async: Use a dedicated unbound workqueue with raised min_active

Async can schedule a number of interdependent work items. However, since
5797b1c18919 ("workqueue: Implement system-wide nr_active enf

async: Use a dedicated unbound workqueue with raised min_active

Async can schedule a number of interdependent work items. However, since
5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for
unbound workqueues"), unbound workqueues have separate min_active which sets
the number of interdependent work items that can be handled. This default
value is 8 which isn't sufficient for async and can lead to stalls during
resume from suspend in some cases.

Let's use a dedicated unbound workqueue with raised min_active.

Link: http://lkml.kernel.org/r/[email protected]
Reported-by: Marek Szyprowski <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

show more ...

async: Introduce async_schedule_dev_nocall()

In preparation for subsequent changes, introduce a specialized variant
of async_schedule_dev() that will not invoke the argument function
synchronously w

async: Introduce async_schedule_dev_nocall()

In preparation for subsequent changes, introduce a specialized variant
of async_schedule_dev() that will not invoke the argument function
synchronously when it cannot be scheduled for asynchronous execution.

The new function, async_schedule_dev_nocall(), will be used for fixing
possible deadlocks in the system-wide power management core code.

Signed-off-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Stanislaw Gruszka <[email protected]> for the series.
Tested-by: Youngmin Nam <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>

show more ...

async: Split async_schedule_node_domain()

In preparation for subsequent changes, split async_schedule_node_domain()
in two pieces so as to allow the bottom part of it to be called from a
somewhat di

async: Split async_schedule_node_domain()

In preparation for subsequent changes, split async_schedule_node_domain()
in two pieces so as to allow the bottom part of it to be called from a
somewhat different code path.

No functional impact.

Signed-off-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Stanislaw Gruszka <[email protected]>
Tested-by: Youngmin Nam <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>

show more ...

sched.h: move pid helpers to pid.h

This is needed for killing the sched.h dependency on rcupdate.h, and
pid.h is a better place for this code anyways.

Signed-off-by: Kent Overstreet <kent.overstree

sched.h: move pid helpers to pid.h

This is needed for killing the sched.h dependency on rcupdate.h, and
pid.h is a better place for this code anyways.

Signed-off-by: Kent Overstreet <[email protected]>

show more ...

Revert "module, async: async_synchronize_full() on module init iff async is used"

This reverts commit 774a1221e862b343388347bac9b318767336b20b.

We need to finish all async code before the module in

Revert "module, async: async_synchronize_full() on module init iff async is used"

This reverts commit 774a1221e862b343388347bac9b318767336b20b.

We need to finish all async code before the module init sequence is
done. In the reverted commit the PF_USED_ASYNC flag was added to mark a
thread that called async_schedule(). Then the PF_USED_ASYNC flag was
used to determine whether or not async_synchronize_full() needs to be
invoked. This works when modprobe thread is calling async_schedule(),
but it does not work if module dispatches init code to a worker thread
which then calls async_schedule().

For example, PCI driver probing is invoked from a worker thread based on
a node where device is attached:

if (cpu < nr_cpu_ids)
error = work_on_cpu(cpu, local_pci_probe, &ddi);
else
error = local_pci_probe(&ddi);

We end up in a situation where a worker thread gets the PF_USED_ASYNC
flag set instead of the modprobe thread. As a result,
async_synchronize_full() is not invoked and modprobe completes without
waiting for the async code to finish.

The issue was discovered while loading the pm80xx driver:
(scsi_mod.scan=async)

modprobe pm80xx worker
...
do_init_module()
...
pci_call_probe()
work_on_cpu(local_pci_probe)
local_pci_probe()
pm8001_pci_probe()
scsi_scan_host()
async_schedule()
worker->flags |= PF_USED_ASYNC;
...
< return from worker >
...
if (current->flags & PF_USED_ASYNC) <--- false
async_synchronize_full();

Commit 21c3c5d28007 ("block: don't request module during elevator init")
fixed the deadlock issue which the reverted commit 774a1221e862
("module, async: async_synchronize_full() on module init iff async is
used") tried to fix.

