![[LWN Logo]](/images/lcorner.png) |
|
![[LWN.net]](/images/Included.png) |
From: Robert Love <rml@tech9.net>
To: linux-kernel@vger.kernel.org
Subject: [PATCH][RFC] task cpu affinity syscalls for 2.4-O(1)
Date: 22 Apr 2002 15:34:13 -0400
Following patch implements the 2.5 task affinity syscalls on top of the
2.4 O(1) scheduler patches I recently posted. We can implement these
now since 2.4's O(1) scheduler now has the migration_thread.
Previously, the 2.4 patches I did only worked on the "stock" scheduler.
I have a request for comments:
The locking is no good in this patch. set_cpus_allowed is not atomic
and it is certainly not safe to hold a spinlock across a call to it.
However, before we call set_cpus_allowed we need a valid reference to
the task and assurance the task won't slip away out from under us.
So you say "ah grab tasklist_lock" but we can't hold it across
set_cpus_allowed. In 2.5, we solve this by bumping the task_struct's
usage count via get_task_struct - this assures us at least the
task_struct will not go anywhere until we put_task_struct. We have no
such luxury in 2.4...
In this patch, we grab tasklist_lock. My testing isn't showing any
deadlocks, so feel free to play, but this approach is not safe.
Any ideas of a how to (a) assure a task is valid and will remain so
through a call to set_cpus_allowed, (b) do (a) without a spinlock?
Robert Love
diff -urN linux-O1/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S
--- linux-O1/arch/i386/kernel/entry.S Mon Apr 22 15:22:10 2002
+++ linux/arch/i386/kernel/entry.S Mon Apr 22 15:23:14 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-O1/include/linux/capability.h linux/include/linux/capability.h
--- linux-O1/include/linux/capability.h Mon Apr 22 15:21:46 2002
+++ linux/include/linux/capability.h Mon Apr 22 15:22:31 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-O1/kernel/sched.c linux/kernel/sched.c
--- linux-O1/kernel/sched.c Mon Apr 22 15:21:46 2002
+++ linux/kernel/sched.c Mon Apr 22 15:22:31 2002
@@ -1184,6 +1184,93 @@
return retval;
}
+/**
+ * sys_sched_setaffinity - set the cpu affinity of a process
+ * @pid: pid of the process
+ * @len: length in bytes of the mask pointed to by new_mask_ptr
+ * @new_mask: user-space pointer to the new cpu mask
+ */
+asmlinkage int sys_sched_setaffinity(pid_t pid, unsigned int len,
+ unsigned long *new_mask_ptr)
+{
+ unsigned long new_mask;
+ task_t *p;
+ int retval;
+
+ if (len < sizeof(new_mask))
+ return -EINVAL;
+
+ if (copy_from_user(&new_mask, new_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 mask pointed to by user_mask_ptr
+ * @user_mask_ptr: userspace pointer to the 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;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/