Instead of creating a worker for each cwq and putting it into the
shared pool, manage per-cpu workers dynamically.
Works aren't supposed to be cpu cycle hogs and maintaining just enough
concurrency to prevent work processing from stalling due to lack of
processing context is optimal. gcwq keeps the number of concurrent
active workers to minimum but no less. As long as there's one or more
running workers on the cpu, no new worker is scheduled so that works
can be processed in batch as much as possible but when the last
running worker blocks, gcwq immediately schedules new worker so that
the cpu doesn't sit idle while there are works to be processed.
gcwq always keeps at least single idle worker around. When a new
worker is necessary and the worker is the last idle one, the worker
assumes the role of "manager" and manages the worker pool -
ie. creates another worker. Forward-progress is guaranteed by having
dedicated rescue workers for workqueues which may be necessary while
creating a new worker. When the manager is having problem creating a
new worker, mayday timer activates and rescue workers are summoned to
the cpu and execute works which might be necessary to create new
workers.
Trustee is expanded to serve the role of manager while a CPU is being
taken down and stays down. As no new works are supposed to be queued
on a dead cpu, it just needs to drain all the existing ones. Trustee
continues to try to create new workers and summon rescuers as long as
there are pending works. If the CPU is brought back up while the
trustee is still trying to drain the gcwq from the previous offlining,
the trustee will kill all idles ones and tell workers which are still
busy to rebind to the cpu, and pass control over to gcwq which assumes
the manager role as necessary.
Concurrency managed worker pool reduces the number of workers
drastically. Only workers which are necessary to keep the processing
going are created and kept. Also, it reduces cache footprint by
avoiding unnecessarily switching contexts between different workers.
Please note that this patch does not increase max_active of any
workqueue. All workqueues can still only process one work per cpu.
Signed-off-by: Tejun Heo <tj@kernel.org>
With gcwq managing all the workers and work->data pointing to the last
gcwq it was on, non-reentrance can be easily implemented by checking
whether the work is still running on the previous gcwq on queueing.
Implement it.
Signed-off-by: Tejun Heo <tj@kernel.org>
To implement non-reentrant workqueue, the last gcwq a work was
executed on must be reliably obtainable as long as the work structure
is valid even if the previous workqueue has been destroyed.
To achieve this, work->data will be overloaded to carry the last cpu
number once execution starts so that the previous gcwq can be located
reliably. This means that cwq can't be obtained from work after
execution starts but only gcwq.
Implement set_work_{cwq|cpu}(), get_work_[g]cwq() and
clear_work_data() to set work data to the cpu number when starting
execution, access the overloaded work data and clear it after
cancellation.
queue_delayed_work_on() is updated to preserve the last cpu while
in-flight in timer and other callers which depended on getting cwq
from work after execution starts are converted to depend on gcwq
instead.
* Anton Blanchard fixed compile error on powerpc due to missing
linux/threads.h include.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Anton Blanchard <anton@samba.org>
Reimplement st (single thread) workqueue so that it's friendly to
shared worker pool. It was originally implemented by confining st
workqueues to use cwq of a fixed cpu and always having a worker for
the cpu. This implementation isn't very friendly to shared worker
pool and suboptimal in that it ends up crossing cpu boundaries often.
Reimplement st workqueue using dynamic single cpu binding and
cwq->limit. WQ_SINGLE_THREAD is replaced with WQ_SINGLE_CPU. In a
single cpu workqueue, at most single cwq is bound to the wq at any
given time. Arbitration is done using atomic accesses to
wq->single_cpu when queueing a work. Once bound, the binding stays
till the workqueue is drained.
Note that the binding is never broken while a workqueue is frozen.
This is because idle cwqs may have works waiting in delayed_works
queue while frozen. On thaw, the cwq is restarted if there are any
delayed works or unbound otherwise.
When combined with max_active limit of 1, single cpu workqueue has
exactly the same execution properties as the original single thread
workqueue while allowing sharing of per-cpu workers.
Signed-off-by: Tejun Heo <tj@kernel.org>
Currently, workqueue freezing is implemented by marking the worker
freezeable and calling try_to_freeze() from dispatch loop.
Reimplement it using cwq->limit so that the workqueue is frozen
instead of the worker.
* workqueue_struct->saved_max_active is added which stores the
specified max_active on initialization.
* On freeze, all cwq->max_active's are quenched to zero. Freezing is
complete when nr_active on all cwqs reach zero.
