!1163 [sync] PR-1098: proc: allow pid_revalidate() during LOOKUP_RCU

Merge Pull Request from: @openeuler-sync-bot 
 

Origin pull request: 
https://gitee.com/openeuler/kernel/pulls/1098 
 
PR sync from:  Li Nan <linan122@huawei.com>
 https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/thread/4EEIPQOJKUZAK6RIRH5RREOILH6ZD3EC/ 
 
 
Link:https://gitee.com/openeuler/kernel/pulls/1163 

Reviewed-by: zhangyi (F) <yi.zhang@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

fs/proc/base.c

@@ -2100,19 +2100,21 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags)
 {
 	struct inode *inode;
 	struct task_struct *task;
+	int ret = 0;
 
-	if (flags & LOOKUP_RCU)
-		return -ECHILD;
-
-	inode = d_inode(dentry);
-	task = get_proc_task(inode);
+	rcu_read_lock();
+	inode = d_inode_rcu(dentry);
+	if (!inode)
+		goto out;
+	task = pid_task(proc_pid(inode), PIDTYPE_PID);
 
 	if (task) {
 		pid_update_inode(task, inode);
-		put_task_struct(task);
-		return 1;
+		ret = 1;
 	}
-	return 0;
+out:
+	rcu_read_unlock();
+	return ret;
 }
 
 static inline bool proc_inode_is_dead(struct inode *inode)