Currently, destroy_workqueue() makes the workqueue deny all new
queueing by setting WQ_DYING and flushes the workqueue once before
proceeding with destruction; however, there are cases where work items
queue more related work items.  Currently, such users need to
explicitly flush the workqueue multiple times depending on the
possible depth of such chained queueing.

This patch updates the queueing path such that a work item can queue
further work items on the same workqueue even when WQ_DYING is set.
The flush on destruction is automatically retried until the workqueue
is empty.  This guarantees that the workqueue is empty on destruction
while allowing chained queueing.

The flush retry logic whines if it takes too many retries to drain the
workqueue.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>

Running the annotate branch profiler on three boxes, including my
main box that runs firefox, evolution, xchat, and is part of the distcc farm,
showed this with the likelys in the workqueue code:

 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
      96   996253  99 wq_worker_sleeping             workqueue.c          703
      96   996247  99 wq_worker_waking_up            workqueue.c          677

The likely()s in this case were assuming that WORKER_NOT_RUNNING will
most likely be false. But this is not the case. The reason is
(and shown by adding trace_printks and testing it) that most of the time
WORKER_PREP is set.

In worker_thread() we have:

	worker_clr_flags(worker, WORKER_PREP);

	[ do work stuff ]

	worker_set_flags(worker, WORKER_PREP, false);

(that 'false' means not to wake up an idle worker)

The wq_worker_sleeping() is called from schedule when a worker thread
is putting itself to sleep. Which happens most of the time outside
of that [ do work stuff ].

The wq_worker_waking_up is called by the wakeup worker code, which
is also callod outside that [ do work stuff ].

Thus, the likely and unlikely used by those two functions are actually
backwards.

Remove the annotation and let gcc figure it out.
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NTejun Heo <tj@kernel.org>

I found a trivial bug on initialization of workqueue.
Current init_workqueues doesn't check the result of
allocation of system_unbound_wq, this should be checked
like other queues.
Signed-off-by: NHitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Silly though it is, completions and wait_queue_heads use foo_ONSTACK
(COMPLETION_INITIALIZER_ONSTACK, DECLARE_COMPLETION_ONSTACK,
__WAIT_QUEUE_HEAD_INIT_ONSTACK and DECLARE_WAIT_QUEUE_HEAD_ONSTACK) so I
guess workqueues should do the same thing.

s/INIT_WORK_ON_STACK/INIT_WORK_ONSTACK/
s/INIT_DELAYED_WORK_ON_STACK/INIT_DELAYED_WORK_ONSTACK/

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In the MN10300 arch, we occasionally see an assertion being tripped in
alloc_cwqs() at the following line:

        /* just in case, make sure it's actually aligned */
  --->  BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
        return wq->cpu_wq.v ? 0 : -ENOMEM;

The values are:

        wa->cpu_wq.v => 0x902776e0
        align => 0x100

and align is calculated by the following:

        const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
                                   __alignof__(unsigned long long));

This is because the pointer in question (wq->cpu_wq.v) loses some of its
lower bits to control flags, and so the object it points to must be
sufficiently aligned to avoid the need to use those bits for pointing to
things.

Currently, 4 control bits and 4 colour bits are used in normal
circumstances, plus a debugging bit if debugging is set.  This requires
the cpu_workqueue_struct struct to be at least 256 bytes aligned (or 512
bytes aligned with debugging).

PERCPU() alignment on MN13000, however, is only 32 bytes as set in
vmlinux.lds.S.  So we set this to PAGE_SIZE (4096) to match most other
arches and stick a comment in alloc_cwqs() for anyone else who triggers
the assertion.
Reported-by: NAkira Takeuchi <takeuchi.akr@jp.panasonic.com>
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Acked-by: NMark Salter <msalter@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit a25909a4 (lockdep: Add an in_workqueue_context() lockdep-based
test function) added in_workqueue_context() but there hasn't been any
in-kernel user and the lockdep annotation in workqueue is scheduled to
change.  Remove the unused function.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

The documentation for schedule_on_each_cpu() states that it calls a
function on each online CPU from keventd.  This can easily be
interpreted as an asyncronous call because the description does not
mention that flush_work is called.  Clarify that it is synchronous.

tj: rephrased a bit
Signed-off-by: NMel Gorman <mel@csn.ul.ie>
Reviewed-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Add WQ_MEM_RECLAIM flag which currently maps to WQ_RESCUER, mark
WQ_RESCUER as internal and replace all external WQ_RESCUER usages to
WQ_MEM_RECLAIM.

