_struct and invoke init_srcu_struct() from their module_init function
> > > > and cleanup_srcu_struct() from their module_exit function. Note that
> > > > modules using call_srcu() will also need to invoke srcu_barrier() from
> > > > their module_exit function.
> > >
> > > This arbitrary API limitation seems weird.
> > >
> > > Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU
> > > while implementing them with dynamic allocation under the hood ?
> >
> > Although call_srcu() already has initialization hooks, some would
> > also be required in srcu_read_lock(), and I am concerned about adding
> > memory allocation at that point, especially given the possibility
> > of memory-allocation failure. And the possibility that the first
> > srcu_read_lock() happens in an interrupt handler or similar.
> >
> > Or am I missing a trick here?
>
> Hi Paul,
>
> Which 'reserved region' are you referring to? Isn't this region also
> used for non-module cases in which case the same problem applies to
> non-modules?
The percpu/module reservation discussed in this thread:
https://lore.kernel.org/lkml/c72402f2-967e-cd56-99d8-9139c9e7f267@google.com/T/#mbcacf60ddc0b3fd6e831a3ea71efc90da359a3bf
For non-modules, global per-CPU variables are statically allocated.
For modules, they must be dynamically allocated at modprobe time, and
their size is set by PERCPU_MODULE_RESERVE.
Thanx, Paul
prev parent reply other threads:[~2019-04-03 13:19 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-02 14:28 [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Paul E. McKenney
2019-04-02 14:29 ` [PATCH RFC tip/core/rcu 1/4] dax/super: Dynamically allocate dax_srcu Paul E. McKenney
2019-04-03 18:31 ` Dan Williams
2019-04-04 21:04 ` Paul E. McKenney
2019-04-02 14:29 ` [PATCH RFC tip/core/rcu 2/4] drivers/gpu/drm: Dynamically allocate drm_unplug_srcu Paul E. McKenney
2019-04-02 16:14 ` Daniel Vetter
2019-04-02 14:29 ` [PATCH RFC tip/core/rcu 3/4] drivers/gpu/drm/amd: Dynamically allocate kfd_processes_srcu Paul E. McKenney
2019-04-02 17:40 ` Kuehling, Felix
2019-04-04 21:16 ` Paul E. McKenney
2019-04-02 14:29 ` [PATCH RFC tip/core/rcu 4/4] rcu: Forbid DEFINE{,_STATIC}_SRCU() from modules Paul E. McKenney
2019-04-02 15:14 ` [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules Mathieu Desnoyers
2019-04-02 15:23 ` Paul E. McKenney
2019-04-02 15:34 ` Mathieu Desnoyers
2019-04-03 13:32 ` Paul E. McKenney
2019-04-03 14:27 ` Mathieu Desnoyers
2019-04-03 16:20 ` Paul E. McKenney
2019-04-03 19:30 ` Joel Fernandes
2019-04-05 23:28 ` Paul E. McKenney
2019-04-06 13:33 ` Joel Fernandes
2019-04-07 13:48 ` Paul E. McKenney
2019-04-06 23:06 ` Joel Fernandes
2019-04-07 13:39 ` Paul E. McKenney
2019-04-07 13:59 ` Paul E. McKenney
2019-04-07 15:46 ` Joel Fernandes
2019-04-07 17:05 ` Paul E. McKenney
2019-04-08 0:36 ` Joel Fernandes
2019-04-08 2:28 ` Paul E. McKenney
2019-04-07 19:26 ` Mathieu Desnoyers
2019-04-07 19:32 ` Joel Fernandes
2019-04-07 20:41 ` Mathieu Desnoyers
2019-04-07 21:07 ` Joel Fernandes
2019-04-08 2:27 ` Paul E. McKenney
2019-04-08 13:05 ` Mathieu Desnoyers
2019-04-08 14:22 ` Paul E. McKenney
2019-04-08 14:49 ` Mathieu Desnoyers
2019-04-08 15:46 ` Paul E. McKenney
2019-04-08 17:24 ` Mathieu Desnoyers
2019-04-09 15:40 ` Joel Fernandes
2019-04-09 15:56 ` Mathieu Desnoyers
2019-04-09 16:18 ` Joel Fernandes
2019-04-09 16:40 ` Paul E. McKenney
2019-04-09 16:45 ` Mathieu Desnoyers
2019-04-09 17:55 ` Paul E. McKenney
2019-04-09 18:04 ` Mathieu Desnoyers
2019-04-09 19:14 ` Paul E. McKenney
2019-04-02 18:40 ` Joel Fernandes
2019-04-03 13:19 ` Paul E. McKenney [this message]
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