path: root/Documentation/RCU
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-23 16:34:02 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-23 16:34:02 -0700
commit2c96c7751d2bb822542b03ddfaca70933f5aaf02 (patch)
tree9bdb922d816db6bcfdc92e048167007af9006df0 /Documentation/RCU
parenta6b9b4d50f492630443b38404d1f436b3b748c14 (diff)
rcu: upgrade stallwarn.txt documentation for CPU-bound RT processes
CPU-bound real-time processes can cause RCU CPU stall warnings, and much other trouble as well. Document the fact that they can cause RCU CPU stall warnings. Suggested-by: Darren Hart <dvhltc@us.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 44c6dcc93d6d..862c08ef1fde 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -80,6 +80,24 @@ o A CPU looping with bottom halves disabled. This condition can
o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
without invoking schedule().
+o A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might
+ happen to preempt a low-priority task in the middle of an RCU
+ read-side critical section. This is especially damaging if
+ that low-priority task is not permitted to run on any other CPU,
+ in which case the next RCU grace period can never complete, which
+ will eventually cause the system to run out of memory and hang.
+ While the system is in the process of running itself out of
+ memory, you might see stall-warning messages.
+o A CPU-bound real-time task in a CONFIG_PREEMPT_RT kernel that
+ is running at a higher priority than the RCU softirq threads.
+ This will prevent RCU callbacks from ever being invoked,
+ and in a CONFIG_TREE_PREEMPT_RCU kernel will further prevent
+ RCU grace periods from ever completing. Either way, the
+ system will eventually run out of memory and hang. In the
+ CONFIG_TREE_PREEMPT_RCU case, you might see stall-warning
+ messages.
o A bug in the RCU implementation.
o A hardware failure. This is quite unlikely, but has occurred

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