Messages in this thread Patch in this message | | | Subject | [PATCH][RFC] 2.4-ac affinity syscalls and how to pin a task? | From | Robert Love <> | Date | 29 Apr 2002 14:39:30 -0400 |
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The attached patch implements the task cpu affinity interface on top of the O(1) scheduler in 2.4.19-pre7-ac3. The migration_thread is now in -ac3 so we can implement such an interface.
This is the same interface as in 2.5 and posted previously for 2.4 (sans O(1)):
sched_getaffinity(pid_t pid, unsigned long len, unsigned long *mask) sched_setaffinity(pid_t pid, unsigned long len, unsigned long *mask)
Problem:
We need to assure the task stays valid and does not exit, but due to the semantics of set_cpus_allowed and migration_thread we can not hold a lock across a call. In 2.5 we can pin a task via get_task_struct. This assures us, at least, that the task struct is not deallocated until a final call to put_task_struct.
What equivalent mechanism do we have in 2.4? How can we assure a task stays put without grabbing a spinlock?
This patch grabs the tasklist_lock before calling set_cpus_allowed. While this is working fine here and is safe enough to play with now, it is not safe.
Comments?
Robert Love
diff -urN linux-2.4.19-pre7-ac3/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S --- linux-2.4.19-pre7-ac3/arch/i386/kernel/entry.S Mon Apr 29 12:34:58 2002 +++ linux/arch/i386/kernel/entry.S Mon Apr 29 14:29:32 2002 @@ -639,8 +639,8 @@ .long SYMBOL_NAME(sys_tkill) .long SYMBOL_NAME(sys_ni_syscall) /* reserved for sendfile64 */ .long SYMBOL_NAME(sys_ni_syscall) /* 240 reserved for futex */ - .long SYMBOL_NAME(sys_ni_syscall) /* reserved for sched_setaffinity */ - .long SYMBOL_NAME(sys_ni_syscall) /* reserved for sched_getaffinity */ + .long SYMBOL_NAME(sys_sched_setaffinity) + .long SYMBOL_NAME(sys_sched_getaffinity) .rept NR_syscalls-(.-sys_call_table)/4 .long SYMBOL_NAME(sys_ni_syscall) diff -urN linux-2.4.19-pre7-ac3/include/linux/capability.h linux/include/linux/capability.h --- linux-2.4.19-pre7-ac3/include/linux/capability.h Mon Apr 29 12:33:28 2002 +++ linux/include/linux/capability.h Mon Apr 29 14:29:32 2002 @@ -243,6 +243,7 @@ /* Allow use of FIFO and round-robin (realtime) scheduling on own processes and setting the scheduling algorithm used by another process. */ +/* Allow setting cpu affinity on other processes */ #define CAP_SYS_NICE 23 diff -urN linux-2.4.19-pre7-ac3/kernel/sched.c linux/kernel/sched.c --- linux-2.4.19-pre7-ac3/kernel/sched.c Mon Apr 29 12:33:23 2002 +++ linux/kernel/sched.c Mon Apr 29 14:33:49 2002 @@ -1183,6 +1183,93 @@ return retval; } +/** + * sys_sched_setaffinity - set the cpu affinity of a process + * @pid: pid of the process + * @len: length in bytes of the bitmask pointed to by user_mask_ptr + * @user_mask_ptr: user-space pointer to the new cpu mask + */ +asmlinkage int sys_sched_setaffinity(pid_t pid, unsigned int len, + unsigned long *user_mask_ptr) +{ + unsigned long new_mask; + task_t *p; + int retval; + + if (len < sizeof(new_mask)) + return -EINVAL; + + if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask))) + return -EFAULT; + + new_mask &= cpu_online_map; + if (!new_mask) + return -EINVAL; + + /* + * FIXME: It is unsafe to call set_cpus_allowed while + * holding a lock. In 2.5, we can bump the task_struct's + * usage count - for 2.4, we have no such luxury. Holding + * tasklist_lock here is a temporary hack. You are warned. + */ + write_lock(&tasklist_lock); + + retval = -ESRCH; + p = find_process_by_pid(pid); + if (!p) + goto out_unlock; + + retval = -EPERM; + if ((current->euid != p->euid) && (current->euid != p->uid) && + !capable(CAP_SYS_NICE)) + goto out_unlock; + + retval = 0; + set_cpus_allowed(p, new_mask); + +out_unlock: + write_unlock(&tasklist_lock); + return retval; +} + +/** + * sys_sched_getaffinity - get the cpu affinity of a process + * @pid: pid of the process + * @len: length in bytes of the bitmask pointed to by user_mask_ptr + * @user_mask_ptr: user-space pointer to hold the current cpu mask + */ +asmlinkage int sys_sched_getaffinity(pid_t pid, unsigned int len, + unsigned long *user_mask_ptr) +{ + unsigned long mask; + unsigned int real_len; + task_t *p; + int retval; + + real_len = sizeof(mask); + + if (len < real_len) + return -EINVAL; + + read_lock(&tasklist_lock); + + retval = -ESRCH; + p = find_process_by_pid(pid); + if (!p) + goto out_unlock; + + retval = 0; + mask = p->cpus_allowed & cpu_online_map; + +out_unlock: + read_unlock(&tasklist_lock); + if (retval) + return retval; + if (copy_to_user(user_mask_ptr, &mask, real_len)) + return -EFAULT; + return real_len; +} + asmlinkage long sys_sched_yield(void) { runqueue_t *rq;
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