Merge branch 'for-mingo' of...

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

“lazy” 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>

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

 *

 * 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

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);

#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) \