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SLOW_WORK: Wait for outstanding work items belonging to a module to clear

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Wait for outstanding slow work items belonging to a module to clear when
unregistering that module as a user of the facility.  This prevents the put_ref
code of a work item from being taken away before it returns.

Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells
2009-11-19 18:10:23 +00:00
parent 66b00a7c93
commit 3d7a641e54
8 changed files with 150 additions and 16 deletions
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132
kernel/slow-work.c
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@ -22,6 +22,8 @@
#define SLOW_WORK_OOM_TIMEOUT (5 * HZ) /* can't start new threads for 5s after
* OOM */
#define SLOW_WORK_THREAD_LIMIT 255 /* abs maximum number of slow-work threads */
static void slow_work_cull_timeout(unsigned long);
static void slow_work_oom_timeout(unsigned long);
@ -46,7 +48,7 @@ static unsigned vslow_work_proportion = 50; /* % of threads that may process
#ifdef CONFIG_SYSCTL
static const int slow_work_min_min_threads = 2;
static int slow_work_max_max_threads = 255;
static int slow_work_max_max_threads = SLOW_WORK_THREAD_LIMIT;
static const int slow_work_min_vslow = 1;
static const int slow_work_max_vslow = 99;
@ -97,6 +99,23 @@ static DEFINE_TIMER(slow_work_cull_timer, slow_work_cull_timeout, 0, 0);
static DEFINE_TIMER(slow_work_oom_timer, slow_work_oom_timeout, 0, 0);
static struct slow_work slow_work_new_thread; /* new thread starter */
/*
* slow work ID allocation (use slow_work_queue_lock)
*/
static DECLARE_BITMAP(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
/*
* Unregistration tracking to prevent put_ref() from disappearing during module
* unload
*/
#ifdef CONFIG_MODULES
static struct module *slow_work_thread_processing[SLOW_WORK_THREAD_LIMIT];
static struct module *slow_work_unreg_module;
static struct slow_work *slow_work_unreg_work_item;
static DECLARE_WAIT_QUEUE_HEAD(slow_work_unreg_wq);
static DEFINE_MUTEX(slow_work_unreg_sync_lock);
#endif
/*
* The queues of work items and the lock governing access to them. These are
* shared between all the CPUs. It doesn't make sense to have per-CPU queues
@ -149,8 +168,11 @@ static unsigned slow_work_calc_vsmax(void)
* Attempt to execute stuff queued on a slow thread. Return true if we managed
* it, false if there was nothing to do.
*/
static bool slow_work_execute(void)
static bool slow_work_execute(int id)
{
#ifdef CONFIG_MODULES
struct module *module;
#endif
struct slow_work *work = NULL;
unsigned vsmax;
bool very_slow;
@ -186,6 +208,12 @@ static bool slow_work_execute(void)
} else {
very_slow = false; /* avoid the compiler warning */
}
#ifdef CONFIG_MODULES
if (work)
slow_work_thread_processing[id] = work->owner;
#endif
spin_unlock_irq(&slow_work_queue_lock);
if (!work)
@ -219,7 +247,18 @@ static bool slow_work_execute(void)
spin_unlock_irq(&slow_work_queue_lock);
}
/* sort out the race between module unloading and put_ref() */
work->ops->put_ref(work);
#ifdef CONFIG_MODULES
module = slow_work_thread_processing[id];
slow_work_thread_processing[id] = NULL;
smp_mb();
if (slow_work_unreg_work_item == work ||
slow_work_unreg_module == module)
wake_up_all(&slow_work_unreg_wq);
#endif
return true;
auto_requeue:
@ -232,6 +271,7 @@ auto_requeue:
else
list_add_tail(&work->link, &slow_work_queue);
spin_unlock_irq(&slow_work_queue_lock);
slow_work_thread_processing[id] = NULL;
return true;
}
@ -368,13 +408,22 @@ static inline bool slow_work_available(int vsmax)
*/
static int slow_work_thread(void *_data)
{
int vsmax;
int vsmax, id;
DEFINE_WAIT(wait);
set_freezable();
set_user_nice(current, -5);
/* allocate ourselves an ID */
spin_lock_irq(&slow_work_queue_lock);
id = find_first_zero_bit(slow_work_ids, SLOW_WORK_THREAD_LIMIT);
