Home System Tutorial LINUX :Linux process freezing technology: Make your system more stable

:Linux process freezing technology: Make your system more stable

Feb 10, 2024 am 10:18 AM
linux linux tutorial linux system linux command shell script system recovery embeddedlinux Getting started with linux linux learning

Have you ever encountered various problems that occur when the system is hibernating? For example, the file system is damaged, hibernation image creation fails, device suspend is abnormal, etc. These problems can be solved through Linux process freezing technology.

  1. Process freezing technology (freezing of tasks) refers to placing user processes and some kernel threads in a "controllable" pause state when the system hibernates or suspends.
  2. Without freezing technology, the process can be suspended at any schedulable point, and will not be suspended and migrated until cpu_down. This can cause a lot of problems for the system:
    1. It is possible to corrupt the file system. Between the time the system creates the hibernate image and the time the CPU goes down, if there are processes that are still modifying the contents of the file system, this will result in the file system being unable to be fully restored after the system is restored;
    2. It may cause the creation of hibernation image to fail. Creating a hibernation image requires sufficient memory space, but if there are still processes applying for memory during this period, the creation may fail;
    3. It is possible to interfere with the device's suspend and resume. Before the CPU is down, during device suspend, if the process is still accessing the device, especially when accessing competing resources, it may cause a device suspend exception;
    4. It may cause the process to sense system hibernation. The ideal state of system hibernation is that all tasks are unaware of the hibernation process and automatically resume work after waking up. However, some processes, such as a certain process, require all CPUs to be online to work properly. If the process does not freeze, it will Work abnormally.
  3. Frozen objects are entities in the kernel that can be scheduled for execution, including user processes, kernel threads, and work_queue. User processes can be frozen by default, which is implemented by borrowing the signal processing mechanism; kernel threads and work_queue cannot be frozen by default. A few kernel threads and work_queue specify the freezeable flag when they are created. These tasks need to judge the freeze status. When the system When entering freezing, the operation is automatically suspended. Kernel threads can determine the freezing status by calling kthread_freezable_should_stop, and actively call __refrigerator to enter freezing; work_queue determines the max_active attribute. If max_active=0, new work cannot be queued, and all work is delayed.
:Linux process freezing technology: Make your system more stable

There are three important global variables that mark the system freeze status: pm_freezing, system_freezing_cnt and pm_nosig_freezing. If they are all 0, it means that the system has not entered freezing; system_freezing_cnt>0 means that the system has entered freezing, and pm_freezing=true means Freeze the user process. pm_nosig_freezing=true means freezing the kernel thread and workqueue. They will be set in freeze_processes and freeze_kernel_threads, and cleared in thaw_processes and thaw_kernel_threads.
The fake_signal_wake_up function cleverly makes use of the signal processing mechanism. It only sets the TIF_SIGPENDING bit of the task, but does not pass any signal, and then wakes up the task; in this way, the task will enter the signal processing process when returning to user mode, check the freeze status of the system, and handle it accordingly. .
The code for the task to actively call try_to_freeze is as follows:

```

```

1. static inline bool try_to_freeze_unsafe(void)
2. {
3. if (likely(!freezing(current))) //检查系统是否处于freezing状态
4. return false;
5. return __refrigerator(false); //主动进入冻结
6. }
7.  
8. static inline bool freezing(struct task_struct *p)
9. {
10. if (likely(!atomic_read(&system_freezing_cnt))) //系统总体进入freezing
11. return false;
12. return freezing_slow_path(p);
13. }
14.  
15. bool freezing_slow_path(struct task_struct *p)
16. {
17. if (p->flags & PF_NOFREEZE) //当前进程是否允许冻结
18. return false;
19.  
20. if (pm_nosig_freezing || cgroup_freezing(p)) //系统冻结kernel threads
21. return true;
22.  
23. if (pm_freezing && !(p->flags & PF_KTHREAD)) //系统冻结用户进程
24. return true;
25.  
26. return false;
27. }
Copy after login

The main function to enter the frozen state until recovery: bool __refrigerator(bool check_kthr_stop)

