From: Kirill Tkhai <ktk...@parallels.com>
We may pick a task which is in context_switch() on other cpu at the moment.
Parallel using of a single stack by two processes is not a good idea.
Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
Cc: <sta...@vger.kernel.org>
---
kernel/sched/core.c | 11 +----------
kernel/sched/deadline.c | 7 ++++++-
kernel/sched/fair.c | 3 +++
kernel/sched/rt.c | 7 ++++++-
kernel/sched/sched.h | 16 ++++++++++++++++
5 files changed, 32 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 55d86e7..c8d754f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1699,16 +1699,7 @@ try_to_wake_up(struct task_struct *p, unsigned int
state, int wake_flags)
goto stat;
#ifdef CONFIG_SMP
- /*
- * If the owning (remote) cpu is still in the middle of schedule() with
- * this task as prev, wait until its done referencing the task.
- */
- while (p->on_cpu)
- cpu_relax();
- /*
- * Pairs with the smp_wmb() in finish_lock_switch().
- */
- smp_rmb();
+ cpu_relax__while_on_cpu(p);
p->sched_contributes_to_load = !!task_contributes_to_load(p);
p->state = TASK_WAKING;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index aaa5abb..ea0ba33 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1364,7 +1364,9 @@ static int push_dl_task(struct rq *rq)
next_task = task;
goto retry;
}
-
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ cpu_relax__while_on_cpu(next_task);
+#endif
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, later_rq->cpu);
activate_task(later_rq, next_task, 0);
@@ -1451,6 +1453,9 @@ static int pull_dl_task(struct rq *this_rq)
ret = 1;
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ cpu_relax__while_on_cpu(p);
+#endif
deactivate_task(src_rq, p, 0);
set_task_cpu(p, this_cpu);
activate_task(this_rq, p, 0);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fa13f94..0ec070e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5298,6 +5298,9 @@ int can_migrate_task(struct task_struct *p, struct lb_env
*env)
schedstat_inc(env->sd, lb_hot_gained[env->idle]);
schedstat_inc(p, se.statistics.nr_forced_migrations);
}
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ cpu_relax__while_on_cpu(p);
+#endif
return 1;
}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 2e6a774..de356b0 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1734,7 +1734,9 @@ static int push_rt_task(struct rq *rq)
next_task = task;
goto retry;
}
-
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ cpu_relax__while_on_cpu(next_task);
+#endif
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, lowest_rq->cpu);
activate_task(lowest_rq, next_task, 0);
@@ -1823,6 +1825,9 @@ static int pull_rt_task(struct rq *this_rq)
ret = 1;
+#ifdef __ARCH_WANT_UNLOCKED_CTXSW
+ cpu_relax__while_on_cpu(p);
+#endif
deactivate_task(src_rq, p, 0);
set_task_cpu(p, this_cpu);
activate_task(this_rq, p, 0);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index aa0f73b..e2ef9b7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1034,6 +1034,22 @@ static inline void finish_lock_switch(struct rq *rq,
struct task_struct *prev)
#endif /* __ARCH_WANT_UNLOCKED_CTXSW */
/*
+ * If the owning (remote) cpu is still in the middle of schedule() with
+ * this task as prev, wait until its done referencing the task.
+ */
+static inline void cpu_relax__while_on_cpu(struct task_struct *p)
+{
+#ifdef CONFIG_SMP
+ while (p->on_cpu)
+ cpu_relax();
+ /*
+ * Pairs with the smp_wmb() in finish_lock_switch().
+ */
+ smp_rmb();
+#endif
+}
+
+/*
* wake flags
*/
#define WF_SYNC 0x01 /* waker goes to sleep after
wakeup */
--
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