* On thaw, all cwq->max_active's are restored to wq->saved_max_active
and the worklist is repopulated.
This new implementation allows having single shared pool of workers
per cpu.
Signed-off-by: Tejun Heo <tj@kernel.org>
Add cwq->nr_active, cwq->max_active and cwq->delayed_work. nr_active
counts the number of active works per cwq. A work is active if it's
flushable (colored) and is on cwq's worklist. If nr_active reaches
max_active, new works are queued on cwq->delayed_work and activated
later as works on the cwq complete and decrement nr_active.
cwq->max_active can be specified via the new @max_active parameter to
__create_workqueue() and is set to 1 for all workqueues for now. As
each cwq has only single worker now, this double queueing doesn't
cause any behavior difference visible to its users.
This will be used to reimplement freeze/thaw and implement shared
worker pool.
Signed-off-by: Tejun Heo <tj@kernel.org>
A work is linked to the next one by having WORK_STRUCT_LINKED bit set
and these links can be chained. When a linked work is dispatched to a
worker, all linked works are dispatched to the worker's newly added
->scheduled queue and processed back-to-back.
Currently, as there's only single worker per cwq, having linked works
doesn't make any visible behavior difference. This change is to
prepare for multiple shared workers per cpu.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reimplement workqueue flushing using color coded works. wq has the
current work color which is painted on the works being issued via
cwqs. Flushing a workqueue is achieved by advancing the current work
colors of cwqs and waiting for all the works which have any of the
previous colors to drain.
Currently there are 16 possible colors, one is reserved for no color
and 15 colors are useable allowing 14 concurrent flushes. When color
space gets full, flush attempts are batched up and processed together
when color frees up, so even with many concurrent flushers, the new
implementation won't build up huge queue of flushers which has to be
processed one after another.
Only works which are queued via __queue_work() are colored. Works
which are directly put on queue using insert_work() use NO_COLOR and
don't participate in workqueue flushing. Currently only works used
for work-specific flush fall in this category.
This new implementation leaves only cleanup_workqueue_thread() as the
user of flush_cpu_workqueue(). Just make its users use
flush_workqueue() and kthread_stop() directly and kill
cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier
request anymore, the comment describing the complex synchronization
around it in cleanup_workqueue_thread() is removed together with the
function.
This new implementation is to allow having and sharing multiple
workers per cpu.
Please note that one more bit is reserved for a future work flag by
this patch. This is to avoid shifting bits and updating comments
later.
Signed-off-by: Tejun Heo <tj@kernel.org>
work->data field is used for two purposes. It points to cwq it's
queued on and the lower bits are used for flags. Currently, two bits
are reserved which is always safe as 4 byte alignment is guaranteed on
every architecture. However, future changes will need more flag bits.
On SMP, the percpu allocator is capable of honoring larger alignment
(there are other users which depend on it) and larger alignment works
just fine. On UP, percpu allocator is a thin wrapper around
kzalloc/kfree() and don't honor alignment request.
This patch introduces WORK_STRUCT_FLAG_BITS and implements
alloc/free_cwqs() which guarantees max(1 << WORK_STRUCT_FLAG_BITS,
__alignof__(unsigned long long) alignment both on SMP and UP. On SMP,
simply wrapping percpu allocator is enough. On UP, extra space is
allocated so that cwq can be aligned and the original pointer can be
stored after it which is used in the free path.
* Alignment problem on UP is reported by Michal Simek.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Reported-by: Michal Simek <michal.simek@petalogix.com>
Work flags are about to see more traditional mask handling. Define
WORK_STRUCT_*_BIT as the bit position constant and redefine
WORK_STRUCT_* as bit masks. Also, make WORK_STRUCT_STATIC_* flags
conditional
While at it, re-define these constants as enums and use
WORK_STRUCT_STATIC instead of hard-coding 2 in
WORK_DATA_STATIC_INIT().
Signed-off-by: Tejun Heo <tj@kernel.org>
Currently, __create_workqueue_key() takes @singlethread and
@freezeable paramters and store them separately in workqueue_struct.
Merge them into a single flags parameter and field and use
WQ_FREEZEABLE and WQ_SINGLE_THREAD.
Signed-off-by: Tejun Heo <tj@kernel.org>
Make the following updates in preparation of concurrency managed
workqueue. None of these changes causes any visible behavior
difference.
* Add comments and adjust indentations to data structures and several
functions.
* Rename wq_per_cpu() to get_cwq() and swap the position of two
parameters for consistency. Convert a direct per_cpu_ptr() access
to wq->cpu_wq to get_cwq().
