rcu: Merge adjacent identical ifdefs

Two ifdefs in kernel/rcupdate.c now have identical conditions with
nothing between them, so the commit merges them into a single ifdef.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Shrink TINY_RCU by moving exit_rcu()

Now that TINY_PREEMPT_RCU is no more, exit_rcu() is always an empty
function.  But if TINY_RCU is going to have an empty function, it should
be in include/linux/rcutiny.h, where it does not bloat the kernel.
This commit therefore moves exit_rcu() out of kernel/rcupdate.c to
kernel/rcutree_plugin.h, and places a static inline empty function in
include/linux/rcutiny.h in order to shrink TINY_RCU a bit.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Simplify RCU_TINY RCU callback invocation

TINY_PREEMPT_RCU could use a kthread to handle RCU callback invocation,
which required an API to abstract kthread vs. softirq invocation.
Now that TINY_PREEMPT_RCU is no longer with us, this commit retires
this API in favor of direct use of the relevant softirq primitives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Remove rcu_preempt_check_callbacks()

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_check_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Remove rcu_preempt_remove_callbacks()

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_remove_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Remove TINY_PREEMPT_RCU

TINY_PREEMPT_RCU adds significant code and complexity, but does not
offer commensurate benefits.  People currently using TINY_PREEMPT_RCU
can get much better memory footprint with TINY_RCU, or, if they really
need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively
minor degradation in memory footprint.  Please note that this move
has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545)
and on LWN (http://lwn.net/Articles/541037/).

This commit therefore removes TINY_PREEMPT_RCU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ]
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Remove rcu_preempt_process_callbacks()

With the removal of CONFIG_TINY_PREEMPT_RCU, rcu_preempt_process_callbacks()
is now an empty function.  This commit therefore eliminates it by
inlining it.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Consolidate rcutiny_plugin.h ifdefs

This commit rearranges code in order to allow ifdefs to be consolidated
in kernel/rcutiny_plugin.h, simplifying the code.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
is disabled (which in turns disables detection of RCU CPU stalls).
This commit saves a few lines of source code by defining these functions
only if CONFIG_RCU_TRACE=y.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
rcu: Convert rcutree.c printk calls

This commit converts printk() calls to the corresponding pr_*() calls.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Move code to apply callback-numbering simplifications

The addition of callback numbering allows combining the detection of the
ends of old grace periods and the beginnings of new grace periods.  This
commit moves code to set the stage for this combining.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Make __note_new_gpnum() check for ends of prior grace periods

The current implementation can detect the beginning of a new grace period
before noting the end of a previous grace period.  Although the current
implementation correctly handles this sort of nonsense, it would be
good to reduce RCU's state space by making such nonsense unnecessary,
which is now possible thanks to the fact that RCU's callback groups are
now numbered.

This commit therefore makes __note_new_gpnum() invoke
__rcu_process_gp_end() in order to note the ends of prior grace
periods before noting the beginnings of new grace periods.
Of course, this now means that note_new_gpnum() notes both the
beginnings and ends of grace periods, and could therefore be
used in place of rcu_process_gp_end().  But that is a job for
later commits.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Rename note_new_gpnum() to note_gp_changes()

Because note_new_gpnum() now also checks for the ends of old grace periods,
this commit changes its name to note_gp_changes().  Later commits will merge
rcu_process_gp_end() into note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Switch callers from rcu_process_gp_end() to note_gp_changes()

Because note_gp_changes() now incorporates rcu_process_gp_end() function,
this commit switches to the former and eliminates the latter.  In
addition, this commit changes external calls from __rcu_process_gp_end()
to __note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Merge __rcu_process_gp_end() into __note_gp_changes()

This commit eliminates some duplicated code by merging
__rcu_process_gp_end() into __note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Eliminate check_for_new_grace_period() wrapper function

One of the calls to check_for_new_grace_period() is now redundant due to
an immediately preceding call to note_gp_changes().  Eliminating this
redundant call leaves a single caller, which is simpler if inlined.
This commit therefore eliminates the redundant call and inlines the
body of check_for_new_grace_period() into the single remaining call site.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Inline trivial wrapper function rcu_start_gp_per_cpu()

Given the changes that introduce note_gp_change(), rcu_start_gp_per_cpu()
is now a trivial wrapper function with only one caller.  This commit
therefore inlines it into its sole call site.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Move redundant call to note_gp_changes() into called function

The __rcu_process_callbacks() invokes note_gp_changes() immediately
before invoking rcu_check_quiescent_state(), which conditionally
invokes that same function.  This commit therefore eliminates the
call to note_gp_changes() in __rcu_process_callbacks() in favor of
making unconditional to call from rcu_check_quiescent_state() to
note_gp_changes().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
rcu: Drive quiescent-state-forcing delay from HZ

Systems with HZ=100 can have slow bootup times due to the default
three-jiffy delays between quiescent-state forcing attempts.  This
commit therefore auto-tunes the RCU_JIFFIES_TILL_FORCE_QS value based
on the value of HZ.  However, this would break very large systems that
require more time between quiescent-state forcing attempts.  This
commit therefore also ups the default delay by one jiffy for each
256 CPUs that might be on the system (based off of nr_cpu_ids at
runtime, -not- NR_CPUS at build time).

Updated to collapse #ifdefs for RCU_JIFFIES_TILL_FORCE_QS into a
step-function definition as suggested by Josh Triplett.

Reported-by: Paul Mackerras <paulus@au1.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
drivers: avoid parsing names as kthread_run() format strings

Calling kthread_run with a single name parameter causes it to be handled
as a format string. Many callers are passing potentially dynamic string
content, so use "%s" in those cases to avoid any potential accidents.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>