Changes in kernel/generic/src/synch/mutex.c [9f2f5ee:597fa24] in mainline

File:

• kernel/generic/src/synch/mutex.c (modified) (8 diffs)

kernel/generic/src/synch/mutex.c

@@ -1 +1 @@
 /*
  * Copyright (c) 2001-2004 Jakub Jermar
- * Copyright (c) 2025 Jiří Zárevúcky
+ * Copyright (c) 2023 Jiří Zárevúcky
  * All rights reserved.
  *
@@ -39 +39 @@
 #include <assert.h>
 #include <errno.h>
-#include <proc/thread.h>
-#include <stdatomic.h>
 #include <synch/mutex.h>
 #include <synch/semaphore.h>
+#include <arch.h>
+#include <stacktrace.h>
+#include <cpu.h>
+#include <proc/thread.h>
 
 /** Initialize mutex.
@@ -54 +56 @@
 }
 
-/** A race in mtx->owner access is unavoidable, so we have to make
- * access to it formally atomic. These are convenience functions to
- * read/write the variable without memory barriers, since we don't need
- * them and C11 atomics default to the strongest possible memory ordering
- * by default, which is utterly ridiculous.
- */
-static inline thread_t *_get_owner(mutex_t *mtx)
-{
-        return atomic_load_explicit(&mtx->owner, memory_order_relaxed);
-}
-
-/** Counterpart to _get_owner(). */
-static inline void _set_owner(mutex_t *mtx, thread_t *owner)
-{
-        atomic_store_explicit(&mtx->owner, owner, memory_order_relaxed);
-}
-
 /** Find out whether the mutex is currently locked.
  *
@@ -79 +64 @@
 bool mutex_locked(mutex_t *mtx)
 {
-        if (!THREAD)
-                return mtx->nesting > 0;
+        errno_t rc = semaphore_trydown(&mtx->sem);
+        if (rc == EOK) {
+                semaphore_up(&mtx->sem);
+        }
+        return rc != EOK;
+}
 
-        return _get_owner(mtx) == THREAD;
+static void mutex_lock_active(mutex_t *mtx)
+{
+        assert((mtx->type == MUTEX_ACTIVE) || !THREAD);
+
+        const unsigned deadlock_treshold = 100000000;
+        unsigned int cnt = 0;
+        bool deadlock_reported = false;
+
+        while (semaphore_trydown(&mtx->sem) != EOK) {
+                if (cnt++ > deadlock_treshold) {
+                        printf("cpu%u: looping on active mutex %p\n", CPU->id, mtx);
+                        stack_trace();
+                        cnt = 0;
+                        deadlock_reported = true;
+                }
+        }
+
+        if (deadlock_reported)
+                printf("cpu%u: not deadlocked\n", CPU->id);
 }
 
@@ -91 +98 @@
 void mutex_lock(mutex_t *mtx)
 {
-        if (!THREAD) {
-                assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
+        if (mtx->type == MUTEX_RECURSIVE && mtx->owner == THREAD) {
+                assert(THREAD);
                 mtx->nesting++;
                 return;
         }
 
-        if (_get_owner(mtx) == THREAD) {
-                /* This will also detect nested locks on a non-recursive mutex. */
-                assert(mtx->type == MUTEX_RECURSIVE);
-                assert(mtx->nesting > 0);
-                mtx->nesting++;
+        if (mtx->type == MUTEX_ACTIVE || !THREAD) {
+                mutex_lock_active(mtx);
                 return;
         }
 
         semaphore_down(&mtx->sem);
-
-        _set_owner(mtx, THREAD);
-        assert(mtx->nesting == 0);
+        mtx->owner = THREAD;
         mtx->nesting = 1;
 }
@@ -121 +123 @@
 errno_t mutex_lock_timeout(mutex_t *mtx, uint32_t usec)
 {
-        if (!THREAD) {
-                assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
-                mtx->nesting++;
-                return EOK;
+        if (usec != 0) {
+                assert(mtx->type != MUTEX_ACTIVE);
+                assert(THREAD);
         }
 
-        if (_get_owner(mtx) == THREAD) {
-                assert(mtx->type == MUTEX_RECURSIVE);
-                assert(mtx->nesting > 0);
+        if (mtx->type == MUTEX_RECURSIVE && mtx->owner == THREAD) {
+                assert(THREAD);
                 mtx->nesting++;
                 return EOK;
@@ -135 +135 @@
 
         errno_t rc = semaphore_down_timeout(&mtx->sem, usec);
-        if (rc != EOK)
-                return rc;
-
-        _set_owner(mtx, THREAD);
-        assert(mtx->nesting == 0);
-        mtx->nesting = 1;
-        return EOK;
+        if (rc == EOK) {
+                mtx->owner = THREAD;
+                mtx->nesting = 1;
+        }
+        return rc;
 }
 
@@ -159 +157 @@
 void mutex_unlock(mutex_t *mtx)
 {
-        if (--mtx->nesting > 0) {
-                assert(mtx->type == MUTEX_RECURSIVE);
-                return;
+        if (mtx->type == MUTEX_RECURSIVE) {
+                assert(mtx->owner == THREAD);
+                if (--mtx->nesting > 0)
+                        return;
+                mtx->owner = NULL;
         }
-
-        assert(mtx->nesting == 0);
-
-        if (!THREAD)
-                return;
-
-        assert(_get_owner(mtx) == THREAD);
-        _set_owner(mtx, NULL);
-
         semaphore_up(&mtx->sem);
 }