@@ -25,10 +25,10 @@ warnings:
- A CPU looping with bottom halves disabled.
-- For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the kernel
- without invoking schedule(). If the looping in the kernel is
- really expected and desirable behavior, you might need to add
- some calls to cond_resched().
+- For !CONFIG_PREEMPTION kernels, a CPU looping anywhere in the
+ kernel without potentially invoking schedule(). If the looping
+ in the kernel is really expected and desirable behavior, you
+ might need to add some calls to cond_resched().
- Booting Linux using a console connection that is too slow to
keep up with the boot-time console-message rate. For example,
@@ -108,16 +108,17 @@ warnings:
- A bug in the RCU implementation.
-- A hardware failure. This is quite unlikely, but has occurred
- at least once in real life. A CPU failed in a running system,
- becoming unresponsive, but not causing an immediate crash.
- This resulted in a series of RCU CPU stall warnings, eventually
- leading the realization that the CPU had failed.
+- A hardware failure. This is quite unlikely, but is not at all
+ uncommon in large datacenter. In one memorable case some decades
+ back, a CPU failed in a running system, becoming unresponsive,
+ but not causing an immediate crash. This resulted in a series
+ of RCU CPU stall warnings, eventually leading the realization
+ that the CPU had failed.
-The RCU, RCU-sched, and RCU-tasks implementations have CPU stall warning.
-Note that SRCU does *not* have CPU stall warnings. Please note that
-RCU only detects CPU stalls when there is a grace period in progress.
-No grace period, no CPU stall warnings.
+The RCU, RCU-sched, RCU-tasks, and RCU-tasks-trace implementations have
+CPU stall warning. Note that SRCU does *not* have CPU stall warnings.
+Please note that RCU only detects CPU stalls when there is a grace period
+in progress. No grace period, no CPU stall warnings.
To diagnose the cause of the stall, inspect the stack traces.
The offending function will usually be near the top of the stack.
@@ -205,16 +206,21 @@ RCU_STALL_RAT_DELAY
rcupdate.rcu_task_stall_timeout
-------------------------------
- This boot/sysfs parameter controls the RCU-tasks stall warning
- interval. A value of zero or less suppresses RCU-tasks stall
- warnings. A positive value sets the stall-warning interval
- in seconds. An RCU-tasks stall warning starts with the line:
+ This boot/sysfs parameter controls the RCU-tasks and
+ RCU-tasks-trace stall warning intervals. A value of zero or less
+ suppresses RCU-tasks stall warnings. A positive value sets the
+ stall-warning interval in seconds. An RCU-tasks stall warning
+ starts with the line:
INFO: rcu_tasks detected stalls on tasks:
And continues with the output of sched_show_task() for each
task stalling the current RCU-tasks grace period.
+ An RCU-tasks-trace stall warning starts (and continues) similarly:
+
+ INFO: rcu_tasks_trace detected stalls on tasks
+
Interpreting RCU's CPU Stall-Detector "Splats"
==============================================
@@ -248,7 +254,8 @@ dynticks counter, which will have an even-numbered value if the CPU
is in dyntick-idle mode and an odd-numbered value otherwise. The hex
number between the two "/"s is the value of the nesting, which will be
a small non-negative number if in the idle loop (as shown above) and a
-very large positive number otherwise.
+very large positive number otherwise. The number following the final
+"/" is the NMI nesting, which will be a small non-negative number.
The "softirq=" portion of the message tracks the number of RCU softirq
handlers that the stalled CPU has executed. The number before the "/"
This commit updates stallwarn.rst to reflect RCU additions and changes over the past few years. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> --- Documentation/RCU/stallwarn.rst | 43 +++++++++++++++++++-------------- 1 file changed, 25 insertions(+), 18 deletions(-)