* Add work_static() and Update set_wq_data() such that it sets the
flags part to WORK_STRUCT_PENDING | WORK_STRUCT_STATIC if static |
@extra_flags.
* Move santiy check on work->entry emptiness from queue_work_on() to
__queue_work() which all queueing paths share.
* Make __queue_work() take @cpu and @wq instead of @cwq.
* Restructure flush_work() and __create_workqueue_key() to make them
easier to modify.
Signed-off-by: Tejun Heo <tj@kernel.org>
With stop_machine() converted to use cpu_stop, RT workqueue doesn't
have any user left. Kill RT workqueue support.
Signed-off-by: Tejun Heo <tj@kernel.org>
Some recent uses of RCU make use of workqueues. In these uses, execution
within the context of a specific workqueue takes the place of the usual
RCU read-side primitives such as rcu_read_lock(), and flushing of workqueues
takes the place of the usual RCU grace-period primitives. Checking for
correct use of rcu_dereference() in such cases requires a test of whether
the code is executing in the context of a particular workqueue. This
commit adds an in_workqueue_context() function that provides this test.
This new function is only defined when lockdep is enabled, which allows
it to be used as the second argument of rcu_dereference_check().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Add debugobject support to track the life time of work_structs.
While at it, remove duplicate definition of
INIT_DELAYED_WORK_ON_STACK().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
cancel_delayed_work() has to use del_timer_sync() to guarantee the timer
function is not running after return. But most users doesn't actually
need this, and del_timer_sync() has problems: it is not useable from
interrupt, and it depends on every lock which could be taken from irq.
Introduce __cancel_delayed_work() which calls del_timer() instead.
The immediate reason for this patch is
http://bugzilla.kernel.org/show_bug.cgi?id=13757
but hopefully this helper makes sense anyway.
As for 13757 bug, actually we need requeue_delayed_work(), but its
semantics are not yet clear.
Merge this patch early to resolves cross-tree interdependencies between
input and infiniband.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Roland Dreier <rdreier@cisco.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It is a fairly common operation to have a pointer to a work and to need a
pointer to the delayed work it is contained in. In particular, all
delayed works which want to rearm themselves will have to do that. So it
would seem fair to offer a helper function for this operation.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Greg KH <greg@kroah.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
debugobjects: add and use INIT_WORK_ON_STACK
rcu: remove duplicate CONFIG_RCU_CPU_STALL_DETECTOR
relay: fix lock imbalance in relay_late_setup_files
oprofile: fix uninitialized use of struct op_entry
rcu: move Kconfig menu
softlock: fix false panic which can occur if softlockup_thresh is reduced
rcu: add __cpuinit to rcu_init_percpu_data()
Impact: Fix debugobjects warning
debugobject enabled kernels spit out a warning in hpet code due to a
workqueue which is initialized on stack.
Add INIT_WORK_ON_STACK() which calls init_timer_on_stack() and use it
in hpet.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Alexander Beregalov reported that this warning is caused by the HPET code:
> hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0
> hpet0: 3 comparators, 64-bit 14.318180 MHz counter
> ODEBUG: object is on stack, but not annotated
> ------------[ cut here ]------------
> WARNING: at lib/debugobjects.c:251 __debug_object_init+0x2a4/0x352()
> Bisected down to 26afe5f2fb
> (x86: HPET_MSI Initialise per-cpu HPET timers)
The commit is fine - but the on-stack workqueue entry needs annotation.
Reported-and-bisected-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: introduce new APIs
We want to deprecate cpumasks on the stack, as we are headed for
gynormous numbers of CPUs. Eventually, we want to head towards an
undefined 'struct cpumask' so they can never be declared on stack.
1) New cpumask functions which take pointers instead of copies.
(cpus_* -> cpumask_*)
2) Several new helpers to reduce requirements for temporary cpumasks
(cpumask_first_and, cpumask_next_and, cpumask_any_and)
3) Helpers for declaring cpumasks on or offstack for large NR_CPUS
(cpumask_var_t, alloc_cpumask_var and free_cpumask_var)
4) 'struct cpumask' for explicitness and to mark new-style code.
5) Make iterator functions stop at nr_cpu_ids (a runtime constant),
not NR_CPUS for time efficiency and for smaller dynamic allocations
in future.
6) cpumask_copy() so we can allocate less than a full cpumask eventually
(for alloc_cpumask_var), and so we can eliminate the 'struct cpumask'
definition eventually.
