The sparse-based checking for non-RCU accesses to RCU-protected pointers
has been around for a very long time, and it is now the only type of
sparse-based checking that is optional.  This commit therefore makes
it unconditional.
Reported-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>

The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b17 ("nohz_full: Add full-system-idle state machine"),
but has not been used.  This commit therefore removes it.

If it turns out to be needed later, this commit can always be reverted.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>

This commit classifies tail recursion as an alternative way to write
a loop, with similar limitations.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit documents the auto-expediting requirement satisfied by
commits 2da4b2a7 ("srcu: Expedite first synchronize_srcu() when idle")
and 22607d66 ("srcu: Specify auto-expedite holdoff time").
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: NDavid Rientjes <rientjes@google.com>

The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks.  This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>

The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter.  However, this check reduces
overhead only after a rare race condition, and increases complexity.  This
commit therefore removes the scan and the mechanism enabling the scan.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Reported-by: N"yangzc@uit.com.cn" <yangzc@uit.com.cn>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

When an RCU-protected pointer is fetched but never dereferenced
rcu_access_pointer() should be used in place of rcu_dereference().
This commit explicitly records this very fact in Documentation/
RCU/rcu_dereference.txt, in order to prevent the usage of
rcu_dereference() in comparisons.
Signed-off-by: NMichalis Kokologiannakis <mixaskok@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The rcu_assign_pointer() macro has changed over time, and the version
in Documentation/RCU/whatisRCU.txt has not kept up.  This commit brings
it into 2017, albeit in a simplified fashion.
Reported-by: NAndrea Parri <parri.andrea@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

These changes include lighter-weight expedited grace periods, the fact
that expedited grace periods and rcu_barrier() no longer block CPU
hotplug, some HTML font fixups, noting that rcu_barrier() need not wait
for a grace period (even if callbacks are posted), the fact that SRCU
read-side critical sections can be used from offline CPUs, and the fact
that SRCU now maintains per-CPU callback lists.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The rcu_segcblist data structure, which contains segmented lists
of RCU callbacks, was recently added.  This commit updates the
documentation accordingly.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit rearranges the Documentation/RCU/stallwarn.txt file to
put the list of issues that can cause RCU CPU stall warnings near
the beginning of the document.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds a description of how expedited grace periods operate
during the mid-boot "dead zone", which starts when the scheduler spawns
the first kthread and ends when all of RCU's kthreads have been spawned.
In short, before mid-boot, synchronous grace periods can be a no-op.
After the end of mid-boot, workqueues may be used.  During mid-boot,
the requesting task drivees the expedited grace period.

For more detail, see https://lwn.net/Articles/716148/.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit updates the "Early Boot" section of the RCU requirements
to describe how synchronous RCU grace periods are now legal throughout
the boot process.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Expedited grace periods no longer fall back to normal grace periods
in response to lock contention, given that expedited grace periods
now use the rcu_node tree so as to avoid contention.  This commit
therfore removes the expedited_normal counter.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

Now that quick-quiz answers are inline, there is no separate section
containing those answers.  This commit therefore removes the dangling
reference from the RCU data-structures design documentation.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

This commit adds design documentation for expedited grace periods.
This documentation is in HTML rather than the new documentation
format because (1) I have prototype documentation already in HTML,
and (2) Attempting to learn the new documentation format while
creating the design documentation seems likely to result in neither
happening in a timely fashion.

Once the design documentation is complete, we can start a conversion effort.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

deference should actually be dereference.
Signed-off-by: NPranith Kumar <bobby.prani@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Recent memory-model work deduces the relationships of RCU read-side
critical sections and grace periods based on the relationships of
accesses within a critical section and accesses preceding and following
the grace period.  This commit therefore adds this viewpoint.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

A good practice is to prefix the names of functions by the name
of the subsystem.

The kthread worker API is a mix of classic kthreads and workqueues.  Each
worker has a dedicated kthread.  It runs a generic function that process
queued works.  It is implemented as part of the kthread subsystem.

