From 6df4c1b667e29397f235fb1dba79bad4c1d26389 Mon Sep 17 00:00:00 2001
From: acevest <zhaoyanbai@126.com>
Date: Tue, 30 Apr 2024 22:33:41 +0800
Subject: [PATCH] =?utf8?q?=E7=94=A8semaphore=5Fwaiter=5Ft=E5=AE=9E?=
 =?utf8?q?=E7=8E=B0down=E5=92=8Cup?=
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---
 include/sched.h    |   4 +-
 include/task.h     |  12 ++---
 include/wait.h     |   3 +-
 kernel/clock.c     |   4 +-
 kernel/exit.c      |   2 +-
 kernel/fork.c      |   6 +--
 kernel/sched.c     |  42 +++++++--------
 kernel/semaphore.c | 130 +++++++++------------------------------------
 8 files changed, 62 insertions(+), 141 deletions(-)

diff --git a/include/sched.h b/include/sched.h
index 7bc55cc..1c6da97 100644
--- a/include/sched.h
+++ b/include/sched.h
@@ -25,9 +25,9 @@
 
 void schedule();
 
-extern task_union root_task;
+extern task_t root_task;
 
-extern void load_cr3(task_union *tsk);
+extern void load_cr3(task_t *tsk);
 
 extern list_head_t all_tasks;
 extern list_head_t delay_tasks;
diff --git a/include/task.h b/include/task.h
index 795b28e..d47538e 100644
--- a/include/task.h
+++ b/include/task.h
@@ -72,7 +72,7 @@ typedef union task_union {
 
         list_head_t pend;  // 某些条件串成一个链表
 
-        list_head_t wait;
+        // list_head_t wait;
 
         uint32_t sched_cnt;       // 被调度换上CPU的次数
         uint32_t sched_keep_cnt;  // 时间片到了，但是没有被换出，又重新执行的次数
@@ -83,12 +83,12 @@ typedef union task_union {
     };
 
     unsigned char stack[TASK_SIZE];
-} task_union;
+} task_t;
 
-task_union *alloc_task_union();
+task_t *alloc_task_t();
 
-static inline task_union *get_current() {
-    task_union *tsk;
+static inline task_t *get_current() {
+    task_t *tsk;
     asm("andl %%esp, %0;" : "=r"(tsk) : "0"(~(TASK_SIZE - 1)));
     return tsk;
 }
@@ -97,7 +97,7 @@ static inline task_union *get_current() {
 
 static inline pid_t sysc_getpid() { return current->pid; }
 
-task_union *find_task(pid_t pid);
+task_t *find_task(pid_t pid);
 
 #define ROOT_TSK_PID (0)
 
diff --git a/include/wait.h b/include/wait.h
index b591ea3..a3fd1c3 100644
--- a/include/wait.h
+++ b/include/wait.h
@@ -15,14 +15,13 @@
 #include <irq.h>
 #include <list.h>
 #include <sched.h>
-union task_union;
 
 typedef struct wait_queue_head {
     list_head_t task_list;
 } wait_queue_head_t;
 
 typedef struct {
-    union task_union *task;
+    task_t *task;
     list_head_t task_list;
 } wait_queue_t;
 
diff --git a/kernel/clock.c b/kernel/clock.c
index b104efe..0bcd146 100644
--- a/kernel/clock.c
+++ b/kernel/clock.c
@@ -53,11 +53,11 @@ void clk_handler(unsigned int irq, pt_regs_t *regs, void *dev_id) {
 // 后续放到一个内核任务中去做，需要先把禁止内核抢占做了
 const char *task_state(unsigned int state);
 void clk_bh_handler(void *arg) {
-    task_union *p = 0;
+    task_t *p = 0;
     list_head_t *t = 0;
     list_head_t *pos = 0;
     list_for_each_safe(pos, t, &delay_tasks) {
-        p = list_entry(pos, task_union, pend);
+        p = list_entry(pos, task_t, pend);
         // printk("%s state: %s\n", p->name, task_state(p->state));
         assert(p->state == TASK_WAIT);
         assert(p->delay_jiffies != 0);
diff --git a/kernel/exit.c b/kernel/exit.c
index 44c136f..d57dc41 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -19,7 +19,7 @@ int sysc_exit(int status) {
     irq_save(flags);
     current->state = TASK_EXITING;
 
