From 456b1de166e9e555a1a1a0f99ed98d3c73b3de7e Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Wed, 28 Jul 2021 12:28:27 -0700
Subject: [PATCH] rcu-tasks: Remove second argument of
rcu_read_unlock_trace_special()
References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.16-rc1
Git-commit: a5c071ccfa1728508f31e61213ee795e4529d0d4
The second argument of rcu_read_unlock_trace_special() is always zero.
When called from exit_tasks_rcu_finish_trace(), it is the constant
zero, and rcu_read_unlock_trace_special() doesn't get called from
rcu_read_unlock_trace() unless the value of local variable "nesting"
is zero because in that case the early return is taken instead.
This commit therefore removes the "nesting" argument from the
rcu_read_unlock_trace_special() function, substituting the constant
zero within that function. This commit also adds a WARN_ON_ONCE()
to rcu_read_lock_trace_held() in case non-zeroness some day appears.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/linux/rcupdate_trace.h | 5 +++--
kernel/rcu/tasks.h | 6 +++---
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index 86c8f6c98412..6f9c35817398 100644
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -31,7 +31,7 @@ static inline int rcu_read_lock_trace_held(void)
#ifdef CONFIG_TASKS_TRACE_RCU
-void rcu_read_unlock_trace_special(struct task_struct *t, int nesting);
+void rcu_read_unlock_trace_special(struct task_struct *t);
/**
* rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section
@@ -80,7 +80,8 @@ static inline void rcu_read_unlock_trace(void)
WRITE_ONCE(t->trc_reader_nesting, nesting);
return; // We assume shallow reader nesting.
}
- rcu_read_unlock_trace_special(t, nesting);
+ WARN_ON_ONCE(nesting != 0);
+ rcu_read_unlock_trace_special(t);
}
void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 69d2d3346a3d..9f1b005afc9c 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -847,7 +847,7 @@ static void rcu_read_unlock_iw(struct irq_work *iwp)
static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
/* If we are the last reader, wake up the grace-period kthread. */
-void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
+void rcu_read_unlock_trace_special(struct task_struct *t)
{
int nq = READ_ONCE(t->trc_reader_special.b.need_qs);
@@ -857,7 +857,7 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting)
// Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
if (nq)
WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
- WRITE_ONCE(t->trc_reader_nesting, nesting);
+ WRITE_ONCE(t->trc_reader_nesting, 0);
if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
irq_work_queue(&rcu_tasks_trace_iw);
}
@@ -1199,7 +1199,7 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t)
WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
WRITE_ONCE(t->trc_reader_nesting, 0);
if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))
- rcu_read_unlock_trace_special(t, 0);
+ rcu_read_unlock_trace_special(t);
}
/**