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Message-Id: <1460474301-22998-8-git-send-email-paulmck@linux.vnet.ibm.com> Date: Tue, 12 Apr 2016 08:18:19 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH tip/core/rcu 08/10] documentation: Sharpen up the no-readers quick quiz Signed-off-by: Paul E. McKenney <paulmck@...ux.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
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