rcu: Add synchronize_sched_expedited() rcutorture doc + updates

This patch updates the rcutorture documentation to include
updated output format.  It also brings the RCU documentation up
to date.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: akpm@linux-foundation.org
Cc: torvalds@linux-foundation.org
Cc: davem@davemloft.net
Cc: dada1@cosmosbay.com
Cc: zbr@ioremap.net
Cc: jeff.chua.linux@gmail.com
Cc: paulus@samba.org
Cc: laijs@cn.fujitsu.com
Cc: jengelh@medozas.de
Cc: r000n@r000n.net
Cc: benh@kernel.crashing.org
Cc: mathieu.desnoyers@polymtl.ca
LKML-Reference: <12459460983193-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 5 deletions

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index accfe2f5247d..51525a30e8b4 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -11,7 +11,10 @@ over a rather long period of time, but improvements are always welcome!
         structure is updated more than about 10% of the time, then
         you should strongly consider some other approach, unless
         detailed performance measurements show that RCU is nonetheless
-        the right tool for the job.
+        the right tool for the job.  Yes, you might think of RCU
+        as simply cutting overhead off of the readers and imposing it
+        on the writers.  That is exactly why normal uses of RCU will
+        do much more reading than updating.
 
         Another exception is where performance is not an issue, and RCU
         provides a simpler implementation.  An example of this situation
@@ -240,10 +243,11 @@ over a rather long period of time, but improvements are always welcome!
         instead need to use synchronize_irq() or synchronize_sched().
 
 12.     Any lock acquired by an RCU callback must be acquired elsewhere
-        with irq disabled, e.g., via spin_lock_irqsave().  Failing to
-        disable irq on a given acquisition of that lock will result in
-        deadlock as soon as the RCU callback happens to interrupt that
-        acquisition's critical section.
+        with softirq disabled, e.g., via spin_lock_irqsave(),
+        spin_lock_bh(), etc.  Failing to disable irq on a given
+        acquisition of that lock will result in deadlock as soon as the
+        RCU callback happens to interrupt that acquisition's critical
+        section.
 
 13.     RCU callbacks can be and are executed in parallel.  In many cases,
         the callback code simply wrappers around kfree(), so that this
@@ -310,3 +314,9 @@ over a rather long period of time, but improvements are always welcome!
         Because these primitives only wait for pre-existing readers,
         it is the caller's responsibility to guarantee safety to
         any subsequent readers.
+
+16.     The various RCU read-side primitives do -not- contain memory
+        barriers.  The CPU (and in some cases, the compiler) is free
+        to reorder code into and out of RCU read-side critical sections.
+        It is the responsibility of the RCU update-side primitives to
+        deal with this.