[PATCH] mm: migrate: simplify find_mm_struct()

[Nanyong Sun]

Use find_get_task_by_vpid() to replace the task_struct find logic in
find_mm_struct(), note that this patch move the ptrace_may_access()
call out from rcu_read_lock() scope, this is ok because it actually
does not need it, find_get_task_by_vpid() already get the pid and task
safely, ptrace_may_access() can use the task safely, like what
sched_core_share_pid() similarly do.

Signed-off-by: Nanyong Sun <sunnanyong@xxxxxxxxxx>
---
 mm/migrate.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 923ea80ba744..e9477c64c267 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2432,25 +2432,19 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes)
 		return current->mm;
 	}
 
-	/* Find the mm_struct */
-	rcu_read_lock();
-	task = find_task_by_vpid(pid);
+	task = find_get_task_by_vpid(pid);
 	if (!task) {
-		rcu_read_unlock();
 		return ERR_PTR(-ESRCH);
 	}
-	get_task_struct(task);
 
 	/*
 	 * Check if this process has the right to modify the specified
 	 * process. Use the regular "ptrace_may_access()" checks.
 	 */
 	if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
-		rcu_read_unlock();
 		mm = ERR_PTR(-EPERM);
 		goto out;
 	}
-	rcu_read_unlock();
 
 	mm = ERR_PTR(security_task_movememory(task));
 	if (IS_ERR(mm))
-- 
2.33.0