7) work_on_cpu() helper for doing task on a CPU, rather than saving old
cpumask for current thread and manipulating it.
8) smp_call_function_many() which is smp_call_function_mask() except
taking a cpumask pointer.
Note that this patch simply introduces the new functions and leaves
the obsolescent ones in place. This is to simplify the transition
patches.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
create_rt_workqueue will create a real time prioritized workqueue.
This is needed for the conversion of stop_machine to a workqueue based
implementation.
This patch adds yet another parameter to __create_workqueue_key to tell
it that we want an rt workqueue.
However it looks like we rather should have something like "int type"
instead of singlethread, freezable and rt.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Most of users of flush_workqueue() can be changed to use cancel_work_sync(),
but sometimes we really need to wait for the completion and cancelling is not
an option. schedule_on_each_cpu() is good example.
Add the new helper, flush_work(work), which waits for the completion of the
specific work_struct. More precisely, it "flushes" the result of of the last
queue_work() which is visible to the caller.
For example, this code
queue_work(wq, work);
/* WINDOW */
queue_work(wq, work);
flush_work(work);
doesn't necessary work "as expected". What can happen in the WINDOW above is
- wq starts the execution of work->func()
- the caller migrates to another CPU
now, after the 2nd queue_work() this work is active on the previous CPU, and
at the same time it is queued on another. In this case flush_work(work) may
return before the first work->func() completes.
It is trivial to add another helper
int flush_work_sync(struct work_struct *work)
{
return flush_work(work) || wait_on_work(work);
}
which works "more correctly", but it has to iterate over all CPUs and thus
it much slower than flush_work().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Max Krasnyansky <maxk@qualcomm.com>
Acked-by: Jarek Poplawski <jarkao2@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This interface allows adding a job on a specific cpu.
Although a work struct on a cpu will be scheduled to other cpu if the cpu
dies, there is a recursion if a work task tries to offline the cpu it's
running on. we need to schedule the task to a specific cpu in this case.
http://bugzilla.kernel.org/show_bug.cgi?id=10897
[oleg@tv-sign.ru: cleanups]
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Rus <harbour@sfinx.od.ua>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
FASTCALL() is always expanded to empty, remove it.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Dave Young reported warnings from lockdep that the workqueue API
can sometimes try to register lockdep classes with the same key
but different names. This is not permitted in lockdep.
Unfortunately, I was unaware of that restriction when I wrote
the code to debug workqueue problems with lockdep and used the
workqueue name as the lockdep class name. This can obviously
lead to the problem if the workqueue name is dynamic.
This patch solves the problem by always using a constant name
for the workqueue's lockdep class, namely either the constant
name that was passed in or a string consisting of the variable
name.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
In the following scenario:
code path 1:
my_function() -> lock(L1); ...; flush_workqueue(); ...
code path 2:
run_workqueue() -> my_work() -> ...; lock(L1); ...
you can get a deadlock when my_work() is queued or running
but my_function() has acquired L1 already.
This patch adds a pseudo-lock to each workqueue to make lockdep
warn about this scenario.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change cancel_work_sync() and cancel_delayed_work_sync() to return a boolean
indicating whether the work was actually cancelled. A zero return value means
that the work was not pending/queued.
Without that kind of change it is not possible to avoid flush_workqueue()
sometimes, see the next patch as an example.
Also, this patch unifies both functions and kills the (unlikely) busy-wait
loop.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Imho, the current naming of cancel_xxx workqueue functions is very confusing.
cancel_delayed_work()
cancel_rearming_delayed_work()
cancel_rearming_delayed_workqueue() // obsolete
cancel_work_sync()
This looks as if the first 2 functions differ in "type" of their argument
which is not true any longer, nowadays the difference is the behaviour.
The semantics of cancel_rearming_delayed_work(dwork) was changed
significantly, it doesn't require that dwork rearms itself, and cancels dwork
synchronously.
Rename it to cancel_delayed_work_sync(). This matches cancel_delayed_work()
and cancel_work_sync(). Re-create cancel_rearming_delayed_work() as a simple
inline obsolete wrapper, like cancel_rearming_delayed_workqueue().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Jarek Poplawski <jarkao2@o2.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
As pointed out by Jarek Poplawski, the patch
[WORKQUEUE]: cancel_delayed_work: use del_timer() instead of del_timer_sync()
commit: 071b638689
was wrong, it was merged by mistake after that.
From the changelog:
after this patch:
...
delayed_work_timer_fn->__queue_work() in progress.
