change user mode value from kernel control path
Hi,
for a special purpose I need to read values in lxrt user mode which are changed in the kernel control path. To avoid expensive system calls I register the address of a user mode variable (int) with a new pointer in the task control path:
…
volatile int *tp_status;
…
}
To register the variable I introduced a new function in the api.c file:
{
RT_TASK *rt_current;
if (!access_ok(VERIFY_WRITE, address, size)) {
return -EINVAL;
}
rt_current = RT_CURRENT;
switch(variable) {
case RT_VAR_TP_STATUS:
rt_current->tp_status = (int *)address;
break;
…
}
In my user space program I use the following code to register the variable:
if (tp_status == NULL) {
return EANYTIME_INVAL;
}
if (mlock((const void *)tp_status, sizeof(const int )) < 0) {
return EANYTIME_MLOCK;
}
if (rt_register_v(RT_VAR_TP_STATUS, (void *)tp_status, sizeof(int)) < 0) {
return EANYTIME_INVAL;
}
return 0;
}
…..
I call the function with the following command:
…
anytime_assign_tp_status(&tp_status);
…
The registration works fine. In rt_schedule() I am able to access the user mode value with *(rt_current->tp_status). To chance the value from kernel control path I use the following line of code:
This also works fine. But after a lxrt_context_switch(prev, new_task->lnxtsk, cpuid); call in the rt_time_handler function the pointer new_task->tp_status points to the same user mode address but every access to user mode variable like *(new_task->tp_status) freeze the whole system? Furthermore sometimes it is possible to read the value of *(new_task->tp_status) and the content isn’t longer 1 or 3 - its 260348 for example. Does anybody knows the problem? I avoided swapping with the mlock call so why it is not longer possible to access the value after a context switch?
Best regards,
Nekoto
Categories
- 9.9K All Categories
- 29 LFX Mentorship
- 82 LFX Mentorship: Linux Kernel
- 465 Linux Foundation Boot Camps
- 266 Cloud Engineer Boot Camp
- 95 Advanced Cloud Engineer Boot Camp
- 43 DevOps Engineer Boot Camp
- 28 Cloud Native Developer Boot Camp
- 1 Express Training Courses
- 1 Express Courses - Discussion Forum
- 1.6K Training Courses
- 17 LFC110 Class Forum
- 3 LFC131 Class Forum
- 19 LFD102 Class Forum
- 127 LFD103 Class Forum
- 9 LFD121 Class Forum
- 59 LFD201 Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum
- 23 LFD254 Class Forum
- 544 LFD259 Class Forum
- 100 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 1 LFS145 Class Forum
- 20 LFS200 Class Forum
- 739 LFS201 Class Forum
- 1 LFS201-JP クラス フォーラム
- 1 LFS203 Class Forum
- 34 LFS207 Class Forum
- 294 LFS211 Class Forum
- 53 LFS216 Class Forum
- 45 LFS241 Class Forum
- 39 LFS242 Class Forum
- 33 LFS243 Class Forum
- 10 LFS244 Class Forum
- 27 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- 131 LFS253 Class Forum
- 959 LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 85 LFS260 Class Forum
- 124 LFS261 Class Forum
- 29 LFS262 Class Forum
- 78 LFS263 Class Forum
- 15 LFS264 Class Forum
- 10 LFS266 Class Forum
- 17 LFS267 Class Forum
- 16 LFS268 Class Forum
- 14 LFS269 Class Forum
- 193 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- 205 LFW211 Class Forum
- 148 LFW212 Class Forum
- 890 Hardware
- 212 Drivers
- 74 I/O Devices
- 44 Monitors
- 115 Multimedia
- 206 Networking
- 99 Printers & Scanners
- 85 Storage
- 747 Linux Distributions
- 88 Debian
- 64 Fedora
- 13 Linux Mint
- 13 Mageia
- 24 openSUSE
- 133 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 354 Ubuntu
- 468 Linux System Administration
- 38 Cloud Computing
- 67 Command Line/Scripting
- Github systems admin projects
- 93 Linux Security
- 77 Network Management
- 107 System Management
- 48 Web Management
- 61 Mobile Computing
- 22 Android
- 25 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 525 Off Topic
- 127 Introductions
- 211 Small Talk
- 19 Study Material
- 782 Programming and Development
- 256 Kernel Development
- 492 Software Development
- 919 Software
- 255 Applications
- 181 Command Line
- 2 Compiling/Installing
- 76 Games
- 316 Installation
- 46 All In Program
- 46 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)