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-rw-r--r--kernel/exit.c67
-rw-r--r--kernel/sched/fair.c2
-rw-r--r--kernel/sched/membarrier.c4
3 files changed, 3 insertions, 70 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 3bcaec2ea3ba..a46a50d67002 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -234,69 +234,6 @@ repeat:
goto repeat;
}
-/*
- * Note that if this function returns a valid task_struct pointer (!NULL)
- * task->usage must remain >0 for the duration of the RCU critical section.
- */
-struct task_struct *task_rcu_dereference(struct task_struct **ptask)
-{
- struct sighand_struct *sighand;
- struct task_struct *task;
-
- /*
- * We need to verify that release_task() was not called and thus
- * delayed_put_task_struct() can't run and drop the last reference
- * before rcu_read_unlock(). We check task->sighand != NULL,
- * but we can read the already freed and reused memory.
- */
-retry:
- task = rcu_dereference(*ptask);
- if (!task)
- return NULL;
-
- probe_kernel_address(&task->sighand, sighand);
-
- /*
- * Pairs with atomic_dec_and_test() in put_task_struct(). If this task
- * was already freed we can not miss the preceding update of this
- * pointer.
- */
- smp_rmb();
- if (unlikely(task != READ_ONCE(*ptask)))
- goto retry;
-
- /*
- * We've re-checked that "task == *ptask", now we have two different
- * cases:
- *
- * 1. This is actually the same task/task_struct. In this case
- * sighand != NULL tells us it is still alive.
- *
- * 2. This is another task which got the same memory for task_struct.
- * We can't know this of course, and we can not trust
- * sighand != NULL.
- *
- * In this case we actually return a random value, but this is
- * correct.
- *
- * If we return NULL - we can pretend that we actually noticed that
- * *ptask was updated when the previous task has exited. Or pretend
- * that probe_slab_address(&sighand) reads NULL.
- *
- * If we return the new task (because sighand is not NULL for any
- * reason) - this is fine too. This (new) task can't go away before
- * another gp pass.
- *
- * And note: We could even eliminate the false positive if re-read
- * task->sighand once again to avoid the falsely NULL. But this case
- * is very unlikely so we don't care.
- */
- if (!sighand)
- return NULL;
-
- return task;
-}
-
void rcuwait_wake_up(struct rcuwait *w)
{
struct task_struct *task;
@@ -316,10 +253,6 @@ void rcuwait_wake_up(struct rcuwait *w)
*/
smp_mb(); /* (B) */
- /*
- * Avoid using task_rcu_dereference() magic as long as we are careful,
- * see comment in rcuwait_wait_event() regarding ->exit_state.
- */
task = rcu_dereference(w->task);
if (task)
wake_up_process(task);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3101c662426d..5bc23996ffae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1602,7 +1602,7 @@ static void task_numa_compare(struct task_numa_env *env,
return;
rcu_read_lock();
- cur = task_rcu_dereference(&dst_rq->curr);
+ cur = rcu_dereference(dst_rq->curr);
if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
cur = NULL;
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index aa8d75804108..b14250a11608 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -71,7 +71,7 @@ static int membarrier_global_expedited(void)
continue;
rcu_read_lock();
- p = task_rcu_dereference(&cpu_rq(cpu)->curr);
+ p = rcu_dereference(cpu_rq(cpu)->curr);
if (p && p->mm && (atomic_read(&p->mm->membarrier_state) &
MEMBARRIER_STATE_GLOBAL_EXPEDITED)) {
if (!fallback)
@@ -150,7 +150,7 @@ static int membarrier_private_expedited(int flags)
if (cpu == raw_smp_processor_id())
continue;
rcu_read_lock();
- p = task_rcu_dereference(&cpu_rq(cpu)->curr);
+ p = rcu_dereference(cpu_rq(cpu)->curr);
if (p && p->mm == current->mm) {
if (!fallback)
__cpumask_set_cpu(cpu, tmpmask);