This makes the API users express the intent of the workqueue instead
of indicating the internal mechanism used to guarantee forward
progress.  This is also to make it cleaner to add more semantics to
WQ_MEM_RECLAIM.  For example, if deemed necessary, memory reclaim
workqueues can be made highpri.

This patch doesn't introduce any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>

The policy function keep_working() didn't check GCWQ_HIGHPRI_PENDING
and could return %false with highpri work pending.  This could lead to
late execution of a highpri work which was delayed due to @max_active
throttling if other works are actively consuming CPU cycles.

For example, the following could happen.

1. Work W0 which burns CPU cycles.

2. Two works W1 and W2 are queued to a highpri wq w/ @max_active of 1.

3. W1 starts executing and W2 is put to delayed queue.  W0 and W1 are
   both runnable.

4. W1 finishes which puts W2 to pending queue but keep_working()
   incorrectly returns %false and the worker goes to sleep.

5. W0 finishes and W2 starts execution.

With this patch applied, W2 starts execution as soon as W1 finishes.
Signed-off-by: NTejun Heo <tj@kernel.org>

These two tracepoints allow tracking when and how a work is queued and
activated.  This patch is based on Frederic's patch to add queue_work
trace point.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>

Define workqueue_work event class and use it for workqueue_execute_end
trace point.  Also, move trace/events/workqueue.h include downwards
such that all struct definitions are visible to it.  This is to
prepare for more tracepoints and doesn't cause any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>

Implement flush[_delayed]_work_sync().  These are flush functions
which also make sure no CPU is still executing the target work from
earlier queueing instances.  These are similar to
cancel[_delayed]_work_sync() except that the target work item is
flushed instead of cancelled.
Signed-off-by: NTejun Heo <tj@kernel.org>

Factor out start_flush_work() from flush_work().  start_flush_work()
has @wait_executing argument which controls whether the barrier is
queued only if the work is pending or also if executing.  As
flush_work() needs to wait for execution too, it uses %true.

This commit doesn't cause any behavior difference.  start_flush_work()
will be used to implement flush_work_sync().
Signed-off-by: NTejun Heo <tj@kernel.org>

Make the following cleanup changes.

* Relocate flush/cancel function prototypes and definitions.

* Relocate wait_on_cpu_work() and wait_on_work() before
  try_to_grab_pending().  These will be used to implement
  flush_work_sync().

* Make all flush/cancel functions return bool instead of int.

* Update wait_on_cpu_work() and wait_on_work() to return %true if they
  actually waited.

* Add / update comments.

This patch doesn't cause any functional changes.
Signed-off-by: NTejun Heo <tj@kernel.org>

Update copyright notice and add Documentation/workqueue.txt.

Randy Dunlap, Dave Chinner: misc fixes.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-By: NFlorian Mickler <florian@mickler.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>

alloc_mayday_mask() was using alloc_cpumask_var() making
gcwq->mayday_mask contain garbage after initialization on
CONFIG_CPUMASK_OFFSTACK=y configurations.  This combined with the
previously fixed GCWQ_DISASSOCIATED initialization bug could make
rescuers fall into infinite loop trying to bind to an offline cpu.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NCAI Qian <caiqian@redhat.com>

init_workqueues() incorrectly marks workqueues for all possible CPUs
associated.  Combined with mayday_mask initialization bug, this can
make rescuers keep trying to bind to an offline gcwq indefinitely.
Fix init_workqueues() such that only online CPUs have their gcwqs have
GCWQ_DISASSOCIATED cleared.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NCAI Qian <caiqian@redhat.com>

cwq->nr_active is used to keep track of how many work items are active
for the cpu workqueue, where 'active' is defined as either pending on
global worklist or executing.  This is used to implement the
max_active limit and workqueue freezing.  If a work item is queued
after nr_active has already reached max_active, the work item doesn't
increment nr_active and is put on the delayed queue and gets activated
later as previous active work items retire.

