Messages in this thread Patch in this message | | | Date | Wed, 27 Mar 2002 14:59:13 -0600 | From | Stephen Baker <> | Subject | Linux Kernel Patch; setpriority |
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All,
This patch will allow a process or thread to changes it's priority dynamically based on it's capabilities. In our case we wanted to use threads with Linux. To have true priorities we need root to use SCHED_FIFO or SCHED_RR; in many case root access is not allowed but we still wanted priorities. So we started using setpriority to change a threads priority. Now we used nice values from 19 to 0 which did not require root access. In some cases a thread need to raise it's nice level and this would fail. I also saw a note man renice(8) that said this bug exists. So the following patch address this problem. It allows any process or thread to raise or lower it's nice value for it's current capability. For example a CAP_SYS_NICE process can use 19 to -20 for it's value and a normal user can use 19 to 0. By capping normal user to zero then we don't have any problems with conflicts with higher priority programs in the system since zero is the default value.
SB
--- linux-2.4.9-31/kernel/sys.c Wed Mar 27 13:11:10 2002 +++ linux/kernel/sys.c Wed Mar 27 13:09:36 2002 @@ -194,6 +194,12 @@ return 0; }
+/* + * Allow the process to adjust it's priority higher or lower. + * If the process has CAP_SYS_NICE set then we can use + * -20 to 19. Otherwise we use 0 to 19 as our valid priority + * range. + */ asmlinkage long sys_setpriority(int which, int who, int niceval) { struct task_struct *p; @@ -220,7 +226,8 @@ } if (error == -ESRCH) error = 0; - if (niceval < p->nice && !capable(CAP_SYS_NICE)) + if ((niceval < 0) && + (niceval < p->nice && !capable(CAP_SYS_NICE))) error = -EACCES; else p->nice = niceval;
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