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[SCSI] async: make async_synchronize_full() flush all work regardless…

… of domain

In response to an async related regression James noted:

  "My theory is that this is an init problem: The assumption in a lot of
   our code is that async_synchronize_full() waits for everything ... even
   the domain specific async schedules, which isn't true."

...so make this assumption true.

Each domain, including the default one, registers itself on a global domain
list when work is scheduled.  Once all entries complete it exits that
list.  Waiting for the list to be empty syncs all in-flight work across
all domains.

Domains can opt-out of global syncing if they are declared as exclusive
ASYNC_DOMAIN_EXCLUSIVE().  All stack-based domains have been declared
exclusive since the domain may go out of scope as soon as the last work
item completes.

Statically declared domains are mostly ok, but async_unregister_domain()
is there to close any theoretical races with pending
async_synchronize_full waiters at module removal time.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Reported-by: Meelis Roos <mroos@linux.ee>
Reported-by: Eldad Zack <eldadzack@gmail.com>
Tested-by: Eldad Zack <eldad@fogrefinery.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
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1 parent 2955b47 commit a4683487f90bfe3049686fc5c566bdc1ad03ace6 @djbw djbw committed with James Bottomley Jul 10, 2012
Showing with 43 additions and 2 deletions.
  1. +1 −0 drivers/scsi/scsi.c
  2. +1 −0 include/linux/async.h
  3. +41 −2 kernel/async.c
View
@@ -1355,6 +1355,7 @@ static void __exit exit_scsi(void)
scsi_exit_devinfo();
scsi_exit_procfs();
scsi_exit_queue();
+ async_unregister_domain(&scsi_sd_probe_domain);
}
subsys_initcall(init_scsi);
View
@@ -46,6 +46,7 @@ struct async_domain {
extern async_cookie_t async_schedule(async_func_ptr *ptr, void *data);
extern async_cookie_t async_schedule_domain(async_func_ptr *ptr, void *data,
struct async_domain *domain);
+void async_unregister_domain(struct async_domain *domain);
extern void async_synchronize_full(void);
extern void async_synchronize_full_domain(struct async_domain *domain);
extern void async_synchronize_cookie(async_cookie_t cookie);
View
@@ -63,7 +63,9 @@ static async_cookie_t next_cookie = 1;
static LIST_HEAD(async_pending);
static ASYNC_DOMAIN(async_running);
+static LIST_HEAD(async_domains);
static DEFINE_SPINLOCK(async_lock);
+static DEFINE_MUTEX(async_register_mutex);
struct async_entry {
struct list_head list;
@@ -145,6 +147,8 @@ static void async_run_entry_fn(struct work_struct *work)
/* 3) remove self from the running queue */
spin_lock_irqsave(&async_lock, flags);
list_del(&entry->list);
+ if (running->registered && --running->count == 0)
+ list_del_init(&running->node);
/* 4) free the entry */
kfree(entry);
@@ -187,6 +191,8 @@ static async_cookie_t __async_schedule(async_func_ptr *ptr, void *data, struct a
spin_lock_irqsave(&async_lock, flags);
newcookie = entry->cookie = next_cookie++;
list_add_tail(&entry->list, &async_pending);
+ if (running->registered && running->count++ == 0)
+ list_add_tail(&running->node, &async_domains);
atomic_inc(&entry_count);
spin_unlock_irqrestore(&async_lock, flags);
@@ -236,12 +242,42 @@ EXPORT_SYMBOL_GPL(async_schedule_domain);
*/
void async_synchronize_full(void)
{
+ mutex_lock(&async_register_mutex);
do {
- async_synchronize_cookie(next_cookie);
- } while (!list_empty(&async_running.domain) || !list_empty(&async_pending));
+ struct async_domain *domain = NULL;
+
+ spin_lock_irq(&async_lock);
+ if (!list_empty(&async_domains))
+ domain = list_first_entry(&async_domains, typeof(*domain), node);
+ spin_unlock_irq(&async_lock);
+
+ async_synchronize_cookie_domain(next_cookie, domain);
+ } while (!list_empty(&async_domains));
+ mutex_unlock(&async_register_mutex);
}
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)
+{
+ mutex_lock(&async_register_mutex);
+ spin_lock_irq(&async_lock);
+ WARN_ON(!domain->registered || !list_empty(&domain->node) ||
+ !list_empty(&domain->domain));
+ domain->registered = 0;
+ spin_unlock_irq(&async_lock);
+ mutex_unlock(&async_register_mutex);
+}
+EXPORT_SYMBOL_GPL(async_unregister_domain);
+
/**
* async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
* @domain: running list to synchronize on
@@ -268,6 +304,9 @@ void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain
{
ktime_t uninitialized_var(starttime), delta, endtime;
+ if (!running)
+ return;
+
if (initcall_debug && system_state == SYSTEM_BOOTING) {
printk(KERN_DEBUG "async_waiting @ %i\n", task_pid_nr(current));
starttime = ktime_get();

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