Commit 4b978934 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:

   - Expedited grace-period changes, most notably avoiding having user
     threads drive expedited grace periods, using a workqueue instead.

   - Miscellaneous fixes, including a performance fix for lists that was
     sent with the lists modifications.

   - CPU hotplug updates, most notably providing exact CPU-online
     tracking for RCU. This will in turn allow removal of the checks
     supporting RCU's prior heuristic that was based on the assumption
     that CPUs would take no longer than one jiffy to come online.

   - Torture-test updates.

   - Documentation updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (22 commits)
  list: Expand list_first_entry_or_null()
  torture: TOROUT_STRING(): Insert a space between flag and message
  rcuperf: Consistently insert space between flag and message
  rcutorture: Print out barrier error as document says
  torture: Add task state to writer-task stall printk()s
  torture: Convert torture_shutdown() to hrtimer
  rcutorture: Convert to hotplug state machine
  cpu/hotplug: Get rid of CPU_STARTING reference
  rcu: Provide exact CPU-online tracking for RCU
  rcu: Avoid redundant quiescent-state chasing
  rcu: Don't use modular infrastructure in non-modular code
  sched: Make wake_up_nohz_cpu() handle CPUs going offline
  rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads
  rcu: Use RCU's online-CPU state for expedited IPI retry
  rcu: Exclude RCU-offline CPUs from expedited grace periods
  rcu: Make expedited RCU CPU stall warnings respond to controls
  rcu: Stop disabling expedited RCU CPU stall warnings
  rcu: Drive expedited grace periods from workqueue
  rcu: Consolidate expedited grace period machinery
  documentation: Record reason for rcu_head two-byte alignment
  ...
parents 72a9cdd0 2d8fbcd1

Documentation/RCU/Design/Requirements/Requirements.html

+22 −0
Original line number Diff line number Diff line
@@ -2493,6 +2493,28 @@ or some future “lazy” 
variant of <tt>call_rcu()</tt> that might one day be created for

energy-efficiency purposes.



<p>

That said, there are limits.

RCU requires that the <tt>rcu_head</tt> structure be aligned to a

two-byte boundary, and passing a misaligned <tt>rcu_head</tt>

structure to one of the <tt>call_rcu()</tt> family of functions

will result in a splat.

It is therefore necessary to exercise caution when packing

structures containing fields of type <tt>rcu_head</tt>.

Why not a four-byte or even eight-byte alignment requirement?

Because the m68k architecture provides only two-byte alignment,

and thus acts as alignment's least common denominator.



<p>

The reason for reserving the bottom bit of pointers to

<tt>rcu_head</tt> structures is to leave the door open to

&ldquo;lazy&rdquo; callbacks whose invocations can safely be deferred.

Deferring invocation could potentially have energy-efficiency

benefits, but only if the rate of non-lazy callbacks decreases

significantly for some important workload.

In the meantime, reserving the bottom bit keeps this option open

in case it one day becomes useful.



<h3><a name="Performance, Scalability, Response Time, and Reliability">

Performance, Scalability, Response Time, and Reliability</a></h3>

Documentation/RCU/torture.txt

+0 −15
Original line number Diff line number Diff line
@@ -10,21 +10,6 @@ status messages via printk(), which can be examined via the dmesg 
command (perhaps grepping for "torture").  The test is started

when the module is loaded, and stops when the module is unloaded.



CONFIG_RCU_TORTURE_TEST_RUNNABLE



It is also possible to specify CONFIG_RCU_TORTURE_TEST=y, which will

result in the tests being loaded into the base kernel.  In this case,

the CONFIG_RCU_TORTURE_TEST_RUNNABLE config option is used to specify

whether the RCU torture tests are to be started immediately during

boot or whether the /proc/sys/kernel/rcutorture_runnable file is used

to enable them.  This /proc file can be used to repeatedly pause and

restart the tests, regardless of the initial state specified by the

CONFIG_RCU_TORTURE_TEST_RUNNABLE config option.



You will normally -not- want to start the RCU torture tests during boot

(and thus the default is CONFIG_RCU_TORTURE_TEST_RUNNABLE=n), but doing

this can sometimes be useful in finding boot-time bugs.





MODULE PARAMETERS

include/linux/list.h

+5 −2
Original line number Diff line number Diff line
@@ -381,8 +381,11 @@ static inline void list_splice_tail_init(struct list_head *list, 
 *

 * Note that if the list is empty, it returns NULL.

 */

#define list_first_entry_or_null(ptr, type, member) \

	(!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)

#define list_first_entry_or_null(ptr, type, member) ({ \

	struct list_head *head__ = (ptr); \

	struct list_head *pos__ = READ_ONCE(head__->next); \

	pos__ != head__ ? list_entry(pos__, type, member) : NULL; \

})



/**

 * list_next_entry - get the next element in list

include/linux/rcupdate.h

+1 −0
Original line number Diff line number Diff line
@@ -334,6 +334,7 @@ void rcu_sched_qs(void); 
void rcu_bh_qs(void);

void rcu_check_callbacks(int user);

void rcu_report_dead(unsigned int cpu);

void rcu_cpu_starting(unsigned int cpu);



#ifndef CONFIG_TINY_RCU

void rcu_end_inkernel_boot(void);

include/linux/torture.h

+1 −1
Original line number Diff line number Diff line
@@ -43,7 +43,7 @@ 


#define TORTURE_FLAG "-torture:"

#define TOROUT_STRING(s) \

	pr_alert("%s" TORTURE_FLAG s "\n", torture_type)

	pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s)

#define VERBOSE_TOROUT_STRING(s) \

	do { if (verbose) pr_alert("%s" TORTURE_FLAG " %s\n", torture_type, s); } while (0)

#define VERBOSE_TOROUT_ERRSTRING(s) \

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