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Subject[PATCH 1/1] sched: make finish_task_switch() return struct rq *
Both callers of finish_task_switch() need to recalculate this_rq()
and pass it as an argument, plus __schedule() does this again after
context_switch().

It would be simpler to call this_rq() once in finish_task_switch()
and return the this rq to the callers.

Note: probably "int cpu" in __schedule() should die; it is not used
and both rcu_note_context_switch() and wq_worker_sleeping() do not
really need this argument.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/sched/core.c | 37 +++++++++++++++----------------------
1 files changed, 15 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cfe9905..3bfbd3d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2200,10 +2200,16 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev,
* so, we finish that here outside of the runqueue lock. (Doing it
* with the lock held can cause deadlocks; see schedule() for
* details.)
+ *
+ * The context switch have flipped the stack from under us and restored the
+ * local variables which were saved when this task called schedule() in the
+ * past. prev == current is still correct but we need to recalculate this_rq
+ * because prev may have moved to another CPU.
*/
-static void finish_task_switch(struct rq *rq, struct task_struct *prev)
+static struct rq *finish_task_switch(struct task_struct *prev)
__releases(rq->lock)
{
+ struct rq *rq = this_rq();
struct mm_struct *mm = rq->prev_mm;
long prev_state;

@@ -2243,6 +2249,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
}

tick_nohz_task_switch(current);
+ return rq;
}

#ifdef CONFIG_SMP
@@ -2281,8 +2288,7 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)

/* finish_task_switch() drops rq->lock and enables preemtion */
preempt_disable();
- rq = this_rq();
- finish_task_switch(rq, prev);
+ rq = finish_task_switch(prev);
post_schedule(rq);
preempt_enable();

@@ -2291,10 +2297,9 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
}

/*
- * context_switch - switch to the new MM and the new
- * thread's register state.
+ * context_switch - switch to the new MM and the new thread's register state.
*/
-static inline void
+static inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
struct task_struct *next)
{
@@ -2335,14 +2340,9 @@ context_switch(struct rq *rq, struct task_struct *prev,
context_tracking_task_switch(prev, next);
/* Here we just switch the register state and the stack. */
switch_to(prev, next, prev);
-
barrier();
- /*
- * this_rq must be evaluated again because prev may have moved
- * CPUs since it called schedule(), thus the 'rq' on its stack
- * frame will be invalid.
- */
- finish_task_switch(this_rq(), prev);
+
+ return finish_task_switch(prev);
}

/*
@@ -2802,15 +2802,8 @@ need_resched:
rq->curr = next;
++*switch_count;

- context_switch(rq, prev, next); /* unlocks the rq */
- /*
- * The context switch have flipped the stack from under us
- * and restored the local variables which were saved when
- * this task called schedule() in the past. prev == current
- * is still correct, but it can be moved to another cpu/rq.
- */
- cpu = smp_processor_id();
- rq = cpu_rq(cpu);
+ rq = context_switch(rq, prev, next); /* unlocks the rq */
+ cpu = rq->cpu;
} else
raw_spin_unlock_irq(&rq->lock);

--
1.5.5.1



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