Since commit 0fdff3ec6d87 ("async, kmod: warn on synchronous
request_module() from async workers") synchronous module loading from
async is not allowed.

Given that the original deadlock issue is fixed and it is no longer
allowed to call synchronous request_module() from async we can remove
PF_USED_ASYNC flag to make module init consistently invoke
async_synchronize_full() unless async module probe is requested.

Signed-off-by: Igor Pylypiv <[email protected]>
Reviewed-by: Changyuan Lyu <[email protected]>
Reviewed-by: Luis Chamberlain <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

kernel/async.c: remove async_unregister_domain()

No callers in the tree.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rasmus Villemoes <linux@ras

kernel/async.c: remove async_unregister_domain()

No callers in the tree.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rasmus Villemoes <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

kernel/async.c: stop guarding pr_debug() statements

It's currently nigh impossible to get these pr_debug()s to print
something. Being guarded by initcall_debug means one has to enable tons
of other

kernel/async.c: stop guarding pr_debug() statements

It's currently nigh impossible to get these pr_debug()s to print
something. Being guarded by initcall_debug means one has to enable tons
of other debug output during boot, and the system_state condition further
means it's impossible to get them when loading modules later.

Also, the compiler can't know that these global conditions do not change,
so there are W=2 warnings

kernel/async.c:125:9: warning: `calltime' may be used uninitialized in this function [-Wmaybe-uninitialized]
kernel/async.c:300:9: warning: `starttime' may be used uninitialized in this function [-Wmaybe-uninitialized]

Make it possible, for a DYNAMIC_DEBUG kernel, to get these to print their
messages by booting with appropriate 'dyndbg="file async.c +p"' command
line argument. For a non-DYNAMIC_DEBUG kernel, pr_debug() compiles to
nothing.

This does cost doing an unconditional ktime_get() for the starttime value,
but the corresponding ktime_get for the end time can be elided by
factoring it into a function which only gets called if the printk()
arguments end up being evaluated.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rasmus Villemoes <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

kernel/async.c: fix pr_debug statement

An async_func_t returns void - any errors encountered it has to stash
somewhere for consumers to discover later.

Link: https://lkml.kernel.org/r/2021022612435

kernel/async.c: fix pr_debug statement

An async_func_t returns void - any errors encountered it has to stash
somewhere for consumers to discover later.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rasmus Villemoes <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

treewide: Remove uninitialized_var() usage

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused vari

treewide: Remove uninitialized_var() usage

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.

In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:

git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
xargs perl -pi -e \
's/\buninitialized_var\(([^\)]+)\)/\1/g;
s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'

drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.

No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
alpha, and m68k.

[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Reviewed-by: Leon Romanovsky <[email protected]> # drivers/infiniband and mlx4/mlx5
Acked-by: Jason Gunthorpe <[email protected]> # IB
Acked-by: Kalle Valo <[email protected]> # wireless drivers
Reviewed-by: Chao Yu <[email protected]> # erofs
Signed-off-by: Kees Cook <[email protected]>

show more ...

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of th

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation version 2 of the license

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 315 file(s).

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Allison Randal <[email protected]>
Reviewed-by: Armijn Hemel <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

show more ...

treewide: Switch printk users from %pf and %pF to %ps and %pS, respectively

%pF and %pf are functionally equivalent to %pS and %ps conversion
specifiers. The former are deprecated, therefore switch

treewide: Switch printk users from %pf and %pF to %ps and %pS, respectively

%pF and %pf are functionally equivalent to %pS and %ps conversion
specifiers. The former are deprecated, therefore switch the current users
to use the preferred variant.

The changes have been produced by the following command:

git grep -l '%p[fF]' | grep -v '^\(tools\|Documentation\)/' | \
while read i; do perl -i -pe 's/%pf/%ps/g; s/%pF/%pS/g;' $i; done

And verifying the result.

Link: http://lkml.kernel.org/r/[email protected]
Cc: Andy Shevchenko <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Sakari Ailus <[email protected]>
Acked-by: David Sterba <[email protected]> (for btrfs)
Acked-by: Mike Rapoport <[email protected]> (for mm/memblock.c)
Acked-by: Bjorn Helgaas <[email protected]> (for drivers/pci)
Acked-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>

show more ...

async: Add support for queueing on specific NUMA node

Introduce four new variants of the async_schedule_ functions that allow
scheduling on a specific NUMA node.

