Commit df00ccca authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull RCU updates from Ingo Molnar:
 "The main changes in this cycle were:

   - documentation updates

   - miscellaneous fixes

   - minor reorganization of code

   - torture-test updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
  rcu: Correctly handle sparse possible cpus
  rcu: sysctl: Panic on RCU Stall
  rcu: Fix a typo in a comment
  rcu: Make call_rcu_tasks() tolerate first call with irqs disabled
  rcu: Disable TASKS_RCU for usermode Linux
  rcu: No ordering for rcu_assign_pointer() of NULL
  rcutorture: Fix error return code in rcu_perf_init()
  torture: Inflict default jitter
  rcuperf: Don't treat gp_exp mis-setting as a WARN
  rcutorture: Drop "-soundhw pcspkr" from x86 boot arguments
  rcutorture: Don't specify the cpu type of QEMU on PPC
  rcutorture: Make -soundhw a x86 specific option
  rcutorture: Use vmlinux as the fallback kernel image
  rcutorture/doc: Create initrd using dracut
  torture: Stop onoff task if there is only one cpu
  torture: Add starvation events to error summary
  torture:  Break online and offline functions out of torture_onoff()
  torture: Forgive lengthy trace dumps and preemption
  torture: Remove CONFIG_RCU_TORTURE_TEST_RUNNABLE, simplify code
  torture: Simplify code, eliminate RCU_PERF_TEST_RUNNABLE
  ...
parents dd950695 54d5f16e

Documentation/RCU/Design/Requirements/Requirements.html

+35 −0
Original line number Diff line number Diff line
@@ -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

Documentation/RCU/stallwarn.txt

+1 −1
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@@ -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:

Documentation/RCU/whatisRCU.txt

+3 −0
Original line number Diff line number Diff line
@@ -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?

Documentation/sysctl/kernel.txt

+12 −0
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@@ -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

include/linux/kernel.h

+1 −0
Original line number Diff line number Diff line
@@ -451,6 +451,7 @@ extern int panic_on_oops; 
extern int panic_on_unrecovered_nmi;

extern int panic_on_io_nmi;

extern int panic_on_warn;

extern int sysctl_panic_on_rcu_stall;

extern int sysctl_panic_on_stackoverflow;



extern bool crash_kexec_post_notifiers;

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