1. {
2. ...
3. for (;;) {
4. set_current_state(TASK_UNINTERRUPTIBLE); //设置进程为UNINTERRUPTIBLE状态
5.  
6. spin_lock_irq(&freezer_lock);
7. current->flags |= PF_FROZEN; //设置已冻结状态
8. if (!freezing(current) ||
9. (check_kthr_stop && kthread_should_stop())) //判断系统是否还处于冻结
10. current->flags &= ~PF_FROZEN; //如果系统已解冻,则取消冻结状态
11. spin_unlock_irq(&freezer_lock);
12.  
13. if (!(current->flags & PF_FROZEN)) //如果已取消冻结,跳出循环,恢复执行
14. break;
15. was_frozen = true;
16. schedule();
17. }
18. ......
19. }
Copy after login

In short, Linux process freezing technology is a very useful technology that can help you avoid some potential problems and make your system more stable. If you want to learn more about this technology, check out the resources provided in this article.

The above is the detailed content of :Linux process freezing technology: Make your system more stable. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

What computer configuration is required for vscode What computer configuration is required for vscode Apr 15, 2025 pm 09:48 PM

VS Code system requirements: Operating system: Windows 10 and above, macOS 10.12 and above, Linux distribution processor: minimum 1.6 GHz, recommended 2.0 GHz and above memory: minimum 512 MB, recommended 4 GB and above storage space: minimum 250 MB, recommended 1 GB and above other requirements: stable network connection, Xorg/Wayland (Linux)

How to run java code in notepad How to run java code in notepad Apr 16, 2025 pm 07:39 PM

Although Notepad cannot run Java code directly, it can be achieved by using other tools: using the command line compiler (javac) to generate a bytecode file (filename.class). Use the Java interpreter (java) to interpret bytecode, execute the code, and output the result.

vscode cannot install extension vscode cannot install extension Apr 15, 2025 pm 07:18 PM

The reasons for the installation of VS Code extensions may be: network instability, insufficient permissions, system compatibility issues, VS Code version is too old, antivirus software or firewall interference. By checking network connections, permissions, log files, updating VS Code, disabling security software, and restarting VS Code or computers, you can gradually troubleshoot and resolve issues.

Linux Architecture: Unveiling the 5 Basic Components Linux Architecture: Unveiling the 5 Basic Components Apr 20, 2025 am 12:04 AM

The five basic components of the Linux system are: 1. Kernel, 2. System library, 3. System utilities, 4. Graphical user interface, 5. Applications. The kernel manages hardware resources, the system library provides precompiled functions, system utilities are used for system management, the GUI provides visual interaction, and applications use these components to implement functions.

How to use VSCode How to use VSCode Apr 15, 2025 pm 11:21 PM

Visual Studio Code (VSCode) is a cross-platform, open source and free code editor developed by Microsoft. It is known for its lightweight, scalability and support for a wide range of programming languages. To install VSCode, please visit the official website to download and run the installer. When using VSCode, you can create new projects, edit code, debug code, navigate projects, expand VSCode, and manage settings. VSCode is available for Windows, macOS, and Linux, supports multiple programming languages ​​and provides various extensions through Marketplace. Its advantages include lightweight, scalability, extensive language support, rich features and version

Can vscode be used for mac Can vscode be used for mac Apr 15, 2025 pm 07:36 PM

VS Code is available on Mac. It has powerful extensions, Git integration, terminal and debugger, and also offers a wealth of setup options. However, for particularly large projects or highly professional development, VS Code may have performance or functional limitations.

How to check the warehouse address of git How to check the warehouse address of git Apr 17, 2025 pm 01:54 PM

To view the Git repository address, perform the following steps: 1. Open the command line and navigate to the repository directory; 2. Run the "git remote -v" command; 3. View the repository name in the output and its corresponding address.

What is vscode What is vscode for? What is vscode What is vscode for? Apr 15, 2025 pm 06:45 PM

VS Code is the full name Visual Studio Code, which is a free and open source cross-platform code editor and development environment developed by Microsoft. It supports a wide range of programming languages ​​and provides syntax highlighting, code automatic completion, code snippets and smart prompts to improve development efficiency. Through a rich extension ecosystem, users can add extensions to specific needs and languages, such as debuggers, code formatting tools, and Git integrations. VS Code also includes an intuitive debugger that helps quickly find and resolve bugs in your code.

See all articles