-    task_union *t = current;
+    task_t *t = current;
 
     irq_restore(flags);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 27b7037..ab6d887 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -19,15 +19,15 @@ extern pid_t get_next_pid();
 extern list_head_t all_tasks;
 
 int do_fork(pt_regs_t *regs, unsigned long flags) {
-    task_union *tsk;
-    tsk = alloc_task_union();
+    task_t *tsk;
+    tsk = alloc_task_t();
 
     printd("fork task %08x flags %08x\n", tsk, flags);
     if (tsk == NULL) {
         panic("can not malloc PCB");
     }
 
-    memcpy(tsk, current, sizeof(task_union));
+    memcpy(tsk, current, sizeof(task_t));
 
     assert(tsk->magic == TASK_MAGIC);
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 2f832ab..b2af86e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -23,7 +23,7 @@
 #include "mm.h"
 #include "msr.h"
 
-task_union root_task __attribute__((__aligned__(PAGE_SIZE)));
+task_t root_task __attribute__((__aligned__(PAGE_SIZE)));
 
 // 暂时不考虑pid回绕问题
 pid_t get_next_pid() {
@@ -40,7 +40,7 @@ pid_t get_next_pid() {
     return pid;
 }
 
-void load_cr3(task_union *tsk) { LoadCR3(tsk->cr3); }
+void load_cr3(task_t *tsk) { LoadCR3(tsk->cr3); }
 
 extern pde_t __initdata init_pgd[PDECNT_PER_PAGE] __attribute__((__aligned__(PAGE_SIZE)));
 
@@ -86,7 +86,7 @@ void init_root_task() {
     printk("init_root_task tss.esp0 %08x\n", tss.esp0);
 }
 
-kmem_cache_t *task_union_cache;
+kmem_cache_t *task_t_cache;
 
 void setup_tasks() {
     INIT_LIST_HEAD(&all_tasks);
@@ -94,15 +94,15 @@ void setup_tasks() {
 
     init_root_task();
 
-    task_union_cache = kmem_cache_create("task_union", sizeof(task_union), PAGE_SIZE);
-    if (0 == task_union_cache) {
+    task_t_cache = kmem_cache_create("task_t", sizeof(task_t), PAGE_SIZE);
+    if (0 == task_t_cache) {
         panic("setup tasks failed. out of memory");
     }
 }
 
-task_union *alloc_task_union() {
-    task_union *task;
-    task = (task_union *)kmem_cache_alloc(task_union_cache, 0);
+task_t *alloc_task_t() {
+    task_t *task;
+    task = (task_t *)kmem_cache_alloc(task_t_cache, 0);
     return task;
 }
 
@@ -116,7 +116,7 @@ void switch_to() {
 #endif
 }
 
-void context_switch(task_union *prev, task_union *next) {
+void context_switch(task_t *prev, task_t *next) {
     unsigned long eax, ebx, ecx, edx, esi, edi;
     asm volatile(
         "pushfl;"
@@ -135,14 +135,14 @@ void context_switch(task_union *prev, task_union *next) {
         : "memory");
 }
 
-task_union *find_task(pid_t pid) {
-    task_union *p = 0;
+task_t *find_task(pid_t pid) {
+    task_t *p = 0;
     list_head_t *pos = 0, *tmp = 0;
 
     unsigned long iflags;
     irq_save(iflags);
     list_for_each_safe(pos, tmp, &all_tasks) {
-        p = list_entry(pos, task_union, list);
+        p = list_entry(pos, task_t, list);
         if (p->pid == pid) {
             break;
         }
@@ -165,11 +165,11 @@ const char *task_state(unsigned int state) {
 }
 
