Revert "Remove misguided HAVE_MUTEX_OWNER check"

This reverts commit d89616f which
introduced some build failures which need to be resolved before
this can be merged.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs#633

config/spl-build.m4

@@ -49,6 +49,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_USLEEP_RANGE
 	SPL_AC_KMEM_CACHE_ALLOCFLAGS
 	SPL_AC_WAIT_ON_BIT
+	SPL_AC_MUTEX_OWNER
 	SPL_AC_INODE_LOCK
 	SPL_AC_GROUP_INFO_GID
 	SPL_AC_KMEM_CACHE_CREATE_USERCOPY
@@ -1561,6 +1562,35 @@ AC_DEFUN([SPL_AC_WAIT_ON_BIT], [
 	])
 ])
 
+dnl #
+dnl # Check whether mutex has owner with task_struct type.
+dnl #
+dnl # Note that before Linux 3.0, mutex owner is of type thread_info.
+dnl #
+dnl # Note that in Linux 3.18, the condition for owner is changed from
+dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP) to
+dnl # defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_MUTEX_SPIN_ON_OWNER)
+dnl #
+AC_DEFUN([SPL_AC_MUTEX_OWNER], [
+	AC_MSG_CHECKING([whether mutex has owner])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Werror"
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/mutex.h>
+		#include <linux/spinlock.h>
+	],[
+		DEFINE_MUTEX(m);
+		struct task_struct *t __attribute__ ((unused));
+		t = m.owner;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_MUTEX_OWNER, 1, [yes])
+	],[
+		AC_MSG_RESULT(no)
+	])
+	EXTRA_KCFLAGS="$tmp_flags"
+])
+
 dnl #
 dnl # 4.7 API change
 dnl # i_mutex is changed to i_rwsem. Instead of directly using

include/sys/mutex.h

@@ -40,8 +40,10 @@ typedef enum {
 typedef struct {
 	struct mutex		m_mutex;
 	spinlock_t		m_lock;	/* used for serializing mutex_exit */
+#ifndef HAVE_MUTEX_OWNER
 	/* only when kernel doesn't have owner */
 	kthread_t		*m_owner;
+#endif
 #ifdef CONFIG_LOCKDEP
 	kmutex_type_t		m_type;
 #endif /* CONFIG_LOCKDEP */
@@ -56,16 +58,24 @@ spl_mutex_set_owner(kmutex_t *mp)
 	 * kernel will handle its owner, so we don't need to do anything if it
 	 * is defined.
 	 */
+#ifndef HAVE_MUTEX_OWNER
 	mp->m_owner = current;
+#endif
 }
 
 static inline void
 spl_mutex_clear_owner(kmutex_t *mp)
 {
+#ifndef HAVE_MUTEX_OWNER
 	mp->m_owner = NULL;
+#endif
 }
 
+#ifdef HAVE_MUTEX_OWNER
 #define	mutex_owner(mp)		(ACCESS_ONCE(MUTEX(mp)->owner))
+#else
+#define	mutex_owner(mp)		(ACCESS_ONCE((mp)->m_owner))
+#endif
 #define	mutex_owned(mp)		(mutex_owner(mp) == current)
 #define	MUTEX_HELD(mp)		mutex_owned(mp)
 #define	MUTEX_NOT_HELD(mp)	(!MUTEX_HELD(mp))