try_to_grab_pending() which is used in the cancellation path
unconditionally decremented nr_active whether the work item being
cancelled is currently active or delayed, so cancelling a delayed work
item makes nr_active underflow.  This breaks max_active enforcement
and triggers BUG_ON() in destroy_workqueue() later on.

This patch fixes this bug by adding a flag WORK_STRUCT_DELAYED, which
is set while a work item in on the delayed list and making
try_to_grab_pending() decrement nr_active iff the work item is
currently active.

The addition of the flag enlarges cwq alignment to 256 bytes which is
getting a bit too large.  It's scheduled to be reduced back to 128
bytes by merging WORK_STRUCT_PENDING and WORK_STRUCT_CWQ in the next
devel cycle.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NJohannes Berg <johannes@sipsolutions.net>

Now that the worklist is global, having works pending after wq
destruction can easily lead to oops and destroy_workqueue() have
several BUG_ON()s to catch these cases.  Unfortunately, BUG_ON()
doesn't tell much about how the work became pending after the final
flush_workqueue().

This patch adds WQ_DYING which is set before the final flush begins.
If a work is requested to be queued on a dying workqueue,
WARN_ON_ONCE() is triggered and the request is ignored.  This clearly
indicates which caller is trying to queue a work on a dying workqueue
and keeps the system working in most cases.

Locking rule comment is updated such that the 'I' rule includes
modifying the field from destruction path.
Signed-off-by: NTejun Heo <tj@kernel.org>

worker_maybe_bind_and_lock() actually grabs gcwq->lock but was missing proper
annotation. Add it. So this patch will remove following sparse warnings:

 kernel/workqueue.c:1214:13: warning: context imbalance in 'worker_maybe_bind_and_lock' - wrong count at exit
 arch/x86/include/asm/irqflags.h:44:9: warning: context imbalance in 'worker_rebind_fn' - unexpected unlock
 kernel/workqueue.c:1991:17: warning: context imbalance in 'rescuer_thread' - unexpected unlock
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Some of internal functions called within gcwq->lock context releases and
regrabs the lock but were missing proper annotations. Add it.
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

With the introduction of the new unified work queue thread pools,
we lost one feature: It's no longer possible to know which worker
is causing the CPU to wake out of idle. The result is that PowerTOP
now reports a lot of "kworker/a:b" instead of more readable results.

This patch adds a pair of tracepoints to the new workqueue code,
similar in style to the timer/hrtimer tracepoints.

With this pair of tracepoints, the next PowerTOP can correctly
report which work item caused the wakeup (and how long it took):

Interrupt (43)            i915      time   3.51ms    wakeups 141
Work      ieee80211_iface_work      time   0.81ms    wakeups  29
Work              do_dbs_timer      time   0.55ms    wakeups  24
Process                   Xorg      time  21.36ms    wakeups   4
Timer    sched_rt_period_timer      time   0.01ms    wakeups   1
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

wq->rescuer is not freed when wq is destroyed, leads a memory leak
then. This patch also remove a redundant line.
Signed-off-by: NXiaotian Feng <dfeng@redhat.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>

Commit 6ee0578b (workqueue: mark init_workqueues as early_initcall)
made workqueue SMP initialization depend on workqueue_cpu_callback(),
which however was registered as hotcpu_notifier() and didn't get
called if CONFIG_HOTPLUG_CPU is not set.  This made gcwqs on non-boot
CPUs not create their initial workers leading to boot failures.  Fix
it by making it a cpu_notifier.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-and-bisected-by: Nwalt <w41ter@gmail.com>
Tested-by: NMarkus Trippelsdorf <markus@trippelsdorf.de>

works in schecule_on_each_cpu() is a percpu pointer but was missing
__percpu markup.  Add it.
Signed-off-by: NNamhyung Kim <namhyung@gmail.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

