MIPS: MT: Fix FPU affinity.

The fragile MT sys_sched_setaffinity wrapper needs its regular dose of
fixes.
Nose-poked-at-pile-o-crap-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/mips-mt-fpaff.c

@@ -3,6 +3,7 @@
  * Copyright (C) 2005 Mips Technologies, Inc
  */
 #include <linux/cpu.h>
+#include <linux/cpuset.h>
 #include <linux/cpumask.h>
 #include <linux/delay.h>
 #include <linux/kernel.h>
@@ -39,6 +40,21 @@ static inline struct task_struct *find_process_by_pid(pid_t pid)
 	return pid ? find_task_by_vpid(pid) : current;
 }
 
+/*
+ * check the target process has a UID that matches the current process's
+ */
+static bool check_same_owner(struct task_struct *p)
+{
+	const struct cred *cred = current_cred(), *pcred;
+	bool match;
+
+	rcu_read_lock();
+	pcred = __task_cred(p);
+	match = (cred->euid == pcred->euid ||
+		 cred->euid == pcred->uid);
+	rcu_read_unlock();
+	return match;
+}
 
 /*
  * mipsmt_sys_sched_setaffinity - set the cpu affinity of a process
@@ -46,12 +62,10 @@ static inline struct task_struct *find_process_by_pid(pid_t pid)
 asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len,
 				      unsigned long __user *user_mask_ptr)
 {
-	cpumask_t new_mask;
-	cpumask_t effective_mask;
-	int retval;
-	struct task_struct *p;
+	cpumask_var_t cpus_allowed, new_mask, effective_mask;
 	struct thread_info *ti;
-	uid_t euid;
+	struct task_struct *p;
+	int retval;
 
 	if (len < sizeof(new_mask))
 		return -EINVAL;
@@ -60,53 +74,74 @@ asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len,
 		return -EFAULT;
 
 	get_online_cpus();
-	read_lock(&tasklist_lock);
+	rcu_read_lock();
 
 	p = find_process_by_pid(pid);
 	if (!p) {
-		read_unlock(&tasklist_lock);
+		rcu_read_unlock();
 		put_online_cpus();
 		return -ESRCH;
 	}
 
-	/*
-	 * It is not safe to call set_cpus_allowed with the
-	 * tasklist_lock held.  We will bump the task_struct's
-	 * usage count and drop tasklist_lock before invoking
-	 * set_cpus_allowed.
-	 */
+	/* Prevent p going away */
 	get_task_struct(p);
+	rcu_read_unlock();
 
-	euid = current_euid();
+	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
+		retval = -ENOMEM;
+		goto out_put_task;
+	}
+	if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
+		retval = -ENOMEM;
+		goto out_free_cpus_allowed;
+	}
+	if (!alloc_cpumask_var(&effective_mask, GFP_KERNEL)) {
+		retval = -ENOMEM;
+		goto out_free_new_mask;
+	}
 	retval = -EPERM;
-	if (euid != p->cred->euid && euid != p->cred->uid &&
-	    !capable(CAP_SYS_NICE)) {
-		read_unlock(&tasklist_lock);
+	if (!check_same_owner(p) && !capable(CAP_SYS_NICE))
 		goto out_unlock;
-	}
 
 	retval = security_task_setscheduler(p, 0, NULL);
 	if (retval)
 		goto out_unlock;
 
 	/* Record new user-specified CPU set for future reference */
-	p->thread.user_cpus_allowed = new_mask;
-
-	/* Unlock the task list */
-	read_unlock(&tasklist_lock);
+	cpumask_copy(&p->thread.user_cpus_allowed, new_mask);
 
+ again:
 	/* Compute new global allowed CPU set if necessary */
 	ti = task_thread_info(p);
 	if (test_ti_thread_flag(ti, TIF_FPUBOUND) &&
-	    cpus_intersects(new_mask, mt_fpu_cpumask)) {
-		cpus_and(effective_mask, new_mask, mt_fpu_cpumask);
-		retval = set_cpus_allowed_ptr(p, &effective_mask);
+	    cpus_intersects(*new_mask, mt_fpu_cpumask)) {
+		cpus_and(*effective_mask, *new_mask, mt_fpu_cpumask);
+		retval = set_cpus_allowed_ptr(p, effective_mask);
 	} else {
+		cpumask_copy(effective_mask, new_mask);
 		clear_ti_thread_flag(ti, TIF_FPUBOUND);
-		retval = set_cpus_allowed_ptr(p, &new_mask);
+		retval = set_cpus_allowed_ptr(p, new_mask);
 	}
 
+	if (!retval) {
+		cpuset_cpus_allowed(p, cpus_allowed);
+		if (!cpumask_subset(effective_mask, cpus_allowed)) {
+			/*
+			 * We must have raced with a concurrent cpuset
+			 * update. Just reset the cpus_allowed to the
+			 * cpuset's cpus_allowed
+			 */
+			cpumask_copy(new_mask, cpus_allowed);
+			goto again;
+		}
+	}
 out_unlock:
+	free_cpumask_var(effective_mask);
+out_free_new_mask:
+	free_cpumask_var(new_mask);
+out_free_cpus_allowed:
+	free_cpumask_var(cpus_allowed);
+out_put_task:
 	put_task_struct(p);
 	put_online_cpus();
 	return retval;