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 <kusumi.tomohiro@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rafael Kitover <rkitover@gmail.com>
Closes openzfs#8647

config/kernel-timer.m4

@@ -1,32 +1,73 @@
+dnl # 4.14-rc3 API change
+dnl # https://lwn.net/Articles/735887/
 dnl #
-dnl # 4.15 API change
-dnl # https://lkml.org/lkml/2017/11/25/90
 dnl # Check if timer_list.func get passed a timer_list or an unsigned long
 dnl # (older kernels).  Also sanity check the from_timer() and timer_setup()
 dnl # macros are available as well, since they will be used in the same newer
 dnl # kernels that support the new timer_list.func signature.
 dnl #
-AC_DEFUN([ZFS_AC_KERNEL_TIMER_FUNCTION_TIMER_LIST], [
-	AC_MSG_CHECKING([whether timer_list.function gets a timer_list])
+dnl # Also check for the existance of flags in struct timer_list, they were
+dnl # added in 4.1-rc8 via 0eeda71bc30d.
+
+AC_DEFUN([ZFS_AC_KERNEL_TIMER_SETUP], [
+	AC_MSG_CHECKING([whether timer_setup() is available])
 	tmp_flags="$EXTRA_KCFLAGS"
 	EXTRA_KCFLAGS="-Werror"
+
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/timer.h>
-		void task_expire(struct timer_list *tl) {}
+
+		struct my_task_timer {
+			struct timer_list timer;
+			int data;
+		};
+
+		void task_expire(struct timer_list *tl)
+		{
+			struct my_task_timer *task_timer = from_timer(task_timer, tl, timer);
+			task_timer->data = 42;
+		}
+	],[
+		struct my_task_timer task_timer;
+		timer_setup(&task_timer.timer, task_expire, 0);
 	],[
-		#ifndef from_timer
-		#error "No from_timer() macro"
-		#endif
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_KERNEL_TIMER_SETUP, 1,
+		    [timer_setup() is available])
+	],[
+		AC_MSG_RESULT(no)
+	])
 
-		struct timer_list timer;
-		timer.function = task_expire;
-		timer_setup(&timer, NULL, 0);
+	AC_MSG_CHECKING([whether timer function expects timer_list])
+
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/timer.h>
+		void task_expire(struct timer_list *tl) {}
+	],[
+		struct timer_list tl;
+		tl.function = task_expire;
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST, 1,
 		    [timer_list.function gets a timer_list])
 	],[
 		AC_MSG_RESULT(no)
 	])
+
+	AC_MSG_CHECKING([whether struct timer_list has flags])
+
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/timer.h>
+	],[
+		struct timer_list tl;
+		tl.flags = 2;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_KERNEL_TIMER_LIST_FLAGS, 1,
+		    [struct timer_list has a flags member])
+	],[
+		AC_MSG_RESULT(no)
+	])
+
 	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel.m4

@@ -38,7 +38,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_GROUP_INFO_GID
 	ZFS_AC_KERNEL_WRITE
 	ZFS_AC_KERNEL_READ
-	ZFS_AC_KERNEL_TIMER_FUNCTION_TIMER_LIST
+	ZFS_AC_KERNEL_TIMER_SETUP
 	ZFS_AC_KERNEL_DECLARE_EVENT_CLASS
 	ZFS_AC_KERNEL_CURRENT_BIO_TAIL
 	ZFS_AC_KERNEL_SUPER_USER_NS

include/os/linux/spl/sys/timer.h

@@ -72,4 +72,29 @@ usleep_range(unsigned long min, unsigned long max)
 #define	USEC_TO_TICK(us)		usecs_to_jiffies(us)
 #define	NSEC_TO_TICK(ns)		usecs_to_jiffies(ns / NSEC_PER_USEC)
 
+#ifndef from_timer
+#define	from_timer(var, timer, timer_field) \
+	container_of(timer, typeof(*var), timer_field)
+#endif
+
+#ifdef HAVE_KERNEL_TIMER_FUNCTION_TIMER_LIST
+typedef struct timer_list *spl_timer_list_t;
+#else
+typedef unsigned long spl_timer_list_t;
+#endif
+
+#ifndef HAVE_KERNEL_TIMER_SETUP
+
+static inline void
+timer_setup(struct timer_list *timer, void (*func)(spl_timer_list_t), u32 fl)
+{
+#ifdef HAVE_KERNEL_TIMER_LIST_FLAGS
+	(timer)->flags = fl;
+#endif
+	init_timer(timer);
+	setup_timer(timer, func, (spl_timer_list_t)(timer));
+}
+
+#endif /* HAVE_KERNEL_TIMER_SETUP */
+
 #endif  /* _SPL_TIMER_H */

module/os/linux/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);

module/os/linux/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;