The latter doesn't differ from the caller's POV,
it does make a difference if the caller calls flush_workqueue() after
cancel_delayed_work(), in that case flush_workqueue() can miss this
work_struct.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Jarek Poplawski <jarkao2@o2.pl>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It is a known fact that freezeable multithreaded workqueues doesn't like
CPU_DEAD. We keep them only for the incoming CPU-hotplug rework.
Sadly, we can't just kill create_freezeable_workqueue() right now, make
them singlethread.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
flush_work(wq, work) doesn't need the first parameter, we can use cwq->wq
(this was possible from the very beginnig, I missed this). So we can unify
flush_work_keventd and flush_work.
Also, rename flush_work() to cancel_work_sync() and fix all callers.
Perhaps this is not the best name, but "flush_work" is really bad.
(akpm: this is why the earlier patches bypassed maintainers)
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Auke Kok <auke-jan.h.kok@intel.com>,
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We don't have any users, and it is not so trivial to use NOAUTOREL works
correctly. It is better to simplify API.
Delete NOAUTOREL support and rename work_release to work_clear_pending to
avoid a confusion.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cancel_rearming_delayed_workqueue(wq, dwork) doesn't need the first
parameter. We don't hang on un-queued dwork any longer, and work->data
doesn't change its type. This means we can always figure out "wq" from
dwork when it is needed.
Remove this parameter, and rename the function to
cancel_rearming_delayed_work(). Re-create an inline "obsolete"
cancel_rearming_delayed_workqueue(wq) which just calls
cancel_rearming_delayed_work().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Because it has no callers.
Actually, I think the whole idea of run_scheduled_work() was not right, not
good to mix "unqueue this work and execute its ->func()" in one function.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
A basic problem with flush_scheduled_work() is that it blocks behind _all_
presently-queued works, rather than just the work whcih the caller wants to
flush. If the caller holds some lock, and if one of the queued work happens
to want that lock as well then accidental deadlocks can occur.
One example of this is the phy layer: it wants to flush work while holding
rtnl_lock(). But if a linkwatch event happens to be queued, the phy code will
deadlock because the linkwatch callback function takes rtnl_lock.
So we implement a new function which will flush a *single* work - just the one
which the caller wants to free up. Thus we avoid the accidental deadlocks
which can arise from unrelated subsystems' callbacks taking shared locks.
flush_work() non-blockingly dequeues the work_struct which we want to kill,
then it waits for its handler to complete on all CPUs.
Add ->current_work to the "struct cpu_workqueue_struct", it points to
currently running "struct work_struct". When flush_work(work) detects
->current_work == work, it inserts a barrier at the _head_ of ->worklist
(and thus right _after_ that work) and waits for completition. This means
that the next work fired on that CPU will be this barrier, or another
barrier queued by concurrent flush_work(), so the caller of flush_work()
will be woken before any "regular" work has a chance to run.
When wait_on_work() unlocks workqueue_mutex (or whatever we choose to protect
against CPU hotplug), CPU may go away. But in that case take_over_work() will
move a barrier we queued to another CPU, it will be fired sometime, and
wait_on_work() will be woken.
Actually, we are doing cleanup_workqueue_thread()->kthread_stop() before
take_over_work(), so cwq->thread should complete its ->worklist (and thus
the barrier), because currently we don't check kthread_should_stop() in
run_workqueue(). But even if we did, everything should be ok.
[akpm@osdl.org: cleanup]
[akpm@osdl.org: add flush_work_keventd() wrapper]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add a new deferrable delayed work init. This can be used to schedule work
that are 'unimportant' when CPU is idle and can be called later, when CPU
eventually comes out of idle.
Use this init in cpufreq ondemand governor.
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
del_timer_sync() buys nothing for cancel_delayed_work(), but it is less
efficient since it locks the timer unconditionally, and may wait for the
completion of the delayed_work_timer_fn().
cancel_delayed_work() == 0 means:
before this patch:
work->func may still be running or queued
after this patch:
work->func may still be running or queued, or
delayed_work_timer_fn->__queue_work() in progress.
The latter doesn't differ from the caller's POV,
delayed_work_timer_fn() is called with _PENDING
bit set.
cancel_delayed_work() == 1 with this patch adds a new possibility:
delayed_work->work was cancelled, but delayed_work_timer_fn
is still running (this is only possible for the re-arming
works on single-threaded workqueue).
