On Wed, Nov 11, 2015 at 01:23:10PM +0100, Peter Zijlstra wrote:
> Hi
>
> I recently ran into TASKS_RCU() and wondered why we can't use normal
> coding patterns to do the same.
>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Well, I cannot get too excited either way, but the diffstat for this
change is not particularly favorable.
Thanx, Paul
> ---
> include/linux/rcupdate.h | 33 +++++++++++++++++++++++++++++++--
> kernel/exit.c | 9 +++------
> 2 files changed, 34 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index a0189ba67fde..15a82372b372 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -389,7 +389,7 @@ static inline void rcu_init_nohz(void)
> * macro rather than an inline function to avoid #include hell.
> */
> #ifdef CONFIG_TASKS_RCU
> -#define TASKS_RCU(x) x
> +
> extern struct srcu_struct tasks_rcu_exit_srcu;
> #define rcu_note_voluntary_context_switch(t) \
> do { \
> @@ -397,9 +397,38 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
> if (READ_ONCE((t)->rcu_tasks_holdout)) \
> WRITE_ONCE((t)->rcu_tasks_holdout, false); \
> } while (0)
> +
> +static inline int tasks_rcu_read_lock(void)
> +{
> + int idx;
> +
> + preempt_disable();
> + idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
> + preempt_enable();
> +
> + return idx;
> +}
> +
> +static inline void tasks_rcu_read_unlock(int idx)
> +{
> + preempt_disable();
> + __srcu_read_unlock(&tasks_rcu_exit_srcu, idx);
> + preempt_enable();
> +}
> +
> #else /* #ifdef CONFIG_TASKS_RCU */
> -#define TASKS_RCU(x) do { } while (0)
> +
> #define rcu_note_voluntary_context_switch(t) rcu_all_qs()
> +
> +static inline int tasks_rcu_read_lock(void)
> +{
> + return 0;
> +}
> +
> +static inline void tasks_rcu_read_unlock(int idx)
> +{
> +}
> +
> #endif /* #else #ifdef CONFIG_TASKS_RCU */
>
> /**
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 07110c6020a0..cd5644baeb22 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -653,8 +653,7 @@ static inline void check_stack_usage(void) {}
> void do_exit(long code)
> {
> struct task_struct *tsk = current;
> - int group_dead;
> - TASKS_RCU(int tasks_rcu_i);
> + int group_dead, tasks_rcu_i;
>
> profile_task_exit(tsk);
>
> @@ -763,9 +762,7 @@ void do_exit(long code)
> */
> flush_ptrace_hw_breakpoint(tsk);
>
> - TASKS_RCU(preempt_disable());
> - TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
> - TASKS_RCU(preempt_enable());
> + tasks_rcu_i = tasks_rcu_read_lock();
> exit_notify(tsk, group_dead);
> proc_exit_connector(tsk);
> #ifdef CONFIG_NUMA
> @@ -805,7 +802,7 @@ void do_exit(long code)
> if (tsk->nr_dirtied)
> __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
> exit_rcu();
> - TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
> + tasks_rcu_read_unlock(tasks_rcu_i);
>
> /*
> * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
>
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