linux/kernel/async.c

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/*
* async.c: Asynchronous function calls for boot performance
*
* (C) Copyright 2009 Intel Corporation
* Author: Arjan van de Ven <arjan@linux.intel.com>
*
* 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.
*/
/*
Goals and Theory of Operation
The primary goal of this feature is to reduce the kernel boot time,
by doing various independent hardware delays and discovery operations
decoupled and not strictly serialized.
More specifically, the asynchronous function call concept allows
certain operations (primarily during system boot) to happen
asynchronously, out of order, while these operations still
have their externally visible parts happen sequentially and in-order.
(not unlike how out-of-order CPUs retire their instructions in order)
Key to the asynchronous function call implementation is the concept of
a "sequence cookie" (which, although it has an abstracted type, can be
thought of as a monotonically incrementing number).
The async core will assign each scheduled event such a sequence cookie and
pass this to the called functions.
The asynchronously called function should before doing a globally visible
operation, such as registering device numbers, call the
async_synchronize_cookie() function and pass in its own cookie. The
async_synchronize_cookie() function will make sure that all asynchronous
operations that were scheduled prior to the operation corresponding with the
cookie have completed.
Subsystem/driver initialization code that scheduled asynchronous probe
functions, but which shares global resources with other drivers/subsystems
that do not use the asynchronous call feature, need to do a full
synchronization with the async_synchronize_full() function, before returning
from their init function. This is to maintain strict ordering between the
asynchronous and synchronous parts of the kernel.
*/
#include <linux/async.h>
#include <linux/atomic.h>
#include <linux/ktime.h>
#include <linux/export.h>
#include <linux/wait.h>
#include <linux/sched.h>
include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h percpu.h is included by sched.h and module.h and thus ends up being included when building most .c files. percpu.h includes slab.h which in turn includes gfp.h making everything defined by the two files universally available and complicating inclusion dependencies. percpu.h -> slab.h dependency is about to be removed. Prepare for this change by updating users of gfp and slab facilities include those headers directly instead of assuming availability. As this conversion needs to touch large number of source files, the following script is used as the basis of conversion. http://userweb.kernel.org/~tj/misc/slabh-sweep.py The script does the followings. * Scan files for gfp and slab usages and update includes such that only the necessary includes are there. ie. if only gfp is used, gfp.h, if slab is used, slab.h. * When the script inserts a new include, it looks at the include blocks and try to put the new include such that its order conforms to its surrounding. It's put in the include block which contains core kernel includes, in the same order that the rest are ordered - alphabetical, Christmas tree, rev-Xmas-tree or at the end if there doesn't seem to be any matching order. * If the script can't find a place to put a new include (mostly because the file doesn't have fitting include block), it prints out an error message indicating which .h file needs to be added to the file. The conversion was done in the following steps. 1. The initial automatic conversion of all .c files updated slightly over 4000 files, deleting around 700 includes and adding ~480 gfp.h and ~3000 slab.h inclusions. The script emitted errors for ~400 files. 2. Each error was manually checked. Some didn't need the inclusion, some needed manual addition while adding it to implementation .h or embedding .c file was more appropriate for others. This step added inclusions to around 150 files. 3. The script was run again and the output was compared to the edits from #2 to make sure no file was left behind. 4. Several build tests were done and a couple of problems were fixed. e.g. lib/decompress_*.c used malloc/free() wrappers around slab APIs requiring slab.h to be added manually. 5. The script was run on all .h files but without automatically editing them as sprinkling gfp.h and slab.h inclusions around .h files could easily lead to inclusion dependency hell. Most gfp.h inclusion directives were ignored as stuff from gfp.h was usually wildly available and often used in preprocessor macros. Each slab.h inclusion directive was examined and added manually as necessary. 6. percpu.h was updated not to include slab.h. 7. Build test were done on the following configurations and failures were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my distributed build env didn't work with gcov compiles) and a few more options had to be turned off depending on archs to make things build (like ipr on powerpc/64 which failed due to missing writeq). * x86 and x86_64 UP and SMP allmodconfig and a custom test config. * powerpc and powerpc64 SMP allmodconfig * sparc and sparc64 SMP allmodconfig * ia64 SMP allmodconfig * s390 SMP allmodconfig * alpha SMP allmodconfig * um on x86_64 SMP allmodconfig 8. percpu.h modifications were reverted so that it could be applied as a separate patch and serve as bisection point. Given the fact that I had only a couple of failures from tests on step 6, I'm fairly confident about the coverage of this conversion patch. If there is a breakage, it's likely to be something in one of the arch headers which should be easily discoverable easily on most builds of the specific arch. Signed-off-by: Tejun Heo <tj@kernel.org> Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