In this case the timer was re-started by work->func(), nobody
else can do this. This in turn means that delayed_work_timer_fn
has already passed __queue_work() (and wont't touch delayed_work)
because nobody else can queue delayed_work->work.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
On architectures where the atomicity of the bit operations is handled by
external means (ie a separate spinlock to protect concurrent accesses),
just doing a direct assignment on the workqueue data field (as done by
commit 4594bf159f) can cause the
assignment to be lost due to lack of serialization with the bitops on
the same word.
So we need to serialize the assignment with the locks on those
architectures (notably older ARM chips, PA-RISC and sparc32).
So rather than using an "unsigned long", let's use "atomic_long_t",
which already has a safe assignment operation (atomic_long_set()) on
such architectures.
This requires that the atomic operations use the same atomicity locks as
the bit operations do, but that is largely the case anyway. Sparc32
will probably need fixing.
Architectures (including modern ARM with LL/SC) that implement sane
atomic operations for SMP won't see any of this matter.
Cc: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: David Miller <davem@davemloft.com>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Linux Arch Maintainers <linux-arch@vger.kernel.org>
Cc: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Nobody uses it, but it was still wrong. Using the macro argument name
'work' meant that when we used 'work' as a member name, that would also
get replaced by the macro argument.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This allows workqueue users to run just their own pending work, rather
than wait for the whole workqueue to finish running. This solves the
deadlock with networking libphy that was due to other workqueue entries
possibly needing a lock that was held by the routine that wanted to
flush its own work.
It's not wonderful: if you absolutely need to synchronize with the work
function having been executed, any user strictly speaking should have
its own completion tracking logic, since when we run things explicitly
by hand, the generic workqueue layer can no longer help us synchronize.
Also, this is strictly only usable for work that has been scheduled
without any delayed timers. You can not mix the new interface with
schedule_delayed_work().
But it's better than what we had currently.
Acked-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Make it possible to create a workqueue the worker thread of which will be
frozen during suspend, along with other kernel threads.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Nigel Cunningham <nigel@suspend2.net>
Cc: David Chinner <dgc@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.
For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.
To make this work, an extra flag is introduced into the management side of the
work_struct. This governs auto-release of the structure upon execution.
Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function. This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated.. This is a
problem if the auxiliary data is taken away (as done by the last patch).
However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems. But then the work function must itself release the
work_struct by calling work_release().
In most cases, automatic release is fine, so this is the default. Special
initiators exist for the non-auto-release case (ending in _NAR).
Signed-Off-By: David Howells <dhowells@redhat.com>
Reclaim a word from the size of the work_struct by folding the pending bit and
the wq_data pointer together. This shouldn't cause misalignment problems as
all pointers should be at least 4-byte aligned.
Signed-Off-By: David Howells <dhowells@redhat.com>
Define a type for the work function prototype. It's not only kept in the
work_struct struct, it's also passed as an argument to several functions.
This makes it easier to change it.
Signed-Off-By: David Howells <dhowells@redhat.com>
Separate delayable work items from non-delayable work items be splitting them
into a separate structure (delayed_work), which incorporates a work_struct and
the timer_list removed from work_struct.
The work_struct struct is huge, and this limits it's usefulness. On a 64-bit
architecture it's nearly 100 bytes in size. This reduces that by half for the
non-delayable type of event.
Signed-Off-By: David Howells <dhowells@redhat.com>
We have several points in the SCSI stack (primarily for our device
functions) where we need to guarantee process context, but (given the
place where the last reference was released) we cannot guarantee this.
This API gets around the issue by executing the function directly if
the caller has process context, but scheduling a workqueue to execute
in process context if the caller doesn't have it.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
swap migration's isolate_lru_page() currently uses an IPI to notify other
processors that the lru caches need to be drained if the page cannot be
found on the LRU. The IPI interrupt may interrupt a processor that is just
processing lru requests and cause a race condition.
This patch introduces a new function run_on_each_cpu() that uses the
keventd() to run the LRU draining on each processor. Processors disable
preemption when dealing the LRU caches (these are per processor) and thus
executing LRU draining from another process is safe.
Thanks to Lee Schermerhorn <lee.schermerhorn@hp.com> for finding this race
condition.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This was unexported by Arjan because we have no current users.
However, during a conversion from tasklets to workqueues of the parisc led
functions, we ran across a case where this was needed. In particular, the
open coded equivalent of cancel_rearming_delayed_workqueue was implemented
incorrectly, which is, I think, all the evidence necessary that this is a
useful API.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Tejun Heo