 void debug_print_all_tasks() {
-    task_union *p = 0;
+    task_t *p = 0;
     list_head_t *pos = 0, *t = 0;
     printl(MPL_TASK_TITLE, "         NAME       STATE TK/PI REASON     SCHED      KEEP");
     list_for_each_safe(pos, t, &all_tasks) {
-        p = list_entry(pos, task_union, list);
+        p = list_entry(pos, task_t, list);
         printl(MPL_TASK_0 + p->pid, "%08x%s%-6s:%u %s %02u/%02u %-10s %-10u %-10u", p,
                p->state == TASK_RUNNING ? ">" : " ", p->name, p->pid, task_state(p->state), p->ticks, p->priority,
                p->reason, p->sched_cnt, p->sched_keep_cnt);
@@ -177,9 +177,9 @@ void debug_print_all_tasks() {
 }
 
 void schedule() {
-    task_union *root = &root_task;
-    task_union *sel = 0;
-    task_union *p = 0;
+    task_t *root = &root_task;
+    task_t *sel = 0;
+    task_t *p = 0;
     list_head_t *pos = 0, *t = 0;
 
     assert(current->ticks <= TASK_MAX_PRIORITY);
@@ -198,7 +198,7 @@ void schedule() {
     }
 
     list_for_each_safe(pos, t, &all_tasks) {
-        p = list_entry(pos, task_union, list);
+        p = list_entry(pos, task_t, list);
 
         if (p == &root_task) {
             continue;
@@ -230,8 +230,8 @@ void schedule() {
         }
     }
 
-    task_union *prev = current;
-    task_union *next = sel != 0 ? sel : root;
+    task_t *prev = current;
+    task_t *next = sel != 0 ? sel : root;
 
     next->state = TASK_RUNNING;
     next->reason = "";
@@ -252,6 +252,6 @@ void schedule() {
 }
 
 void debug_sched() {
-    task_union *p = list_entry(current->list.next, task_union, list);
+    task_t *p = list_entry(current->list.next, task_t, list);
     p->state = (p->state == TASK_READY) ? TASK_WAIT : TASK_READY;
 }
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index c7ff128..6000451 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -10,40 +10,46 @@
 #include <sched.h>
 #include <semaphore.h>
 
+typedef struct semaphore_waiter {
+    list_head_t list;
+    task_t *task;
+
+    // 在Linux内核中这个结构体有一个up字段，这个字段的作用是防止进程被错误地唤醒
+    // 例如
+    // 如果一个进程在等待信号量时收到了一个信号（signal），它可能会被内核唤醒以处理这个信号。
+    // 但是，如果这个进程没有真正获得信号量（即up字段为false）它应该继续等待信号量而不是继续执行
+    // 本内核暂时还用不到这个字段
+
+} semaphore_waiter_t;
+
 void semaphore_init(semaphore_t *s, unsigned int v) {
     s->cnt = v;
     INIT_LIST_HEAD(&(s->wait_list));
 }
 
-#if 1
 volatile void down(semaphore_t *s) {
     unsigned long iflags;
     irq_save(iflags);
 
     if (likely(s->cnt > 0)) {
         s->cnt--;
+        irq_restore(iflags);
     } else {
-        task_union *task = current;
-        list_add_tail(&task->wait, &s->wait_list);
+        task_t *task = current;
+        semaphore_waiter_t waiter;
+        waiter.task = task;
+        INIT_LIST_HEAD(&waiter.list);
+        list_add(&waiter.list, &s->wait_list);
+
+        irq_restore(iflags);
 
         task->state = TASK_WAIT;
         task->reason = "down";
 
         schedule();
     }
-
-    irq_restore(iflags);
 }
 
-// volatile bool try_down(semaphore_t *s) {
-//     unsigned long iflags;
-//     irq_save(iflags);
-
-//     // if(s->cnt )
-
-//     irq_restore(iflags);
-// }
-
 volatile void up(semaphore_t *s) {
     unsigned long iflags;
     irq_save(iflags);
@@ -51,105 +57,21 @@ volatile void up(semaphore_t *s) {
     if (list_empty(&s->wait_list)) {
         s->cnt++;
     } else {
-        task_union *task = list_first_entry(&s->wait_list, task_union, wait);
-        list_del(&task->wait);
+        semaphore_waiter_t *waiter = list_first_entry(&s->wait_list, semaphore_waiter_t, list);
+        list_del(&waiter->list);
+        task_t *task = waiter->task;
+
         task->state = TASK_READY;
         task->reason = "up";
 