The first two functions are async_s

async: Add support for queueing on specific NUMA node

Introduce four new variants of the async_schedule_ functions that allow
scheduling on a specific NUMA node.

The first two functions are async_schedule_near and
async_schedule_near_domain end up mapping to async_schedule and
async_schedule_domain, but provide NUMA node specific functionality. They
replace the original functions which were moved to inline function
definitions that call the new functions while passing NUMA_NO_NODE.

The second two functions are async_schedule_dev and
async_schedule_dev_domain which provide NUMA specific functionality when
passing a device as the data member and that device has a NUMA node other
than NUMA_NO_NODE.

The main motivation behind this is to address the need to be able to
schedule device specific init work on specific NUMA nodes in order to
improve performance of memory initialization.

I have seen a significant improvement in initialziation time for persistent
memory as a result of this approach. In the case of 3TB of memory on a
single node the initialization time in the worst case went from 36s down to
about 26s for a 10s improvement. As such the data shows a general benefit
for affinitizing the async work to the node local to the device.

Reviewed-by: Bart Van Assche <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Signed-off-by: Alexander Duyck <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

show more ...

kernel/async.c: revert "async: simplify lowest_in_progress()"

This reverts commit 92266d6ef60c ("async: simplify lowest_in_progress()")
which was simply wrong: In the case where domain is NULL, we n

kernel/async.c: revert "async: simplify lowest_in_progress()"

This reverts commit 92266d6ef60c ("async: simplify lowest_in_progress()")
which was simply wrong: In the case where domain is NULL, we now use the
wrong offsetof() in the list_first_entry macro, so we don't actually
fetch the ->cookie value, but rather the eight bytes located
sizeof(struct list_head) further into the struct async_entry.

On 64 bit, that's the data member, while on 32 bit, that's a u64 built
from func and data in some order.

I think the bug happens to be harmless in practice: It obviously only
affects callers which pass a NULL domain, and AFAICT the only such
caller is

async_synchronize_full() ->
async_synchronize_full_domain(NULL) ->
async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, NULL)

and the ASYNC_COOKIE_MAX means that in practice we end up waiting for
the async_global_pending list to be empty - but it would break if
somebody happened to pass (void*)-1 as the data element to
async_schedule, and of course also if somebody ever does a
async_synchronize_cookie_domain(, NULL) with a "finite" cookie value.

Maybe the "harmless in practice" means this isn't -stable material. But
I'm not completely confident my quick git grep'ing is enough, and there
might be affected code in one of the earlier kernels that has since been
removed, so I'll leave the decision to the stable guys.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 92266d6ef60c "async: simplify lowest_in_progress()"
Signed-off-by: Rasmus Villemoes <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Adam Wallis <[email protected]>
Cc: Lai Jiangshan <[email protected]>
Cc: <[email protected]> [3.10+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

async: Adjust system_state checks

To enable smp_processor_id() and might_sleep() debug checks earlier, it's
required to add system states between SYSTEM_BOOTING and SYSTEM_RUNNING.

Adjust the syste

async: Adjust system_state checks

To enable smp_processor_id() and might_sleep() debug checks earlier, it's
required to add system states between SYSTEM_BOOTING and SYSTEM_RUNNING.

Adjust the system_state check in async_run_entry_fn() and
async_synchronize_cookie_domain() to handle the extra states.

Tested-by: Mark Rutland <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Arjan van de Ven <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

async: export current_is_async()

Introduced by 84b233adcca3 ("workqueue: implement current_is_async()").

Cc: Tejun Heo <[email protected]>
Signed-off-by: Lukas Wunner <[email protected]>
Acked-by: Tejun

async: export current_is_async()

Introduced by 84b233adcca3 ("workqueue: implement current_is_async()").

