kernel timer API rework

In `config/kernel-timer.m4` refactor slightly to check more generally
for the new `timer_setup()` APIs, but also check the callback signature
because some kernels (notably 4.14) have the new `timer_setup()` API but
use the old callback signature. Also add a check for a `flags` member in
`struct timer_list`, which was added in 4.1-rc8.

Add compatibility shims to `include/spl/sys/timer.h` to allow using the
new timer APIs with the only two caveats being that the callback
argument type must be declared as `spl_timer_list_t` and an explicit
assignment is required to get the timer variable for the `timer_of()`
macro. So the callback would look like this:

```c
__cv_wakeup(spl_timer_list_t t)
{
        struct timer_list *tmr = (struct timer_list *)t;
	struct thing *parent = from_timer(parent, tmr,
		parent_timer_field);
	... /* do stuff with parent */
```

Make some minor changes to `spl-condvar.c` and `spl-taskq.c` to use the
new timer APIs instead of conditional code.

Reviewed-by: Tomohiro Kusumi <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rafael Kitover <[email protected]>
Closes #8647 

2 files changed, 25 insertions, 28 deletions

diff --git a/module/spl/spl-condvar.c b/module/spl/spl-condvar.c
index 1e6e38b78..a7a9d1db9 100644
--- a/module/spl/spl-condvar.c
+++ b/module/spl/spl-condvar.c
@@ -154,26 +154,39 @@ EXPORT_SYMBOL(__cv_wait_sig);
 #if defined(HAVE_IO_SCHEDULE_TIMEOUT)
 #define	spl_io_schedule_timeout(t)	io_schedule_timeout(t)
 #else
+
+struct spl_task_timer {
+	struct timer_list timer;
+	struct task_struct *task;
+};
+
 static void
-__cv_wakeup(unsigned long data)
+__cv_wakeup(spl_timer_list_t t)
 {
-	wake_up_process((struct task_struct *)data);
+	struct timer_list *tmr = (struct timer_list *)t;
+	struct spl_task_timer *task_timer = from_timer(task_timer, tmr, timer);
+
+	wake_up_process(task_timer->task);
 }
 
 static long
 spl_io_schedule_timeout(long time_left)
 {
 	long expire_time = jiffies + time_left;
-	struct timer_list timer;
+	struct spl_task_timer task_timer;
+	struct timer_list *timer = &task_timer.timer;
+
+	task_timer.task = current;
 
-	init_timer(&timer);
-	setup_timer(&timer, __cv_wakeup, (unsigned long)current);
-	timer.expires = expire_time;
-	add_timer(&timer);
+	timer_setup(timer, __cv_wakeup, 0);
+
+	timer->expires = expire_time;
+	add_timer(timer);
 
 	io_schedule();
 
-	del_timer_sync(&timer);
+	del_timer_sync(timer);
+
 	time_left = expire_time - jiffies;
 
 	return (time_left < 0 ? 0 : time_left);
diff --git a/module/spl/spl-taskq.c b/module/spl/spl-taskq.c
index 7684257be..a39f94e4c 100644
--- a/module/spl/spl-taskq.c
+++ b/module/spl/spl-taskq.c
@@ -24,6 +24,7 @@
  *  Solaris Porting Layer (SPL) Task Queue Implementation.
  */
 
+#include <sys/timer.h>
 #include <sys/taskq.h>
 #include <sys/kmem.h>
 #include <sys/tsd.h>
@@ -242,20 +243,13 @@ task_expire_impl(taskq_ent_t *t)
 	wake_up(&tq->tq_work_waitq);
 }
 
-#ifdef HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST
 static void
-task_expire(struct timer_list *tl)
+task_expire(spl_timer_list_t tl)
 {
-	taskq_ent_t *t = from_timer(t, tl, tqent_timer);
+	struct timer_list *tmr = (struct timer_list *)tl;
+	taskq_ent_t *t = from_timer(t, tmr, tqent_timer);
 	task_expire_impl(t);
 }
-#else
-static void
-task_expire(unsigned long data)
-{
-	task_expire_impl((taskq_ent_t *)data);
-}
-#endif
 
 /*
  * Returns the lowest incomplete taskqid_t.  The taskqid_t may
@@ -597,9 +591,6 @@ taskq_dispatch(taskq_t *tq, task_func_t func, void *arg, uint_t flags)
 	t->tqent_func = func;
 	t->tqent_arg = arg;
 	t->tqent_taskq = tq;
-#ifndef HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST
-	t->tqent_timer.data = 0;
-#endif
 	t->tqent_timer.function = NULL;
 	t->tqent_timer.expires = 0;
 	t->tqent_birth = jiffies;
@@ -649,9 +640,6 @@ taskq_dispatch_delay(taskq_t *tq, task_func_t func, void *arg,
 	t->tqent_func = func;
 	t->tqent_arg = arg;
 	t->tqent_taskq = tq;
-#ifndef HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST
-	t->tqent_timer.data = (unsigned long)t;
-#endif
 	t->tqent_timer.function = task_expire;
 	t->tqent_timer.expires = (unsigned long)expire_time;
 	add_timer(&t->tqent_timer);
@@ -744,11 +732,7 @@ taskq_init_ent(taskq_ent_t *t)
 {
 	spin_lock_init(&t->tqent_lock);
 	init_waitqueue_head(&t->tqent_waitq);
-#ifdef HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST
 	timer_setup(&t->tqent_timer, NULL, 0);
-#else
-	init_timer(&t->tqent_timer);
-#endif
 	INIT_LIST_HEAD(&t->tqent_list);
 	t->tqent_id = 0;
 	t->tqent_func = NULL;