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>

1 files changed, 61 insertions, 26 deletions

diff --git a/arch/mips/kernel/mips-mt-fpaff.c b/arch/mips/kernel/mips-mt-fpaff.c
index f5981c499109..2340f11dc29c 100644
--- a/arch/mips/kernel/mips-mt-fpaff.c
+++ b/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;