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[bug][kernel][ipc][mutex]只有在PRIO策略下进行优先级继承 #4771

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[bug][kernel][ipc][mutex]只有在PRIO策略下进行优先级继承 #4771

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[kernel][ipc][mutex]只有在PRIO策略下进行优先级继承
mysterywolf Jun 7, 2021
3aa35bf
Merge branch 'master' into mutexinvert
mysterywolf Jun 7, 2021
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6 changes: 4 additions & 2 deletions src/ipc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,7 @@
* 2020-10-11 Meco Man add value overflow-check code
* 2021-01-03 Meco Man implement rt_mb_urgent()
* 2021-05-30 Meco Man implement rt_mutex_trytake()
* 2021-06-07 Meco Man only RT_IPC_FLAG_PRIO needs to execute priority inheritance
*/

#include <rtthread.h>
Expand Down Expand Up @@ -755,8 +756,9 @@ rt_err_t rt_mutex_take(rt_mutex_t mutex, rt_int32_t time)
RT_DEBUG_LOG(RT_DEBUG_IPC, ("mutex_take: suspend thread: %s\n",
thread->name));

/* change the owner thread priority of mutex */
if (thread->current_priority < mutex->owner->current_priority)
/* priority inheritance */
if (thread->current_priority < mutex->owner->current_priority
&& mutex->parent.parent.flag == RT_IPC_FLAG_PRIO)
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如果改了这个，如果软件包或者客户代码里用fifo的方式做了互斥，也就退化成了信号量了，没有了防止优先级反转的特效，下次release版本需要强调这个API的改动了。

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@Guozhanxin Guozhanxin Jun 13, 2021 •
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优先级反转，之前指的好像不是获取同一个资源排队的问题，指的是一个线程1在获取的资源A之后再去获取资源B，其中A是以互斥量的形式获取的。因此如果此时有更高优先级的线程2来获取A，那么此时就要提高线程1的优先级，保证它不会被低优先级的打断，可以及时释放资源A。

所以我又有了疑惑，因为我们之前的文档说明“mutex具有防止优先级反转的作用”，指的应该就是这个优先级继承的机制，和其内部的排队机制应该是无关的。但是，FIFO的排队机制本身就会导致优先级被反转……

而且revert掉之前的一个pr之后，FIFO下的优先级继承本来就是假的了，没有起到防止优先级反转的作用。所以以后，mutex只有以Pro的形式创建才具有防止优先级反转的功能。。。所以FIFO在mutex里存在的意义是什么？

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刚才我计算了一下，在FIFO处理所谓“优先级反转”的问题，根本无法防止优先级反转，因为防止优先级反转的先决条件就是等待列表按照PRIO排序才可以。

{
/* change the owner thread priority */
rt_thread_control(mutex->owner,
Expand Down