svn commit: r355789 - head/sys/kern

[Mateusz Guzik]

Author: mjg
Date: Mon Dec 16 00:04:33 2019
New Revision: 355789
URL: https://svnweb.freebsd.org/changeset/base/355789

Log:
  mtx: eliminate recursion support from thread lock
  
  Now that it is not used after schedlock changes got merged.
  
  Note the unlock routine temporarily still checks for it on account of just using
  regular spin unlock.
  
  This is a prelude towards a general clean up.

Modified:
  head/sys/kern/kern_mutex.c

Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c	Sun Dec 15 23:28:53 2019	(r355788)
+++ head/sys/kern/kern_mutex.c	Mon Dec 16 00:04:33 2019	(r355789)
@@ -797,10 +797,9 @@ thread_lock_validate(struct mtx *m, int opts, const ch
 	KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
 	    ("thread_lock() of sleep mutex %s @ %s:%d",
 	    m->lock_object.lo_name, file, line));
-	if (mtx_owned(m))
-		KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
-		    ("thread_lock: recursed on non-recursive mutex %s @ %s:%d\n",
-		    m->lock_object.lo_name, file, line));
+	KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) == 0,
+	    ("thread_lock: got a recursive mutex %s @ %s:%d\n",
+	    m->lock_object.lo_name, file, line));
 	WITNESS_CHECKORDER(&m->lock_object,
 	    opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
 }
@@ -818,7 +817,7 @@ _thread_lock(struct thread *td)
 #endif
 {
 	struct mtx *m;
-	uintptr_t tid, v;
+	uintptr_t tid;
 
 	tid = (uintptr_t)curthread;
 
@@ -827,19 +826,14 @@ _thread_lock(struct thread *td)
 	spinlock_enter();
 	m = td->td_lock;
 	thread_lock_validate(m, 0, file, line);
-	v = MTX_READ_VALUE(m);
-	if (__predict_true(v == MTX_UNOWNED)) {
-		if (__predict_false(!_mtx_obtain_lock(m, tid)))
-			goto slowpath_unlocked;
-	} else if (v == tid) {
-		m->mtx_recurse++;
-	} else
+	if (__predict_false(m == &blocked_lock))
 		goto slowpath_unlocked;
+	if (__predict_false(!_mtx_obtain_lock(m, tid)))
+		goto slowpath_unlocked;
 	if (__predict_true(m == td->td_lock)) {
 		WITNESS_LOCK(&m->lock_object, LOP_EXCLUSIVE, file, line);
 		return;
 	}
-	MPASS(m->mtx_recurse == 0);
 	_mtx_release_lock_quick(m);
 slowpath_unlocked:
 	spinlock_exit();
@@ -907,11 +901,7 @@ retry:
 					break;
 				continue;
 			}
-			if (v == tid) {
-				m->mtx_recurse++;
-				MPASS(m == td->td_lock);
-				break;
-			}
+			MPASS(v != tid);
 			lock_profile_obtain_lock_failed(&m->lock_object,
 			    &contested, &waittime);
 			/* Give interrupts a chance while we spin. */
@@ -932,7 +922,6 @@ retry:
 		}
 		if (m == td->td_lock)
 			break;
-		MPASS(m->mtx_recurse == 0);
 		_mtx_release_lock_quick(m);
 	}
 	LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
@@ -946,9 +935,8 @@ retry:
 #ifdef KDTRACE_HOOKS
 	spin_time += lockstat_nsecs(&m->lock_object);
 #endif
-	if (m->mtx_recurse == 0)
-		LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(spin__acquire, m,
-		    contested, waittime, file, line);
+	LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(spin__acquire, m, contested,
+	    waittime, file, line);
 #ifdef KDTRACE_HOOKS
 	if (lda.spin_cnt != 0)
 		LOCKSTAT_RECORD1(thread__spin, m, spin_time);