Preempt-RCU: Use softirq instead of tasklets for RCU
From: Dipankar Sarma <[email protected]>
This patch makes RCU use softirq instead of tasklets.
It also adds a memory barrier after raising the softirq
inorder to ensure that the cpu sees the most recently updated
value of rcu->cur while processing callbacks.
The discussion of the related theoretical race pointed out
by James Huang can be found here --> http://lkml.org/lkml/2007/11/20/603
Signed-off-by: Gautham R Shenoy <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Dipankar Sarma <[email protected]>
---
include/linux/interrupt.h | 1 +
kernel/rcupdate.c | 25 +++++++++++++++++--------
2 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 2306920..c3db4a0 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -256,6 +256,7 @@ enum
#ifdef CONFIG_HIGH_RES_TIMERS
HRTIMER_SOFTIRQ,
#endif
+ RCU_SOFTIRQ, /* Preferable RCU should always be the last softirq */
};
/* softirq mask and active fields moved to irq_cpustat_t in
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index a66d4d1..8658948 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -73,8 +73,6 @@ static struct rcu_ctrlblk rcu_bh_ctrlblk = {
DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
-/* Fake initialization required by compiler */
-static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
static int blimit = 10;
static int qhimark = 10000;
static int qlowmark = 100;
@@ -231,6 +229,18 @@ void rcu_barrier(void)
}
EXPORT_SYMBOL_GPL(rcu_barrier);
+/* Raises the softirq for processing rcu_callbacks. */
+static inline void raise_rcu_softirq(void)
+{
+ raise_softirq(RCU_SOFTIRQ);
+ /*
+ * The smp_mb() here is required to ensure that this cpu's
+ * __rcu_process_callbacks() reads the most recently updated
+ * value of rcu->cur.
+ */
+ smp_mb();
+}
+
/*
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
@@ -260,7 +270,7 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (!rdp->donelist)
rdp->donetail = &rdp->donelist;
else
- tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
+ raise_rcu_softirq();
}
/*
@@ -412,7 +422,6 @@ static void rcu_offline_cpu(int cpu)
&per_cpu(rcu_bh_data, cpu));
put_cpu_var(rcu_data);
put_cpu_var(rcu_bh_data);
- tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
}
#else
@@ -424,7 +433,7 @@ static void rcu_offline_cpu(int cpu)
#endif
/*
- * This does the RCU processing work from tasklet context.
+ * This does the RCU processing work from softirq context.
*/
static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
struct rcu_data *rdp)
@@ -469,7 +478,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
rcu_do_batch(rdp);
}
-static void rcu_process_callbacks(unsigned long unused)
+static void rcu_process_callbacks(struct softirq_action *unused)
{
__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
@@ -533,7 +542,7 @@ void rcu_check_callbacks(int cpu, int user)
rcu_bh_qsctr_inc(cpu);
} else if (!in_softirq())
rcu_bh_qsctr_inc(cpu);
- tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
+ raise_rcu_softirq();
}
static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
@@ -556,7 +565,7 @@ static void __devinit rcu_online_cpu(int cpu)
rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
- tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks, NULL);
}
static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