Mark init_workqueues() as early_initcall() and thus it will be initialized
before smp bringup. init_workqueues() registers for the hotcpu notifier
and thus it should cope with the processors that are brought online after
the workqueues are initialized.

x86 smp bringup code uses workqueues and uses a workaround for the
cold boot process (as the workqueues are initialized post smp_init()).
Marking init_workqueues() as early_initcall() will pave the way for
cleaning up this code.
Signed-off-by: NSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

for_each_*cwq_cpu() are similar to regular CPU iterators except that
it also considers the pseudo CPU number used for unbound workqueues.
Explain them.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

Once a work starts execution, its data contains the cpu number it was
on instead of pointing to cwq.  This is added by commit 7a22ad75
(workqueue: carry cpu number in work data once execution starts) to
reliably determine the work was last on even if the workqueue itself
was destroyed inbetween.

Whether data points to a cwq or contains a cpu number was
distinguished by comparing the value against PAGE_OFFSET.  The
assumption was that a cpu number should be below PAGE_OFFSET while a
pointer to cwq should be above it.  However, on architectures which
use separate address spaces for user and kernel spaces, this doesn't
hold as PAGE_OFFSET is zero.

Fix it by using an explicit flag, WORK_STRUCT_CWQ, to mark what the
data field contains.  If the flag is set, it's pointing to a cwq;
otherwise, it contains a cpu number.

Reported on s390 and microblaze during linux-next testing.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NSachin Sant <sachinp@in.ibm.com>
Reported-by: NMichal Simek <michal.simek@petalogix.com>
Reported-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Tested-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Tested-by: NMichal Simek <monstr@monstr.eu>

All cpumasks are assumed to have cpu 0 permanently set on UP, so it
can't be used to signify whether there's something to be done for the
CPU.  workqueue was using cpumask to track which CPU requested rescuer
assistance and this led rescuer thread to think there always are
pending mayday requests on UP, which resulted in infinite busy loops.

This patch fixes the problem by introducing mayday_mask_t and
associated helpers which wrap cpumask on SMP and emulates its behavior
using bitops and unsigned long on UP.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>

Commit f3421797 (workqueue: implement unbound workqueue) incorrectly
tested CONFIG_SMP as part of a C expression in alloc/free_cwqs().  As
CONFIG_SMP is not defined in UP, this breaks build.  Fix it by using

Found during linux-next build test.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>

maybe_create_worker() mismanaged locking when worker creation fails
and it has to retry.  Fix locking and simplify lock manipulation.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NYong Zhang <yong.zhang@windriver.com>

WQ_SINGLE_CPU combined with @max_active of 1 is used to achieve full
ordering among works queued to a workqueue.  The same can be achieved
using WQ_UNBOUND as unbound workqueues always use the gcwq for
WORK_CPU_UNBOUND.  As @max_active is always one and benefits from cpu
locality isn't accessible anyway, serving them with unbound workqueues
should be fine.

Drop WQ_SINGLE_CPU support and use WQ_UNBOUND instead.  Note that most
single thread workqueue users will be converted to use multithread or
non-reentrant instead and only the ones which require strict ordering
will keep using WQ_UNBOUND + @max_active of 1.
Signed-off-by: NTejun Heo <tj@kernel.org>

This patch implements unbound workqueue which can be specified with
WQ_UNBOUND flag on creation.  An unbound workqueue has the following
properties.

* It uses a dedicated gcwq with a pseudo CPU number WORK_CPU_UNBOUND.
  This gcwq is always online and disassociated.

* Workers are not bound to any CPU and not concurrency managed.  Works
  are dispatched to workers as soon as possible and the only applied
  limitation is @max_active.  IOW, all unbound workqeueues are
  implicitly high priority.

