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Date: Wed, 24 Jan 2018 22:20:31 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: lianglihao@...wei.com
Cc: guohanjun@...wei.com, heng.z@...wei.com, hb.chen@...wei.com,
lihao.liang@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 07/16] prcu: Implement call_prcu() API
On Tue, Jan 23, 2018 at 03:59:32PM +0800, lianglihao@...wei.com wrote:
> From: Lihao Liang <lianglihao@...wei.com>
>
> This is PRCU's counterpart of RCU's call_rcu() API.
>
> Reviewed-by: Heng Zhang <heng.z@...wei.com>
> Signed-off-by: Lihao Liang <lianglihao@...wei.com>
> ---
> include/linux/prcu.h | 25 ++++++++++++++++++++
> init/main.c | 2 ++
> kernel/rcu/prcu.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++---
> 3 files changed, 91 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/prcu.h b/include/linux/prcu.h
> index 653b4633..e5e09c9b 100644
> --- a/include/linux/prcu.h
> +++ b/include/linux/prcu.h
> @@ -2,15 +2,36 @@
> #define __LINUX_PRCU_H
>
> #include <linux/atomic.h>
> +#include <linux/types.h>
> #include <linux/mutex.h>
> #include <linux/wait.h>
>
> #define CONFIG_PRCU
>
> +struct prcu_version_head {
> + unsigned long long version;
> + struct prcu_version_head *next;
> +};
> +
> +/* Simple unsegmented callback list for PRCU. */
> +struct prcu_cblist {
> + struct rcu_head *head;
> + struct rcu_head **tail;
> + struct prcu_version_head *version_head;
> + struct prcu_version_head **version_tail;
> + long len;
> +};
> +
> +#define PRCU_CBLIST_INITIALIZER(n) { \
> + .head = NULL, .tail = &n.head, \
> + .version_head = NULL, .version_tail = &n.version_head, \
> +}
> +
> struct prcu_local_struct {
> unsigned int locked;
> unsigned int online;
> unsigned long long version;
> + struct prcu_cblist cblist;
> };
>
> struct prcu_struct {
> @@ -24,6 +45,8 @@ struct prcu_struct {
> void prcu_read_lock(void);
> void prcu_read_unlock(void);
> void synchronize_prcu(void);
> +void call_prcu(struct rcu_head *head, rcu_callback_t func);
> +void prcu_init(void);
> void prcu_note_context_switch(void);
>
> #else /* #ifdef CONFIG_PRCU */
> @@ -31,6 +54,8 @@ void prcu_note_context_switch(void);
> #define prcu_read_lock() do {} while (0)
> #define prcu_read_unlock() do {} while (0)
> #define synchronize_prcu() do {} while (0)
> +#define call_prcu() do {} while (0)
> +#define prcu_init() do {} while (0)
> #define prcu_note_context_switch() do {} while (0)
>
> #endif /* #ifdef CONFIG_PRCU */
> diff --git a/init/main.c b/init/main.c
> index f8665104..4925964e 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -38,6 +38,7 @@
> #include <linux/smp.h>
> #include <linux/profile.h>
> #include <linux/rcupdate.h>
> +#include <linux/prcu.h>
> #include <linux/moduleparam.h>
> #include <linux/kallsyms.h>
> #include <linux/writeback.h>
> @@ -574,6 +575,7 @@ asmlinkage __visible void __init start_kernel(void)
> workqueue_init_early();
>
> rcu_init();
> + prcu_init();
>
> /* Trace events are available after this */
> trace_init();
> diff --git a/kernel/rcu/prcu.c b/kernel/rcu/prcu.c
> index a00b9420..f198285c 100644
> --- a/kernel/rcu/prcu.c
> +++ b/kernel/rcu/prcu.c
> @@ -1,11 +1,12 @@
> #include <linux/smp.h>
> -#include <linux/prcu.h>
> #include <linux/percpu.h>
> -#include <linux/compiler.h>
> +#include <linux/prcu.h>
> #include <linux/sched.h>
> -
> +#include <linux/slab.h>
> #include <asm/barrier.h>
>
> +#include "rcu.h"
> +
> DEFINE_PER_CPU_SHARED_ALIGNED(struct prcu_local_struct, prcu_local);
>
> struct prcu_struct global_prcu = {
> @@ -16,6 +17,16 @@ struct prcu_struct global_prcu = {
> };
> struct prcu_struct *prcu = &global_prcu;
>
> +/* Initialize simple callback list. */
> +static void prcu_cblist_init(struct prcu_cblist *rclp)
> +{
> + rclp->head = NULL;
> + rclp->tail = &rclp->head;
> + rclp->version_head = NULL;
> + rclp->version_tail = &rclp->version_head;
> + rclp->len = 0;
> +}
> +
> static inline void prcu_report(struct prcu_local_struct *local)
> {
> unsigned long long global_version;
> @@ -123,3 +134,53 @@ void prcu_note_context_switch(void)
> prcu_report(local);
> put_cpu_ptr(&prcu_local);
> }
> +
> +void call_prcu(struct rcu_head *head, rcu_callback_t func)
> +{
> + unsigned long flags;
> + struct prcu_local_struct *local;
> + struct prcu_cblist *rclp;
> + struct prcu_version_head *vhp;
> +
> + debug_rcu_head_queue(head);
> +
> + /* Use GFP_ATOMIC with IRQs disabled */
> + vhp = kmalloc(sizeof(struct prcu_version_head), GFP_ATOMIC);
> + if (!vhp)
> + return;
Silently failing to post the callback can cause system hangs. I suggest
finding some way to avoid allocating on the call_prcu() code path.
Thanx, Paul
> +
> + head->func = func;
> + head->next = NULL;
> + vhp->next = NULL;
> +
> + local_irq_save(flags);
> + local = this_cpu_ptr(&prcu_local);
> + vhp->version = local->version;
> + rclp = &local->cblist;
> + rclp->len++;
> + *rclp->tail = head;
> + rclp->tail = &head->next;
> + *rclp->version_tail = vhp;
> + rclp->version_tail = &vhp->next;
> + local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL(call_prcu);
> +
> +void prcu_init_local_struct(int cpu)
> +{
> + struct prcu_local_struct *local;
> +
> + local = per_cpu_ptr(&prcu_local, cpu);
> + local->locked = 0;
> + local->online = 0;
> + local->version = 0;
> + prcu_cblist_init(&local->cblist);
> +}
> +
> +void __init prcu_init(void)
> +{
> + int cpu;
> +
> + for_each_possible_cpu(cpu)
> + prcu_init_local_struct(cpu);
> +}
> --
> 2.14.1.729.g59c0ea183
>
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