2010-03-24 08:04:11 +00:00
#include <linux/slab.h>
#include <linux/workqueue.h>
#include "workqueue_internal.h"
static async_cookie_t next_cookie = 1;
#define MAX_WORK 32768
#define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
static LIST_HEAD(async_global_pending); /* pending from all registered doms */
static ASYNC_DOMAIN(async_dfl_domain);
static DEFINE_SPINLOCK(async_lock);
struct async_entry {
struct list_head domain_list;
struct list_head global_list;
struct work_struct work;
async_cookie_t cookie;
async_func_t func;
void *data;
struct async_domain *domain;
};
static DECLARE_WAIT_QUEUE_HEAD(async_done);
static atomic_t entry_count;
static async_cookie_t lowest_in_progress(struct async_domain *domain)
{
struct list_head *pending;
async_cookie_t ret = ASYNC_COOKIE_MAX;
unsigned long flags;
spin_lock_irqsave(&async_lock, flags);
if (domain)
pending = &domain->pending;
else
pending = &async_global_pending;
if (!list_empty(pending))
ret = list_first_entry(pending, struct async_entry,
domain_list)->cookie;
spin_unlock_irqrestore(&async_lock, flags);
return ret;
}
/*
* pick the first pending entry and run it
*/
static void async_run_entry_fn(struct work_struct *work)
{
struct async_entry *entry =
container_of(work, struct async_entry, work);
unsigned long flags;
ktime_t uninitialized_var(calltime), delta, rettime;
/* 1) run (and print duration) */
if (initcall_debug && system_state == SYSTEM_BOOTING) {
pr_debug("calling %lli_%pF @ %i\n",
(long long)entry->cookie,
entry->func, task_pid_nr(current));
calltime = ktime_get();
}
entry->func(entry->data, entry->cookie);
if (initcall_debug && system_state == SYSTEM_BOOTING) {
rettime = ktime_get();
delta = ktime_sub(rettime, calltime);
pr_debug("initcall %lli_%pF returned 0 after %lld usecs\n",
(long long)entry->cookie,
entry->func,
(long long)ktime_to_ns(delta) >> 10);
}
/* 2) remove self from the pending queues */
spin_lock_irqsave(&async_lock, flags);
list_del_init(&entry->domain_list);
list_del_init(&entry->global_list);
/* 3) free the entry */
kfree(entry);
atomic_dec(&entry_count);
spin_unlock_irqrestore(&async_lock, flags);
/* 4) wake up any waiters */
wake_up(&async_done);
}
static async_cookie_t __async_schedule(async_func_t func, void *data, struct async_domain *domain)
{
struct async_entry *entry;
unsigned long flags;
async_cookie_t newcookie;
/* allow irq-off callers */
entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
/*
* If we're out of memory or if there's too much work
* pending already, we execute synchronously.
*/
if (!entry || atomic_read(&entry_count) > MAX_WORK) {
kfree(entry);
spin_lock_irqsave(&async_lock, flags);
newcookie = next_cookie++;
spin_unlock_irqrestore(&async_lock, flags);
/* low on memory.. run synchronously */
func(data, newcookie);
return newcookie;
}
INIT_LIST_HEAD(&entry->domain_list);
INIT_LIST_HEAD(&entry->global_list);
INIT_WORK(&entry->work, async_run_entry_fn);
entry->func = func;
entry->data = data;
entry->domain = domain;
spin_lock_irqsave(&async_lock, flags);
/* allocate cookie and queue */
newcookie = entry->cookie = next_cookie++;
list_add_tail(&entry->domain_list, &domain->pending);
if (domain->registered)
list_add_tail(&entry->global_list, &async_global_pending);
atomic_inc(&entry_count);
spin_unlock_irqrestore(&async_lock, flags);
module, async: async_synchronize_full() on module init iff async is used If the default iosched is built as module, the kernel may deadlock while trying to load the iosched module on device probe if the probing was running off async. This is because async_synchronize_full() at the end of module init ends up waiting for the async job which initiated the module loading. async A modprobe 1. finds a device 2. registers the block device 3. request_module(default iosched) 4. modprobe in userland 5. load and init module 6. async_synchronize_full() Async A waits for modprobe to finish in request_module() and modprobe waits for async A to finish in async_synchronize_full(). Because there's no easy to track dependency once control goes out to userland, implementing properly nested flushing is difficult. For now, make module init perform async_synchronize_full() iff module init has queued async jobs as suggested by Linus. This avoids the described deadlock because iosched module doesn't use async and thus wouldn't invoke async_synchronize_full(). This is hacky and incomplete. It will deadlock if async module loading nests; however, this works around the known problem case and seems to be the best of bad options. For more details, please refer to the following thread. http://thread.gmane.org/gmane.linux.kernel/1420814 Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Alex Riesen <raa.lkml@gmail.com> Tested-by: Ming Lei <ming.lei@canonical.com> Tested-by: Alex Riesen <raa.lkml@gmail.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-01-16 02:52:51 +00:00
/* mark that this task has queued an async job, used by module init */
current->flags |= PF_USED_ASYNC;
/* schedule for execution */
queue_work(system_unbound_wq, &entry->work);
return newcookie;
}
/**
* async_schedule - schedule a function for asynchronous execution
* @func: function to execute asynchronously
* @data: data pointer to pass to the function
*
* Returns an async_cookie_t that may be used for checkpointing later.
