From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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,
dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
bobby.prani@gmail.com,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 08/10] documentation: Sharpen up the no-readers quick quiz
Date: Tue, 12 Apr 2016 08:18:19 -0700 [thread overview]
Message-ID: <1460474301-22998-8-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20160412151755.GA22416@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
Documentation/RCU/Design/Requirements/Requirements.html | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index acdad96f78e9..85cf2238fd08 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -1002,18 +1002,21 @@ obligation to wait for these new readers.
<tr><th> </th></tr>
<tr><th align="left">Quick Quiz:</th></tr>
<tr><td>
- Suppose that synchronize_rcu() did wait until all readers had completed.
- Would the updater be able to rely on this?
+ Suppose that synchronize_rcu() did wait until <i>all</i>
+ readers had completed instead of waiting only on
+ pre-existing readers.
+ For how long would the updater be able to rely on there
+ being no readers?
</td></tr>
<tr><th align="left">Answer:</th></tr>
<tr><td bgcolor="#ffffff"><font color="ffffff">
- No.
+ For no time at all.
Even if <tt>synchronize_rcu()</tt> were to wait until
all readers had completed, a new reader might start immediately after
<tt>synchronize_rcu()</tt> completed.
Therefore, the code following
- <tt>synchronize_rcu()</tt> cannot rely on there being no readers
- in any case.
+ <tt>synchronize_rcu()</tt> can <i>never</i> rely on there being
+ no readers.
</font></td></tr>
<tr><td> </td></tr>
</table>
--
2.5.2
next prev parent reply other threads:[~2016-04-12 15:18 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-12 15:17 [PATCH tip/core/rcu 0/10] Documentation updates for 4.7 Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 01/10] documentation: Make sample code and documentation consistent Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 02/10] documentation: Add real-time requirements from CPU-bound workloads Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 03/10] documentation: Add synchronize_rcu_mult() to the requirements Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 04/10] documentation: Explain why rcu_read_lock() needs no barrier() Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 05/10] documentation: Document illegality of call_rcu() from offline CPUs Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 06/10] documentation: Remove unnecessary images from requirements Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 07/10] documentation: Get rid of duplicate .htmlx file Paul E. McKenney
2016-04-12 15:18 ` Paul E. McKenney [this message]
2016-04-12 15:18 ` [PATCH tip/core/rcu 09/10] documentation: Emphasize the call_rcu() is illegal from idle Paul E. McKenney
2016-04-12 15:18 ` [PATCH tip/core/rcu 10/10] documentation: Add documentation for RCU's major data structures Paul E. McKenney
2016-04-16 14:52 ` Boqun Feng
2016-04-17 2:33 ` Paul E. McKenney
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