-        // 按理这里应该调用schedule再重新调度一次
-        // 原因是有可能多个任务都在一个循环里争抢一个锁
-        // 如果这里不让当前任务尝试放弃CPU重新调度，则在下一轮循环中它又可能抢到锁
-        // 这种情况如果一直发生，就可能导致其它任务一直抢不到
-        //
-        // 但这里为什么又没调用schedule呢？
-        // 这是因为在目前在ide_irq_bh_handler里调用了up来唤醒磁盘任务
+        // 这里不应该调用schedule()再重新调度一次
+        // 例如，目前在ide_irq_bh_handler里调用了up来唤醒磁盘任务
         // 而ide_irq_bh_handler又是中断的底半处理，不应该切换任务
         // 否则会引起irq里的reenter问题，导致不能再进底半处理，也无法切换任务
-        // 这里暂时先保持这样，后续再来解决这里
-        // schedule();
-    }
-
-    irq_restore(iflags);
-}
-
-#else
-
-typedef struct semaphore_waiter {
-    list_head_t list;
-    task_union *task;
-    int up;
-} semaphore_waiter_t;
-
-#define SEMAPHORE_WAITER_INITIALIZER(name, task) \
-    { .list = LIST_HEAD_INIT((name).list), .task = task, .up = 0 }
-
-#define DECLARE_SEMAPHORE_WAITER(name, task) semaphore_waiter_t name = SEMAPHORE_WAITER_INITIALIZER(name, task)
-
-volatile void __down(semaphore_t *s) {
-    task_union *task = current;
-    DECLARE_SEMAPHORE_WAITER(waiter, task);
-    list_add_tail(&waiter.list, &s->wait_list);
-
-    while (true) {
-        task->state = TASK_WAIT;
-        task->reason = "down";
-        schedule();
-
-        assert(waiter.up == 1);
-        if (waiter.up) {
-            break;
-        }
-    }
-}
-
-volatile void down(semaphore_t *s) {
-    unsigned long iflags;
-    irq_save(iflags);
-
-    if (likely(s->cnt > 0)) {
-        s->cnt--;
-    } else {
-        __down(s);
-    }
-
-    irq_restore(iflags);
-}
-
-volatile void __up(semaphore_t *s) {
-    semaphore_waiter_t *waiter = list_first_entry(&s->wait_list, semaphore_waiter_t, list);
-    list_del(&waiter->list);
-    waiter->up = 1;
-
-    waiter->task->state = TASK_READY;
-    waiter->task->reason = "up";
-
-    // 按理这里应该调用schedule再重新调度一次
-    // 原因是有可能多个任务都在一个循环里争抢一个锁
-    // 如果这里不让当前任务尝试放弃CPU重新调度，则在下一轮循环中它又可能抢到锁
-    // 这种情况如果一直发生，就可能导致其它任务一直抢不到
-    //
-    // 但这里为什么又没调用schedule呢？
-    // 这是因为在目前在ide_irq_bh_handler里调用了up来唤醒磁盘任务
-    // 而ide_irq_bh_handler又是中断的底半处理，不应该切换任务
-    // 否则会引起irq里的reenter问题，导致不能再进底半处理，也无法切换任务
-    // 这里暂时先保持这样，后续再来解决这里
-    // schedule();
-}
-
-volatile void up(semaphore_t *s) {
-    unsigned long iflags;
-    irq_save(iflags);
-
-    // if (likely(list_empty(&s->wait_list))) {
-    if (list_empty(&s->wait_list)) {
-        s->cnt++;
-    } else {
-        __up(s);
     }
 
     irq_restore(iflags);
 }
-#endif
 
 void mutex_lock(semaphore_t *s) { down(s); }
 void mutex_unlock(semaphore_t *s) { up(s); }
-- 
2.44.0