Merge branches 'timers/clocksource', 'timers/hrtimers', 'timers/nohz', 'timers/ntp...

[linux-2.6-omap-h63xx.git] / kernel / exit.c

diff --git a/kernel/exit.c b/kernel/exit.c
index 40036ac04271a016d7946977f0e9655a33183566..059b38cae3848ea62fc7f03fb5a08c3dfbb53f10 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -580,8 +580,6 @@ mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
         * If there are other users of the mm and the owner (us) is exiting
         * we need to find a new owner to take on the responsibility.
         */
-       if (!mm)
-               return 0;
        if (atomic_read(&mm->mm_users) <= 1)
                return 0;
        if (mm->owner != p)
@@ -624,29 +622,38 @@ retry:
        } while_each_thread(g, c);
 
        read_unlock(&tasklist_lock);
+       /*
+        * We found no owner yet mm_users > 1: this implies that we are
+        * most likely racing with swapoff (try_to_unuse()) or /proc or
+        * ptrace or page migration (get_task_mm()).  Mark owner as NULL,
+        * so that subsystems can understand the callback and take action.
+        */
+       down_write(&mm->mmap_sem);
+       cgroup_mm_owner_callbacks(mm->owner, NULL);
+       mm->owner = NULL;
+       up_write(&mm->mmap_sem);
        return;
 
 assign_new_owner:
        BUG_ON(c == p);
        get_task_struct(c);
+       read_unlock(&tasklist_lock);
+       down_write(&mm->mmap_sem);
        /*
         * The task_lock protects c->mm from changing.
         * We always want mm->owner->mm == mm
         */
        task_lock(c);
-       /*
-        * Delay read_unlock() till we have the task_lock()
-        * to ensure that c does not slip away underneath us
-        */
-       read_unlock(&tasklist_lock);
        if (c->mm != mm) {
                task_unlock(c);
+               up_write(&mm->mmap_sem);
                put_task_struct(c);
                goto retry;
        }
        cgroup_mm_owner_callbacks(mm->owner, c);
        mm->owner = c;
        task_unlock(c);
+       up_write(&mm->mmap_sem);
        put_task_struct(c);
 }
 #endif /* CONFIG_MM_OWNER */