Revert "proc: don't allow async path resolution of /proc/self components"

stable inclusion
from stable-v5.10.162
commit b76c5373f084c802964e751efb825934a9bbbbec
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7P7OH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b76c5373f084c802964e751efb825934a9bbbbec

--------------------------------

[ Upstream commit 9e8d9e82 ]

This reverts commit 8d4c3e76.

No longer needed, as the io-wq worker threads have the right identity.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Nsanglipeng <sanglipeng1@jd.com>

fs/proc/self.c

@@ -16,13 +16,6 @@ static const char *proc_self_get_link(struct dentry *dentry,
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char *name;
 
-	/*
-	 * Not currently supported. Once we can inherit all of struct pid,
-	 * we can allow this.
-	 */
-	if (current->flags & PF_KTHREAD)
-		return ERR_PTR(-EOPNOTSUPP);
-
 	if (!tgid)
 		return ERR_PTR(-ENOENT);
 	/* max length of unsigned int in decimal + NULL term */