From 154abafc68bfb7c2ef2ad5308a3b2de8968c3f61 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 14 Sep 2019 07:34:30 -0500 Subject: tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code Remove work arounds that were written before there was a grace period after tasks left the runqueue in finish_task_switch(). In particular now that there tasks exiting the runqueue exprience a RCU grace period none of the work performed by task_rcu_dereference() excpet the rcu_dereference() is necessary so replace task_rcu_dereference() with rcu_dereference(). Remove the code in rcuwait_wait_event() that checks to ensure the current task has not exited. It is no longer necessary as it is guaranteed that any running task will experience a RCU grace period after it leaves the run queueue. Remove the comment in rcuwait_wake_up() as it is no longer relevant. Ref: 8f95c90ceb54 ("sched/wait, RCU: Introduce rcuwait machinery") Ref: 150593bf8693 ("sched/api: Introduce task_rcu_dereference() and try_get_task_struct()") Signed-off-by: Eric W. Biederman Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Metcalf Cc: Christoph Lameter Cc: Davidlohr Bueso Cc: Kirill Tkhai Cc: Linus Torvalds Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Russell King - ARM Linux admin Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/87lfurdpk9.fsf_-_@x220.int.ebiederm.org Signed-off-by: Ingo Molnar --- include/linux/rcuwait.h | 20 ++++---------------- include/linux/sched/task.h | 1 - 2 files changed, 4 insertions(+), 17 deletions(-) (limited to 'include') diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h index 563290fc194f..75c97e4bbc57 100644 --- a/include/linux/rcuwait.h +++ b/include/linux/rcuwait.h @@ -6,16 +6,11 @@ /* * rcuwait provides a way of blocking and waking up a single - * task in an rcu-safe manner; where it is forbidden to use - * after exit_notify(). task_struct is not properly rcu protected, - * unless dealing with rcu-aware lists, ie: find_task_by_*(). + * task in an rcu-safe manner. * - * Alternatively we have task_rcu_dereference(), but the return - * semantics have different implications which would break the - * wakeup side. The only time @task is non-nil is when a user is - * blocked (or checking if it needs to) on a condition, and reset - * as soon as we know that the condition has succeeded and are - * awoken. + * The only time @task is non-nil is when a user is blocked (or + * checking if it needs to) on a condition, and reset as soon as we + * know that the condition has succeeded and are awoken. */ struct rcuwait { struct task_struct __rcu *task; @@ -37,13 +32,6 @@ extern void rcuwait_wake_up(struct rcuwait *w); */ #define rcuwait_wait_event(w, condition) \ ({ \ - /* \ - * Complain if we are called after do_exit()/exit_notify(), \ - * as we cannot rely on the rcu critical region for the \ - * wakeup side. \ - */ \ - WARN_ON(current->exit_state); \ - \ rcu_assign_pointer((w)->task, current); \ for (;;) { \ /* \ diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index 153a683646ac..4b1c3b664f51 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -119,7 +119,6 @@ static inline void put_task_struct(struct task_struct *t) __put_task_struct(t); } -struct task_struct *task_rcu_dereference(struct task_struct **ptask); void put_task_struct_rcu_user(struct task_struct *task); #ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT -- cgit v1.2.3