* Note: This function may be called from atomic or non-atomic contexts.
*/
async_cookie_t async_schedule(async_func_t func, void *data)
{
return __async_schedule(func, data, &async_dfl_domain);
}
EXPORT_SYMBOL_GPL(async_schedule);
/**
* async_schedule_domain - schedule a function for asynchronous execution within a certain domain
* @func: function to execute asynchronously
* @data: data pointer to pass to the function
* @domain: the domain
*
* Returns an async_cookie_t that may be used for checkpointing later.
* @domain may be used in the async_synchronize_*_domain() functions to
* wait within a certain synchronization domain rather than globally. A
* synchronization domain is specified via @domain. Note: This function
* may be called from atomic or non-atomic contexts.
*/
async_cookie_t async_schedule_domain(async_func_t func, void *data,
struct async_domain *domain)
{
return __async_schedule(func, data, domain);
}
EXPORT_SYMBOL_GPL(async_schedule_domain);
/**
* async_synchronize_full - synchronize all asynchronous function calls
*
* This function waits until all asynchronous function calls have been done.
*/
void async_synchronize_full(void)
{
async_synchronize_full_domain(NULL);
}
EXPORT_SYMBOL_GPL(async_synchronize_full);
/**
* async_unregister_domain - ensure no more anonymous waiters on this domain
* @domain: idle domain to flush out of any async_synchronize_full instances
*
* async_synchronize_{cookie|full}_domain() are not flushed since callers
* of these routines should know the lifetime of @domain
*
* Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
*/
void async_unregister_domain(struct async_domain *domain)
{
spin_lock_irq(&async_lock);
WARN_ON(!domain->registered || !list_empty(&domain->pending));
domain->registered = 0;
spin_unlock_irq(&async_lock);
}
EXPORT_SYMBOL_GPL(async_unregister_domain);
/**
* async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
* @domain: the domain to synchronize
*
* This function waits until all asynchronous function calls for the
* synchronization domain specified by @domain have been done.
*/
void async_synchronize_full_domain(struct async_domain *domain)
{
async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
}
EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
/**
* async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
* @cookie: async_cookie_t to use as checkpoint
* @domain: the domain to synchronize (%NULL for all registered domains)
*
* This function waits until all asynchronous function calls for the
* synchronization domain specified by @domain submitted prior to @cookie
* have been done.
*/
void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
{
ktime_t uninitialized_var(starttime), delta, endtime;
if (initcall_debug && system_state == SYSTEM_BOOTING) {
pr_debug("async_waiting @ %i\n", task_pid_nr(current));
starttime = ktime_get();
}
wait_event(async_done, lowest_in_progress(domain) >= cookie);
if (initcall_debug && system_state == SYSTEM_BOOTING) {
endtime = ktime_get();
delta = ktime_sub(endtime, starttime);
pr_debug("async_continuing @ %i after %lli usec\n",
task_pid_nr(current),
(long long)ktime_to_ns(delta) >> 10);
}
}
EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
/**
* async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
* @cookie: async_cookie_t to use as checkpoint
*
* This function waits until all asynchronous function calls prior to @cookie
* have been done.
*/
void async_synchronize_cookie(async_cookie_t cookie)
{
async_synchronize_cookie_domain(cookie, &async_dfl_domain);
}
EXPORT_SYMBOL_GPL(async_synchronize_cookie);
/**
* current_is_async - is %current an async worker task?
*
* Returns %true if %current is an async worker task.
*/
bool current_is_async(void)
{
struct worker *worker = current_wq_worker();
return worker && worker->current_func == async_run_entry_fn;
}
EXPORT_SYMBOL_GPL(current_is_async);