Use kernel provided mutex owner

To reduce mutex footprint, we detect the existence of owner in kernel mutex, and rely on it if it exists. Note that before Linux 3.0, mutex owner is of type thread_info. Also note that, in Linux 3.18, the condition for owner is changed from CONFIG_DEBUG_MUTEXES || CONFIG_SMP to CONFIG_DEBUG_MUTEXES || CONFIG_MUTEX_SPIN_ON_OWNER Signed-off-by: Chunwei Chen <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes openzfs#540
behlendorf · Apr 26, 2016 · cdd39dd · cdd39dd
1 parent 224817e
commit cdd39dd
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diff --git a/config/spl-build.m4 b/config/spl-build.m4
@@ -44,6 +44,7 @@ AC_DEFUN([SPL_AC_CONFIG_KERNEL], [
 	SPL_AC_USLEEP_RANGE
 	SPL_AC_KMEM_CACHE_ALLOCFLAGS
 	SPL_AC_WAIT_ON_BIT
+	SPL_AC_MUTEX_OWNER
 ])
 
 AC_DEFUN([SPL_AC_MODULE_SYMVERS], [
@@ -1447,3 +1448,31 @@ AC_DEFUN([SPL_AC_WAIT_ON_BIT], [
 		AC_MSG_RESULT(no)
 	])
 ])
+
+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="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Werror"
+	SPL_LINUX_TRY_COMPILE([
+		#include <linux/mutex.h>
+	],[
+		DEFINE_MUTEX(m);
+		struct task_struct *t __attribute__ ((unused));
+		t = m.owner;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_MUTEX_OWNER, 1, [yes])
+	],[
+		AC_MSG_RESULT(no)
+	])
+	EXTRA_KCFLAGS="$tmp_flags"
+])
diff --git a/include/sys/mutex.h b/include/sys/mutex.h
@@ -40,7 +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 */
@@ -51,16 +54,28 @@ typedef struct {
 static inline void
 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))