Unbound workqueues can be used as simple execution context provider.
Contexts unbound to any cpu are served as soon as possible.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Howells <dhowells@redhat.com>

In preparation of WQ_UNBOUND addition, make the following changes.

* Add WORK_CPU_* constants for pseudo cpu id numbers used (currently
  only WORK_CPU_NONE) and use them instead of NR_CPUS.  This is to
  allow another pseudo cpu id for unbound cpu.

* Reorder WQ_* flags.

* Make workqueue_struct->cpu_wq a union which contains a percpu
  pointer, regular pointer and an unsigned long value and use
  kzalloc/kfree() in UP allocation path.  This will be used to
  implement unbound workqueues which will use only one cwq on SMPs.

* Move alloc_cwqs() allocation after initialization of wq fields, so
  that alloc_cwqs() has access to wq->flags.

* Trivial relocation of wq local variables in freeze functions.

These changes don't cause any functional change.
Signed-off-by: NTejun Heo <tj@kernel.org>

When there's no pending work to do, worker_thread() goes back to sleep
after waking up without checking whether worker management is
necessary.  This means that idle worker exit requests can be ignored
if the gcwq stays empty.

Fix it by making worker_thread() always check whether worker
management is necessary before going to sleep.
Signed-off-by: NTejun Heo <tj@kernel.org>

get_work_gcwq() was incorrectly triggering BUG_ON() if cpu number is
equal to or higher than num_possible_cpus() instead of nr_cpu_ids.
Fix it.
Signed-off-by: NTejun Heo <tj@kernel.org>

When one flusher is cascading to the next flusher, it first sets
wq->first_flusher to the next one and sets up the next flush cycle.
If there's nothing to do for the next cycle, it clears
wq->flush_flusher and proceeds to the one after that.

If the woken up flusher checks wq->first_flusher before it gets
cleared, it will incorrectly assume the role of the first flusher,
which triggers BUG_ON() sanity check.

Fix it by checking wq->first_flusher again after grabbing the mutex.
Signed-off-by: NTejun Heo <tj@kernel.org>

worker_set/clr_flags() assume that if none of NOT_RUNNING flags is set
the worker must be contributing to nr_running which is only true if
the worker is actually running.

As when called from self, it is guaranteed that the worker is running,
those functions can be safely used from the worker itself and they
aren't necessary from other places anyway.  Make the following changes
to fix the bug.

* Make worker_set/clr_flags() whine if not called from self.

* Convert all places which called those functions from other tasks to
  manipulate flags directly.

* Make trustee_thread() directly clear nr_running after setting
  WORKER_ROGUE on all workers.  This is the only place where
  nr_running manipulation is necessary outside of workers themselves.

* While at it, add sanity check for nr_running in worker_enter_idle().
Signed-off-by: NTejun Heo <tj@kernel.org>

This patch implements cpu intensive workqueue which can be specified
with WQ_CPU_INTENSIVE flag on creation.  Works queued to a cpu
intensive workqueue don't participate in concurrency management.  IOW,
it doesn't contribute to gcwq->nr_running and thus doesn't delay
excution of other works.

Note that although cpu intensive works won't delay other works, they
can be delayed by other works.  Combine with WQ_HIGHPRI to avoid being
delayed by other works too.

As the name suggests this is useful when using workqueue for cpu
intensive works.  Workers executing cpu intensive works are not
considered for workqueue concurrency management and left for the
scheduler to manage.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>

This patch implements high priority workqueue which can be specified
with WQ_HIGHPRI flag on creation.  A high priority workqueue has the
following properties.

* A work queued to it is queued at the head of the worklist of the
  respective gcwq after other highpri works, while normal works are
  always appended at the end.

* As long as there are highpri works on gcwq->worklist,
  [__]need_more_worker() remains %true and process_one_work() wakes up
  another worker before it start executing a work.

The above two properties guarantee that works queued to high priority
workqueues are dispatched to workers and start execution as soon as
possible regardless of the state of other works.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Morton <akpm@linux-foundation.org>