This patch renames the existing kthread worker API to use
the corresponding name from the workqueues API prefixed by
kthread_:

__init_kthread_worker()		-> __kthread_init_worker()
init_kthread_worker()		-> kthread_init_worker()
init_kthread_work()		-> kthread_init_work()
insert_kthread_work()		-> kthread_insert_work()
queue_kthread_work()		-> kthread_queue_work()
flush_kthread_work()		-> kthread_flush_work()
flush_kthread_worker()		-> kthread_flush_worker()

Note that the names of DEFINE_KTHREAD_WORK*() macros stay
as they are. It is common that the "DEFINE_" prefix has
precedence over the subsystem names.

Note that INIT() macros and init() functions use different
naming scheme. There is no good solution. There are several
reasons for this solution:

  + "init" in the function names stands for the verb "initialize"
    aka "initialize worker". While "INIT" in the macro names
    stands for the noun "INITIALIZER" aka "worker initializer".

  + INIT() macros are used only in DEFINE() macros

  + init() functions are used close to the other kthread()
    functions. It looks much better if all the functions
    use the same scheme.

  + There will be also kthread_destroy_worker() that will
    be used close to kthread_cancel_work(). It is related
    to the init() function. Again it looks better if all
    functions use the same naming scheme.

  + there are several precedents for such init() function
    names, e.g. amd_iommu_init_device(), free_area_init_node(),
    jump_label_init_type(),  regmap_init_mmio_clk(),

  + It is not an argument but it was inconsistent even before.

[arnd@arndb.de: fix linux-next merge conflict]
 Link: http://lkml.kernel.org/r/20160908135724.1311726-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/1470754545-17632-3-git-send-email-pmladek@suse.comSuggested-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There is an assertion in __call_rcu() that checks only the bottom
bit of the rcu_head pointer, rather than the bottom two (as might be
expected for 32-bit systems) or the bottom three (as might be expected
for 64-bit systems).  This choice might be a bit surprising in these days
of ubiquitous 32-bit and 64-bit systems.  This commit therefore records
the reason for this odd alignment check, namely that m68k guarantees
only two-byte alignment despite being a 32-bit architectures.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

CONFIG_RCU_TORTURE_TEST_RUNNABLE was removed by commit 4e9a073f
("torture: Remove CONFIG_RCU_TORTURE_TEST_RUNNABLE, simplify code"),
but the documentation was not updated accordingly.  This commit therefore
updates the documentation to reflect CONFIG_RCU_TORTURE_TEST_RUNNABLE's
removal and to add a description for the alternative module parameter.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Signed-off-by: NEric Engestrom <eric@engestrom.ch>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Reported-by: NJim Roskind <jar@roskind.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Reported-by: NJim Roskind <jar@roskind.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This fixes several spelling mistakes in the Documentation/ tree, which
are caught by checkpatch.pl's spell checking.
Signed-off-by: NKees Cook <keescook@chromium.org>
Reviewed-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

This commit adds documentation for RCU's major data structures,
including rcu_state, rcu_node, rcu_data, rcu_dynticks, and rcu_head.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Commit #cdacbe1f ("rcu: Add fastpath bypassing funnel locking")
turns out to be a pessimization at high load because it forces a tree
full of tasks to wait for an expedited grace period that they probably
do not need.  This commit therefore removes this optimization.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Although call_rcu()'s fastpath works just fine on an idle CPU,
some branches of the slowpath invoke the scheduler, which uses
RCU.  Therefore, this commit emphasizes the fact that call_rcu()
must not be invoked from an idle CPU.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit uses colors to obscure the quick-quiz answers, thus getting
rid of the .htmlx file.  Use your mouse to select the answer in order
to see the text.  Alternatively, use your favorite scripting language
to remove all occurences of "<font color="ffffff">" from the file.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit removes a cutesy cartoon and also a diagram that can
just as easily be represented by text.
Reported-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

There is already a blanket statement about no member of RCU's API
being legal from an offline CPU, but add an explicit note where it
states that it is illegal to invoke call_rcu() from an NMI handler.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds a Quick Quiz whose answer explains why the compiler
code reordering enabled by CONFIG_PREEMPT=n's empty rcu_read_lock()
and rcu_read_unlock() functions does not hinder RCU's ability to figure
out which RCU read-side critical sections have completed and not.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>