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authorIngo Molnar <mingo@kernel.org>2016-06-30 09:27:41 +0300
committerIngo Molnar <mingo@kernel.org>2016-06-30 09:27:41 +0300
commit54d5f16e55a7cdd64e0f6bcadf2b5f871f94bb83 (patch)
tree169537619e16c6a6d802585ba97aae405642233a /Documentation
parent4c2e07c6a29e0129e975727b9f57eede813eea85 (diff)
parent4d03754f04247bc4d469b78b61cac942df37445d (diff)
downloadlinux-54d5f16e55a7cdd64e0f6bcadf2b5f871f94bb83.tar.xz
Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu
Pull RCU changes from Paul E. McKenney: - Documentation updates. Just some simple changes, no design-level additions. - Miscellaneous fixes. - Torture-test updates. Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/RCU/Design/Requirements/Requirements.html35
-rw-r--r--Documentation/RCU/stallwarn.txt2
-rw-r--r--Documentation/RCU/whatisRCU.txt3
-rw-r--r--Documentation/sysctl/kernel.txt12
4 files changed, 51 insertions, 1 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index e7e24b3e86e2..ece410f40436 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2391,6 +2391,41 @@ and <tt>RCU_NONIDLE()</tt> on the other while inspecting
idle-loop code.
Steven Rostedt supplied <tt>_rcuidle</tt> event tracing,
which is used quite heavily in the idle loop.
+However, there are some restrictions on the code placed within
+<tt>RCU_NONIDLE()</tt>:
+
+<ol>
+<li> Blocking is prohibited.
+ In practice, this is not a serious restriction given that idle
+ tasks are prohibited from blocking to begin with.
+<li> Although nesting <tt>RCU_NONIDLE()</tt> is permited, they cannot
+ nest indefinitely deeply.
+ However, given that they can be nested on the order of a million
+ deep, even on 32-bit systems, this should not be a serious
+ restriction.
+ This nesting limit would probably be reached long after the
+ compiler OOMed or the stack overflowed.
+<li> Any code path that enters <tt>RCU_NONIDLE()</tt> must sequence
+ out of that same <tt>RCU_NONIDLE()</tt>.
+ For example, the following is grossly illegal:
+
+ <blockquote>
+ <pre>
+ 1 RCU_NONIDLE({
+ 2 do_something();
+ 3 goto bad_idea; /* BUG!!! */
+ 4 do_something_else();});
+ 5 bad_idea:
+ </pre>
+ </blockquote>
+
+ <p>
+ It is just as illegal to transfer control into the middle of
+ <tt>RCU_NONIDLE()</tt>'s argument.
+ Yes, in theory, you could transfer in as long as you also
+ transferred out, but in practice you could also expect to get sharply
+ worded review comments.
+</ol>
<p>
It is similarly socially unacceptable to interrupt an
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 0f7fb4298e7e..e93d04133fe7 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -49,7 +49,7 @@ 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 jiffies. An RCU-tasks stall warning starts wtih the line:
+ in jiffies. An RCU-tasks stall warning starts with the line:
INFO: rcu_tasks detected stalls on tasks:
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 111770ffa10e..204422719197 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -5,6 +5,9 @@ to start learning about RCU:
2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/
3. RCU part 3: the RCU API http://lwn.net/Articles/264090/
4. The RCU API, 2010 Edition http://lwn.net/Articles/418853/
+ 2010 Big API Table http://lwn.net/Articles/419086/
+5. The RCU API, 2014 Edition http://lwn.net/Articles/609904/
+ 2014 Big API Table http://lwn.net/Articles/609973/
What is RCU?
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index a3683ce2a2f3..33204604de6c 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -58,6 +58,7 @@ show up in /proc/sys/kernel:
- panic_on_stackoverflow
- panic_on_unrecovered_nmi
- panic_on_warn
+- panic_on_rcu_stall
- perf_cpu_time_max_percent
- perf_event_paranoid
- perf_event_max_stack
@@ -618,6 +619,17 @@ a kernel rebuild when attempting to kdump at the location of a WARN().
==============================================================
+panic_on_rcu_stall:
+
+When set to 1, calls panic() after RCU stall detection messages. This
+is useful to define the root cause of RCU stalls using a vmcore.
+
+0: do not panic() when RCU stall takes place, default behavior.
+
+1: panic() after printing RCU stall messages.
+
+==============================================================
+
perf_cpu_time_max_percent:
Hints to the kernel how much CPU time it should be allowed to