concurrency - Linux内核如何处理并发文件查找

Question

假设有两个进程同时查找一个文件，而这个文件在 dcache 中还不存在。这两个查找将向进程返回 NULL ( dentry )。

我的问题是，Linux 内核如何确保在失败的 dentry 查找之后，它只创建一个 dentry？

Answer 1

1912 /**
1913  * d_lookup - search for a dentry
1914  * @parent: parent dentry
1915  * @name: qstr of name we wish to find
1916  * Returns: dentry, or NULL
1917  *
1918  * d_lookup searches the children of the parent dentry for the name in
1919  * question. If the dentry is found its reference count is incremented and the
1920  * dentry is returned. The caller must use dput to free the entry when it has
1921  * finished using it. %NULL is returned if the dentry does not exist.
1922  */

d_lookup不会dentry自己创建任何对象。看一下do_filp_open逻辑，它显示了如何dentries创建。