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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-08-23 23:34:02 (GMT) |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2010-08-23 23:34:02 (GMT) |
commit | 2c96c7751d2bb822542b03ddfaca70933f5aaf02 (patch) | |
tree | 9bdb922d816db6bcfdc92e048167007af9006df0 /Documentation | |
parent | a6b9b4d50f492630443b38404d1f436b3b748c14 (diff) | |
download | linux-2c96c7751d2bb822542b03ddfaca70933f5aaf02.tar.xz |
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')
-rw-r--r-- | Documentation/RCU/stallwarn.txt | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 44c6dcc9..862c08e 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 |