pidfs: remove pidfs_{get,put}_pid()

Now that we stash persistent information in struct pid there's no need
to play volatile games with pinning struct pid via dentries in pidfs.

Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-8-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/coredump.c

@@ -898,12 +898,6 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 		retval = kernel_connect(socket, (struct sockaddr *)(&addr),
 					addr_len, O_NONBLOCK | SOCK_COREDUMP);
 
-		/*
-		 * ... Make sure to only put our reference after connect() took
-		 * its own reference keeping the pidfs entry alive ...
-		 */
-		pidfs_put_pid(cprm.pid);
-
 		if (retval) {
 			if (retval == -EAGAIN)
 				coredump_report_failure("Coredump socket %s receive queue full", addr.sun_path);

fs/pidfs.c

@@ -895,8 +895,7 @@ static void pidfs_put_data(void *data)
  * pidfs_register_pid - register a struct pid in pidfs
  * @pid: pid to pin
  *
- * Register a struct pid in pidfs. Needs to be paired with
- * pidfs_put_pid() to not risk leaking the pidfs dentry and inode.
+ * Register a struct pid in pidfs.
  *
  * Return: On success zero, on error a negative error code is returned.
  */
@@ -1007,38 +1006,6 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
 	return pidfd_file;
 }
 
-/**
- * pidfs_get_pid - pin a struct pid through pidfs
- * @pid: pid to pin
- *
- * Similar to pidfs_register_pid() but only valid if the caller knows
- * there's a reference to the @pid through a dentry already that can't
- * go away.
- */
-void pidfs_get_pid(struct pid *pid)
-{
-	if (!pid)
-		return;
-	WARN_ON_ONCE(!stashed_dentry_get(&pid->stashed));
-}
-
-/**
- * pidfs_put_pid - drop a pidfs reference
- * @pid: pid to drop
- *
- * Drop a reference to @pid via pidfs. This is only safe if the
- * reference has been taken via pidfs_get_pid().
- */
-void pidfs_put_pid(struct pid *pid)
-{
-	might_sleep();
-
-	if (!pid)
-		return;
-	VFS_WARN_ON_ONCE(!pid->stashed);
-	dput(pid->stashed);
-}
-
 void __init pidfs_init(void)
 {
 	pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0,

include/linux/pidfs.h

@@ -14,8 +14,6 @@ void pidfs_coredump(const struct coredump_params *cprm);
 #endif
 extern const struct dentry_operations pidfs_dentry_operations;
 int pidfs_register_pid(struct pid *pid);
-void pidfs_get_pid(struct pid *pid);
-void pidfs_put_pid(struct pid *pid);
 void pidfs_free_pid(struct pid *pid);
 
 #endif /* _LINUX_PID_FS_H */

net/unix/af_unix.c

@@ -646,9 +646,6 @@ static void unix_sock_destructor(struct sock *sk)
 		return;
 	}
 
-	if (sk->sk_peer_pid)
-		pidfs_put_pid(sk->sk_peer_pid);
-
 	if (u->addr)
 		unix_release_addr(u->addr);
 
@@ -769,7 +766,6 @@ static void drop_peercred(struct unix_peercred *peercred)
 	swap(peercred->peer_pid, pid);
 	swap(peercred->peer_cred, cred);
 
-	pidfs_put_pid(pid);
 	put_pid(pid);
 	put_cred(cred);
 }
@@ -802,7 +798,6 @@ static void copy_peercred(struct sock *sk, struct sock *peersk)
 
 	spin_lock(&sk->sk_peer_lock);
 	sk->sk_peer_pid = get_pid(peersk->sk_peer_pid);
-	pidfs_get_pid(sk->sk_peer_pid);
 	sk->sk_peer_cred = get_cred(peersk->sk_peer_cred);
 	spin_unlock(&sk->sk_peer_lock);
 }