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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-08-03 19:41:23 -0400
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-09-23 10:42:23 -0400
commit2aef619c7524d73d18ff7b102a1706066b69141d (patch)
treeda1409acbdc4baca4858af9fbc7e413fd5efa0d0 /Documentation/RCU
parent13dbf9140c726c307a9c7e2b7ff83cf95da3bb44 (diff)
rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits
The current documentation did not help someone grepping for SRCU to learn that disabling preemption is not a replacement for srcu_read_lock(), so upgrade the documentation to bring this out, not just for SRCU, but also for RCU-bh. Also document the fact that SRCU readers are respected on CPUs executing in user mode, idle CPUs, and even on offline CPUs. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/checklist.txt6
-rw-r--r--Documentation/RCU/whatisRCU.txt9
2 files changed, 13 insertions, 2 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index fc103d7a0474..cdb20d41a44a 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -310,6 +310,12 @@ over a rather long period of time, but improvements are always welcome!
310 code under the influence of preempt_disable(), you instead 310 code under the influence of preempt_disable(), you instead
311 need to use synchronize_irq() or synchronize_sched(). 311 need to use synchronize_irq() or synchronize_sched().
312 312
313 This same limitation also applies to synchronize_rcu_bh()
314 and synchronize_srcu(), as well as to the asynchronous and
315 expedited forms of the three primitives, namely call_rcu(),
316 call_rcu_bh(), call_srcu(), synchronize_rcu_expedited(),
317 synchronize_rcu_bh_expedited(), and synchronize_srcu_expedited().
318
31312. Any lock acquired by an RCU callback must be acquired elsewhere 31912. Any lock acquired by an RCU callback must be acquired elsewhere
314 with softirq disabled, e.g., via spin_lock_irqsave(), 320 with softirq disabled, e.g., via spin_lock_irqsave(),
315 spin_lock_bh(), etc. Failing to disable irq on a given 321 spin_lock_bh(), etc. Failing to disable irq on a given
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 69ee188515e7..bf0f6de2aa00 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -873,7 +873,7 @@ d. Do you need to treat NMI handlers, hardirq handlers,
873 and code segments with preemption disabled (whether 873 and code segments with preemption disabled (whether
874 via preempt_disable(), local_irq_save(), local_bh_disable(), 874 via preempt_disable(), local_irq_save(), local_bh_disable(),
875 or some other mechanism) as if they were explicit RCU readers? 875 or some other mechanism) as if they were explicit RCU readers?
876 If so, you need RCU-sched. 876 If so, RCU-sched is the only choice that will work for you.
877 877
878e. Do you need RCU grace periods to complete even in the face 878e. Do you need RCU grace periods to complete even in the face
879 of softirq monopolization of one or more of the CPUs? For 879 of softirq monopolization of one or more of the CPUs? For
@@ -884,7 +884,12 @@ f. Is your workload too update-intensive for normal use of
884 RCU, but inappropriate for other synchronization mechanisms? 884 RCU, but inappropriate for other synchronization mechanisms?
885 If so, consider SLAB_DESTROY_BY_RCU. But please be careful! 885 If so, consider SLAB_DESTROY_BY_RCU. But please be careful!
886 886
887g. Otherwise, use RCU. 887g. Do you need read-side critical sections that are respected
888 even though they are in the middle of the idle loop, during
889 user-mode execution, or on an offlined CPU? If so, SRCU is the
890 only choice that will work for you.
891
892h. Otherwise, use RCU.
888 893
889Of course, this all assumes that you have determined that RCU is in fact 894Of course, this all assumes that you have determined that RCU is in fact
890the right tool for your job. 895the right tool for your job.