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Message-ID: <20120706162708.GU2522@linux.vnet.ibm.com>
Date: Fri, 6 Jul 2012 09:27:09 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Alessio Igor Bogani <abogani@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Avi Kivity <avi@...hat.com>,
Chris Metcalf <cmetcalf@...era.com>,
Christoph Lameter <cl@...ux.com>,
Geoff Levand <geoff@...radead.org>,
Gilad Ben Yossef <gilad@...yossef.com>,
Hakan Akkan <hakanakkan@...il.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Josh Triplett <josh@...htriplett.org>,
Kevin Hilman <khilman@...com>,
Max Krasnyansky <maxk@...lcomm.com>,
Peter Zijlstra <peterz@...radead.org>,
Stephen Hemminger <shemminger@...tta.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/6] rcu: Allow rcu_user_enter()/exit() to nest
On Fri, Jul 06, 2012 at 02:00:14PM +0200, Frederic Weisbecker wrote:
> Allow calls to rcu_user_enter() even if we are already
> in userspace (as seen by RCU) and allow calls to rcu_user_exit()
> even if we are already in the kernel.
>
> This makes the APIs more flexible to be called from architectures.
> Exception entries for example won't need to know if they come from
> userspace before calling rcu_user_exit().
You lost me on this one. As long as the nesting level stays below
a few tens, rcu_user_enter() and rcu_user_exit() already can nest.
Or are you saying that you need to deal with duplicate rcu_user_enter()
calls that must be matched by a single rcu_user_exit() call?
Thanx, Paul
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Alessio Igor Bogani <abogani@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Avi Kivity <avi@...hat.com>
> Cc: Chris Metcalf <cmetcalf@...era.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Geoff Levand <geoff@...radead.org>
> Cc: Gilad Ben Yossef <gilad@...yossef.com>
> Cc: Hakan Akkan <hakanakkan@...il.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: Kevin Hilman <khilman@...com>
> Cc: Max Krasnyansky <maxk@...lcomm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephen Hemminger <shemminger@...tta.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
> kernel/rcutree.c | 38 ++++++++++++++++++++++++++++++--------
> 1 files changed, 30 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 64fc2cd..81a86ec 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -344,6 +344,10 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
> return 0;
> }
>
> +#ifdef CONFIG_RCU_USER_QS
> +static DEFINE_PER_CPU(bool, in_user);
> +#endif
> +
> /*
> * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
> *
> @@ -389,11 +393,9 @@ static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
> */
> static void rcu_eqs_enter(bool user)
> {
> - unsigned long flags;
> long long oldval;
> struct rcu_dynticks *rdtp;
>
> - local_irq_save(flags);
> rdtp = &__get_cpu_var(rcu_dynticks);
> oldval = rdtp->dynticks_nesting;
> WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
> @@ -402,7 +404,6 @@ static void rcu_eqs_enter(bool user)
> else
> rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
> rcu_eqs_enter_common(rdtp, oldval, user);
> - local_irq_restore(flags);
> }
>
> /**
> @@ -419,7 +420,11 @@ static void rcu_eqs_enter(bool user)
> */
> void rcu_idle_enter(void)
> {
> + unsigned long flags;
> +
> + local_irq_save(flags);
> rcu_eqs_enter(0);
> + local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_idle_enter);
>
> @@ -434,7 +439,16 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter);
> */
> void rcu_user_enter(void)
> {
> - rcu_eqs_enter(1);
> + unsigned long flags;
> +
> + WARN_ON_ONCE(!current->mm);
> +
> + local_irq_save(flags);
> + if (!this_cpu_read(in_user)) {
> + this_cpu_write(in_user, true);
> + rcu_eqs_enter(1);
> + }
> + local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_user_enter);
> #endif
> @@ -530,11 +544,9 @@ static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
> */
> static void rcu_eqs_exit(bool user)
> {
> - unsigned long flags;
> struct rcu_dynticks *rdtp;
> long long oldval;
>
> - local_irq_save(flags);
> rdtp = &__get_cpu_var(rcu_dynticks);
> oldval = rdtp->dynticks_nesting;
> WARN_ON_ONCE(oldval < 0);
> @@ -543,7 +555,6 @@ static void rcu_eqs_exit(bool user)
> else
> rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
> rcu_eqs_exit_common(rdtp, oldval, user);
> - local_irq_restore(flags);
> }
>
> /**
> @@ -559,7 +570,11 @@ static void rcu_eqs_exit(bool user)
> */
> void rcu_idle_exit(void)
> {
> + unsigned long flags;
> +
> + local_irq_save(flags);
> rcu_eqs_exit(0);
> + local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_idle_exit);
>
> @@ -572,7 +587,14 @@ EXPORT_SYMBOL_GPL(rcu_idle_exit);
> */
> void rcu_user_exit(void)
> {
> - rcu_eqs_exit(1);
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + if (this_cpu_read(in_user)) {
> + this_cpu_write(in_user, false);
> + rcu_eqs_exit(1);
> + }
> + local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_user_exit);
> #endif
> --
> 1.7.5.4
>
--
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