Cc: Tejun Heo <[email protected]>
Signed-off-by: Lukas Wunner <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>

show more ...

kernel/async.c: switch to pr_foo()

Signed-off-by: Ionut Alexa <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus To

kernel/async.c: switch to pr_foo()

Signed-off-by: Ionut Alexa <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

show more ...

async: rename and redefine async_func_ptr

A function type is typically defined as
typedef ret_type (*func)(args..)

but async_func_ptr is not. Redefine it.

Also rename async_func_ptr to async_func

async: rename and redefine async_func_ptr

A function type is typically defined as
typedef ret_type (*func)(args..)

but async_func_ptr is not. Redefine it.

Also rename async_func_ptr to async_func_t for _func_t suffix is more generic.

Signed-off-by: Lai Jiangshan <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>

show more ...

async: simplify lowest_in_progress()

The code in lowest_in_progress() are duplicated in two branches,
simplify them.

tj: Minor indentation adjustment.

Signed-off-by: Lai Jiangshan <[email protected]

async: simplify lowest_in_progress()

The code in lowest_in_progress() are duplicated in two branches,
simplify them.

tj: Minor indentation adjustment.

Signed-off-by: Lai Jiangshan <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>

show more ...

async: initialise list heads to fix crash

9fdb04cdc55 ("async: replace list of active domains with global list
of pending items") added a struct list_head global_list in struct
async_entry, which is

async: initialise list heads to fix crash

9fdb04cdc55 ("async: replace list of active domains with global list
of pending items") added a struct list_head global_list in struct
async_entry, which isn't initialised. This means that if
!domain->registered at __async_schedule(), then list_del_init() will
be called on the list head in async_run_entry_fn with both pointers
NULL, causing a crash. This is fixed by initialising both the
global_list and domain_list list_heads after kzalloc'ing the entry.

This was noticed due to dapm_power_widgets() which uses
ASYNC_DOMAIN_EXCLUSIVE, which initialises the domain->registered to 0.

Signed-off-by: James Hogan <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Reported-by: James Hogan <[email protected]>
Reported-by: Stephen Warren <[email protected]>

show more ...

async: replace list of active domains with global list of pending items

Global synchronization - async_synchronize_full() - is currently
implemented by keeping a list of all active registered domain

async: replace list of active domains with global list of pending items

Global synchronization - async_synchronize_full() - is currently
implemented by keeping a list of all active registered domains and
syncing them one by one until no domain is active.

While this isn't necessarily a complex scheme, it can easily be
simplified by keeping global list of the pending items of all
registered active domains instead of list of domains and simply using
the globl pending list the same way as domain syncing.

This patch replaces async_domains with async_global_pending and update
lowest_in_progress() to use the global pending list if @domain is
%NULL. async_synchronize_full_domain(NULL) is now allowed and
equivalent to async_synchronize_full(). As no one is calling with
NULL domain, this doesn't affect any existing users.

async_register_mutex is no longer necessary and dropped.

Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Linus Torvalds <[email protected]>

show more ...

async: keep pending tasks on async_domain and remove async_pending

Async kept single global pending list and per-domain running lists.
When an async item is queued, it's put on the global pending li

async: keep pending tasks on async_domain and remove async_pending

Async kept single global pending list and per-domain running lists.
When an async item is queued, it's put on the global pending list.
The item is moved to the per-domain running list when its execution
starts.

At this point, this design complicates execution and synchronization
without bringing any benefit. The list only matters for
synchronization which doesn't care whether a given async item is
pending or executing. Also, global synchronization is done by
iterating through all active registered async_domains, so the global
async_pending list doesn't help anything either.

Rename async_domain->running to async_domain->pending and put async
items directly there and remove when execution completes. This
simplifies lowest_in_progress() a lot - the first item on the pending
list is the one with the lowest cookie, and async_run_entry_fn()
doesn't have to mess with moving the item from pending to running.

After the change, whether a domain is empty or not can be trivially
determined by looking at async_domain->pending. Remove
async_domain->count and use list_empty() on pending instead.

Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Linus Torvalds <[email protected]>

show more ...

async: use ULLONG_MAX for infinity cookie value

Currently, next_cookie is used as the infinity value. In most cases,
this should work fine but it theoretically could bring subtle behavior
differenc

async: use ULLONG_MAX for infinity cookie value

Currently, next_cookie is used as the infinity value. In most cases,
this should work fine but it theoretically could bring subtle behavior
difference between async_synchronize_full() and
async_synchronize_full_domain().

async_synchronize_full() keeps waiting until there's no registered
async_entry left regardless of what next_cookie was when the function
was called. It guarantees that the queue is completely drained at
least once before returning.

However, async_synchronize_full_domain() doesn't. It synchronizes
upto next_cookie and if further async jobs are queued after the
next_cookie value to synchronize is decided, they won't be waited for.

For unrelated async jobs, the behavior difference doesn't matter;
however, if async jobs which are related (nested or otherwise) to the
executing ones are queued while sychronization is in progress, the
resulting behavior difference could be problematic.

This can be easily fixed by using ULLONG_MAX as the infinity value
instead. Define ASYNC_COOKIE_MAX as ULLONG_MAX and use it as the
infinity value for synchronization. This makes
async_synchronize_full_domain() fully drain the domain at least once
before returning, making its behavior match async_synchronize_full().

Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Linus Torvalds <[email protected]>

show more ...

async: bring sanity to the use of words domain and running

In the beginning, running lists were literal struct list_heads. Later
on, struct async_domain was added. For some reason, while the
conve

async: bring sanity to the use of words domain and running

In the beginning, running lists were literal struct list_heads. Later
on, struct async_domain was added. For some reason, while the
conversion substituted list_heads with async_domains, the variable
names weren't fully converted. In more places, "running" was used for
struct async_domain while other places adopted new "domain" name.

The situation is made much worse by having async_domain's running list
named "domain" and async_entry's field pointing to async_domain named
"running".

So, we end up with mix of "running" and "domain" for variable names
for async_domain, with the field names of async_domain and async_entry
swapped between "running" and "domain".

It feels almost intentionally made to be as confusing as possible.
Bring some sanity by

* Renaming all async_domain variables "domain".

* s/async_running/async_dfl_domain/

* s/async_domain->domain/async_domain->running/

* s/async_entry->running/async_entry->domain/

Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Linus Torvalds <[email protected]>

show more ...

async: fix __lowest_in_progress()

Commit 083b804c4d3e ("async: use workqueue for worker pool") made it
possible that async jobs are moved from pending to running out-of-order.
While pending async jo

async: fix __lowest_in_progress()

Commit 083b804c4d3e ("async: use workqueue for worker pool") made it
possible that async jobs are moved from pending to running out-of-order.
While pending async jobs will be queued and dispatched for execution in
the same order, nothing guarantees they'll enter "1) move self to the
running queue" of async_run_entry_fn() in the same order.

Before the conversion, async implemented its own worker pool. An async
worker, upon being woken up, fetches the first item from the pending
list, which kept the executing lists sorted. The conversion to
workqueue was done by adding work_struct to each async_entry and async
just schedules the work item. The queueing and dispatching of such work
items are still in order but now each worker thread is associated with a
specific async_entry and moves that specific async_entry to the
executing list. So, depending on which worker reaches that point
earlier, which is non-deterministic, we may end up moving an async_entry
with larger cookie before one with smaller one.

This broke __lowest_in_progress(). running->domain may not be properly
sorted and is not guaranteed to contain lower cookies than pending list
when not empty. Fix it by ensuring sort-inserting to the running list
and always looking at both pending and running when trying to determine
the lowest cookie.

Over time, the async synchronization implementation became quite messy.
We better restructure it such that each async_entry is linked to two
lists - one global and one per domain - and not move it when execution
starts. There's no reason to distinguish pending and running. They
behave the same for synchronization purposes.

Signed-off-by: Tejun Heo <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

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workqueue: implement current_is_async()

This function queries whether %current is an async worker executing an
async item. This will be used to implement warning on synchronous
request_module() fro

workqueue: implement current_is_async()

This function queries whether %current is an async worker executing an
async item. This will be used to implement warning on synchronous
request_module() from async workers.

Signed-off-by: Tejun Heo <[email protected]>

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