BUG_ON(id < 0 || id >= SLOW_WORK_THREAD_LIMIT);
__set_bit(id, slow_work_ids);
spin_unlock_irq(&slow_work_queue_lock);
sprintf(current->comm, "kslowd%03u", id);
for (;;) {
vsmax = vslow_work_proportion;
vsmax *= atomic_read(&slow_work_thread_count);
@ -395,7 +444,7 @@ static int slow_work_thread(void *_data)
vsmax *= atomic_read(&slow_work_thread_count);
vsmax /= 100;
if (slow_work_available(vsmax) && slow_work_execute()) {
if (slow_work_available(vsmax) && slow_work_execute(id)) {
cond_resched();
if (list_empty(&slow_work_queue) &&
list_empty(&vslow_work_queue) &&
@ -412,6 +461,10 @@ static int slow_work_thread(void *_data)
break;
}
spin_lock_irq(&slow_work_queue_lock);
__clear_bit(id, slow_work_ids);
spin_unlock_irq(&slow_work_queue_lock);
if (atomic_dec_and_test(&slow_work_thread_count))
complete_and_exit(&slow_work_last_thread_exited, 0);
return 0;
@ -475,6 +528,7 @@ static void slow_work_new_thread_execute(struct slow_work *work)
}
static const struct slow_work_ops slow_work_new_thread_ops = {
.owner = THIS_MODULE,
.get_ref = slow_work_new_thread_get_ref,
.put_ref = slow_work_new_thread_put_ref,
.execute = slow_work_new_thread_execute,
@ -546,12 +600,13 @@ static int slow_work_max_threads_sysctl(struct ctl_table *table, int write,
/**
* slow_work_register_user - Register a user of the facility
* @module: The module about to make use of the facility
*
* Register a user of the facility, starting up the initial threads if there
* aren't any other users at this point. This will return 0 if successful, or
* an error if not.
*/
int slow_work_register_user(void)
int slow_work_register_user(struct module *module)
{
struct task_struct *p;
int loop;
@ -598,14 +653,79 @@ error:
}
EXPORT_SYMBOL(slow_work_register_user);
/*
* wait for all outstanding items from the calling module to complete
* - note that more items may be queued whilst we're waiting
*/
static void slow_work_wait_for_items(struct module *module)
{
DECLARE_WAITQUEUE(myself, current);
struct slow_work *work;
int loop;
mutex_lock(&slow_work_unreg_sync_lock);
add_wait_queue(&slow_work_unreg_wq, &myself);
for (;;) {
spin_lock_irq(&slow_work_queue_lock);
/* first of all, we wait for the last queued item in each list
* to be processed */
list_for_each_entry_reverse(work, &vslow_work_queue, link) {
if (work->owner == module) {
set_current_state(TASK_UNINTERRUPTIBLE);
slow_work_unreg_work_item = work;
goto do_wait;
}
}
list_for_each_entry_reverse(work, &slow_work_queue, link) {
if (work->owner == module) {
set_current_state(TASK_UNINTERRUPTIBLE);
slow_work_unreg_work_item = work;
goto do_wait;
}
}
/* then we wait for the items being processed to finish */
slow_work_unreg_module = module;
smp_mb();
for (loop = 0; loop < SLOW_WORK_THREAD_LIMIT; loop++) {
if (slow_work_thread_processing[loop] == module)
goto do_wait;
}
spin_unlock_irq(&slow_work_queue_lock);
break; /* okay, we're done */
do_wait:
spin_unlock_irq(&slow_work_queue_lock);
schedule();
slow_work_unreg_work_item = NULL;
slow_work_unreg_module = NULL;
}
remove_wait_queue(&slow_work_unreg_wq, &myself);
mutex_unlock(&slow_work_unreg_sync_lock);
}
/**
* slow_work_unregister_user - Unregister a user of the facility
* @module: The module whose items should be cleared
*
* Unregister a user of the facility, killing all the threads if this was the
* last one.
*
* This waits for all the work items belonging to the nominated module to go
* away before proceeding.
*/
void slow_work_unregister_user(void)
void slow_work_unregister_user(struct module *module)
{
/* first of all, wait for all outstanding items from the calling module
* to complete */
if (module)
slow_work_wait_for_items(module);
/* then we can actually go about shutting down the facility if need
* be */
mutex_lock(&slow_work_user_lock);
BUG_ON(slow_work_user_count <= 0);