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-rw-r--r--Documentation/RCU/rcu_dereference.txt2
-rw-r--r--Documentation/RCU/stallwarn.txt29
-rw-r--r--Documentation/RCU/trace.txt36
-rw-r--r--Documentation/RCU/whatisRCU.txt2
4 files changed, 31 insertions, 38 deletions
diff --git a/Documentation/RCU/rcu_dereference.txt b/Documentation/RCU/rcu_dereference.txt
index 1e6c0da99..c0bf2441a 100644
--- a/Documentation/RCU/rcu_dereference.txt
+++ b/Documentation/RCU/rcu_dereference.txt
@@ -28,7 +28,7 @@ o You must use one of the rcu_dereference() family of primitives
o Avoid cancellation when using the "+" and "-" infix arithmetic
operators. For example, for a given variable "x", avoid
"(x-x)". There are similar arithmetic pitfalls from other
- arithmetic operatiors, such as "(x*0)", "(x/(x+1))" or "(x%1)".
+ arithmetic operators, such as "(x*0)", "(x/(x+1))" or "(x%1)".
The compiler is within its rights to substitute zero for all of
these expressions, so that subsequent accesses no longer depend
on the rcu_dereference(), again possibly resulting in bugs due
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index b57c0c1cd..efb945487 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -26,12 +26,6 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
Stall-warning messages may be enabled and disabled completely via
/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.
-CONFIG_RCU_CPU_STALL_INFO
-
- This kernel configuration parameter causes the stall warning to
- print out additional per-CPU diagnostic information, including
- information on scheduling-clock ticks and RCU's idle-CPU tracking.
-
RCU_STALL_DELAY_DELTA
Although the lockdep facility is extremely useful, it does add
@@ -101,15 +95,13 @@ interact. Please note that it is not possible to entirely eliminate this
sort of false positive without resorting to things like stop_machine(),
which is overkill for this sort of problem.
-If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
-more information is printed with the stall-warning message, for example:
+Recent kernels will print a long form of the stall-warning message:
INFO: rcu_preempt detected stall on CPU
0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543
(t=65000 jiffies)
-In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is
-printed:
+In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed:
INFO: rcu_preempt detected stall on CPU
0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D
@@ -171,6 +163,23 @@ message will be about three times the interval between the beginning
of the stall and the first message.
+Stall Warnings for Expedited Grace Periods
+
+If an expedited grace period detects a stall, it will place a message
+like the following in dmesg:
+
+ INFO: rcu_sched detected expedited stalls on CPUs: { 1 2 6 } 26009 jiffies s: 1043
+
+This indicates that CPUs 1, 2, and 6 have failed to respond to a
+reschedule IPI, that the expedited grace period has been going on for
+26,009 jiffies, and that the expedited grace-period sequence counter is
+1043. The fact that this last value is odd indicates that an expedited
+grace period is in flight.
+
+It is entirely possible to see stall warnings from normal and from
+expedited grace periods at about the same time from the same run.
+
+
What Causes RCU CPU Stall Warnings?
So your kernel printed an RCU CPU stall warning. The next question is
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 08651da15..97f17e9de 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -237,42 +237,26 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of
The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
-s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
+s=21872 wd0=0 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872
These fields are as follows:
-o "s" is the starting sequence number.
+o "s" is the sequence number, with an odd number indicating that
+ an expedited grace period is in progress.
-o "d" is the ending sequence number. When the starting and ending
- numbers differ, there is an expedited grace period in progress.
-
-o "w" is the number of times that the sequence numbers have been
- in danger of wrapping.
-
-o "tf" is the number of times that contention has resulted in a
- failure to begin an expedited grace period.
-
-o "wd1" and "wd2" are the number of times that an attempt to
- start an expedited grace period found that someone else had
- completed an expedited grace period that satisfies the
+o "wd0", "wd1", "wd2", and "wd3" are the number of times that an
+ attempt to start an expedited grace period found that someone
+ else had completed an expedited grace period that satisfies the
attempted request. "Our work is done."
-o "n" is number of times that contention was so great that
- the request was demoted from an expedited grace period to
- a normal grace period.
+o "n" is number of times that a concurrent CPU-hotplug operation
+ forced a fallback to a normal grace period.
+
+o "enq" is the number of quiescent states still outstanding.
o "sc" is the number of times that the attempt to start a
new expedited grace period succeeded.
-o "dt" is the number of times that we attempted to update
- the "d" counter.
-
-o "dl" is the number of times that we failed to update the "d"
- counter.
-
-o "dx" is the number of times that we succeeded in updating
- the "d" counter.
-
The output of "cat rcu/rcu_preempt/rcugp" looks as follows:
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 5746b0c77..adc218400 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -883,7 +883,7 @@ All: lockdep-checked RCU-protected pointer access
rcu_access_pointer
rcu_dereference_raw
- rcu_lockdep_assert
+ RCU_LOCKDEP_WARN
rcu_sleep_check
RCU_NONIDLE