Commit-ID: 19dd1591fc379f1d89f39cd99cbbe97433baa3c3
Gitweb: http://git.kernel.org/tip/19dd1591fc379f1d89f39cd99cbbe97433baa3c3
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
AuthorDate: Mon, 4 Jun 2012 16:42:35 -0700
Committer: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CommitDate: Wed, 26 Sep 2012 15:44:01 +0200
rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIs
In some cases, it is necessary to enter or exit userspace-RCU-idle mode
from an interrupt handler, for example, if some other CPU sends this
CPU a resched IPI. In this case, the current CPU would enter the IPI
handler in userspace-RCU-idle mode, but would need to exit the IPI handler
after having exited that mode.
To allow this to work, this commit adds two new APIs to TREE_RCU:
- rcu_user_enter_after_irq(). This must be called from an interrupt between
rcu_irq_enter() and rcu_irq_exit(). After the irq calls rcu_irq_exit(),
the irq handler will return into an RCU extended quiescent state.
In theory, this interrupt is never a nested interrupt, but in practice
it might interrupt softirq, which looks to RCU like a nested interrupt.
- rcu_user_exit_after_irq(). This must be called from a non-nesting
interrupt, interrupting an RCU extended quiescent state, also
between rcu_irq_enter() and rcu_irq_exit(). After the irq calls
rcu_irq_exit(), the irq handler will return in an RCU non-quiescent
state.
[ Combined with "Allow calls to rcu_exit_user_irq from nesting irqs." ]
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
---
include/linux/rcupdate.h | 2 ++
kernel/rcutree.c | 43 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+), 0 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d8b20bf..f818dd1 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -193,6 +193,8 @@ extern void rcu_irq_enter(void);
extern void rcu_irq_exit(void);
extern void rcu_user_enter(void);
extern void rcu_user_exit(void);
+extern void rcu_user_enter_after_irq(void);
+extern void rcu_user_exit_after_irq(void);
extern void exit_rcu(void);
/**
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index af0dc34..4138f59 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -426,6 +426,27 @@ void rcu_user_enter(void)
/**
+ * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
+ * after the current irq returns.
+ *
+ * This is similar to rcu_user_enter() but in the context of a non-nesting
+ * irq. After this call, RCU enters into idle mode when the interrupt
+ * returns.
+ */
+void rcu_user_enter_after_irq(void)
+{
+ unsigned long flags;
+ struct rcu_dynticks *rdtp;
+
+ local_irq_save(flags);
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ /* Ensure this irq is interrupting a non-idle RCU state. */
+ WARN_ON_ONCE(!(rdtp->dynticks_nesting & DYNTICK_TASK_MASK));
+ rdtp->dynticks_nesting = 1;
+ local_irq_restore(flags);
+}
+
+/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
*
* Exit from an interrupt handler, which might possibly result in entering
@@ -550,6 +571,28 @@ void rcu_user_exit(void)
}
/**
+ * rcu_user_exit_after_irq - inform RCU that we won't resume to userspace
+ * idle mode after the current non-nesting irq returns.
+ *
+ * This is similar to rcu_user_exit() but in the context of an irq.
+ * This is called when the irq has interrupted a userspace RCU idle mode
+ * context. When the current non-nesting interrupt returns after this call,
+ * the CPU won't restore the RCU idle mode.
+ */
+void rcu_user_exit_after_irq(void)
+{
+ unsigned long flags;
+ struct rcu_dynticks *rdtp;
+
+ local_irq_save(flags);
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ /* Ensure we are interrupting an RCU idle mode. */
+ WARN_ON_ONCE(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK);
+ rdtp->dynticks_nesting += DYNTICK_TASK_EXIT_IDLE;
+ local_irq_restore(flags);
+}
+
+/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
*
* Enter an interrupt handler, which might possibly result in exiting
--
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