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From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 10/13] rcu-tasks: Clarify read side section info for rcu_tasks_rude GP primitives
Date: Wed, 15 Sep 2021 16:46:01 -0700	[thread overview]
Message-ID: <20210915234604.3907802-10-paulmck@kernel.org> (raw)
In-Reply-To: <20210915234538.GA3907674@paulmck-ThinkPad-P17-Gen-1>

From: Neeraj Upadhyay <neeraju@codeaurora.org>

RCU tasks rude variant does not check whether the current
running context on a CPU is usermode. Read side critical section ends
on transition to usermode execution, by the virtue of usermode
execution being schedulable. Clarify this in comments for
call_rcu_tasks_rude() and synchronize_rcu_tasks_rude().

Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tasks.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index af7388849bed..8c63b4d23829 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -677,11 +677,11 @@ DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude,
  * period elapses, in other words after all currently executing RCU
  * read-side critical sections have completed. call_rcu_tasks_rude()
  * assumes that the read-side critical sections end at context switch,
- * cond_resched_rcu_qs(), or transition to usermode execution.  As such,
- * there are no read-side primitives analogous to rcu_read_lock() and
- * rcu_read_unlock() because this primitive is intended to determine
- * that all tasks have passed through a safe state, not so much for
- * data-structure synchronization.
+ * cond_resched_rcu_qs(), or transition to usermode execution (as
+ * usermode execution is schedulable). As such, there are no read-side
+ * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
+ * this primitive is intended to determine that all tasks have passed
+ * through a safe state, not so much for data-structure synchronization.
  *
  * See the description of call_rcu() for more detailed information on
  * memory ordering guarantees.
@@ -699,8 +699,8 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks_rude);
  * grace period has elapsed, in other words after all currently
  * executing rcu-tasks read-side critical sections have elapsed.  These
  * read-side critical sections are delimited by calls to schedule(),
- * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory,
- * anyway) cond_resched().
+ * cond_resched_tasks_rcu_qs(), userspace execution (which is a schedulable
+ * context), and (in theory, anyway) cond_resched().
  *
  * This is a very specialized primitive, intended only for a few uses in
  * tracing and other situations requiring manipulation of function preambles
-- 
2.31.1.189.g2e36527f23


  parent reply	other threads:[~2021-09-15 23:46 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-15 23:45 [PATCH rcu 0/13] Tasks RCU updates for v5.16 Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 01/13] rcu-tasks: Wait for trc_read_check_handler() IPIs Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 02/13] rcu-tasks: Simplify trc_read_check_handler() atomic operations Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 03/13] rcu-tasks: Add trc_inspect_reader() checks for exiting critical section Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 04/13] rcu-tasks: Remove second argument of rcu_read_unlock_trace_special() Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 05/13] rcu-tasks: Fix s/instruction/instructions/ typo in comment Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 06/13] rcu-tasks: Move RTGS_WAIT_CBS to beginning of rcu_tasks_kthread() loop Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 07/13] rcu-tasks: Fix s/rcu_add_holdout/trc_add_holdout/ typo in comment Paul E. McKenney
2021-09-15 23:45 ` [PATCH rcu 08/13] rcu-tasks: Correct firstreport usage in check_all_holdout_tasks_trace Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 09/13] rcu-tasks: Correct comparisons for CPU numbers in show_stalled_task_trace Paul E. McKenney
2021-09-15 23:46 ` Paul E. McKenney [this message]
2021-09-15 23:46 ` [PATCH rcu 11/13] rcu-tasks: Fix read-side primitives comment for call_rcu_tasks_trace Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 12/13] rcu-tasks: Fix IPI failure handling in trc_wait_for_one_reader Paul E. McKenney
2021-09-15 23:46 ` [PATCH rcu 13/13] rcu-tasks: Update comments to cond_resched_tasks_rcu_qs() Paul E. McKenney

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