Revert "pty: fix the cached path of the pty slave file descriptor in the master" (143c97cc) · Commits · 戴 / test

This reverts commit . It turns out that while fixing the ptmx file descriptor to have the correct 'struct path' to the associated slave pty is a really good thing, it breaks some user space tools for a very annoying reason. The problem is that /dev/ptmx and its associated slave pty (/dev/pts/X) are on different mounts. That was what caused us to have the wrong path in the first place (we would mix up the vfsmount of the 'ptmx' node, with the dentry of the pty slave node), but it also means that now while we use the right vfsmount, having the pty master open also keeps the pts mount busy. And it turn sout that that makes 'pbuilder' very unhappy, as noted by Stefan Lippers-Hollmann: "This patch introduces a regression for me when using pbuilder 0.228.7[2] (a helper to build Debian packages in a chroot and to create and update its chroots) when trying to umount /dev/ptmx (inside the chroot) on Debian/ unstable (full log and pbuilder configuration file[3] attached). [...] Setting up build-essential (12.3) ... Processing triggers for libc-bin (2.24-15) ... I: unmounting dev/ptmx filesystem W: Could not unmount dev/ptmx: umount: /var/cache/pbuilder/build/1340/dev/ptmx: target is busy (In some cases useful info about processes that use the device is found by lsof(8) or fuser(1).)" apparently pbuilder tries to unmount the /dev/pts filesystem while still holding at least one master node open, which is arguably not very nice, but we don't break user space even when fixing other bugs. So this commit has to be reverted. I'll try to figure out a way to avoid caching the path to the slave pty in the master pty. The only thing that actually wants that slave pty path is the "TIOCGPTPEER" ioctl, and I think we could just recreate the path at that time. Reported-by:

Stefan Lippers-Hollmann <s.l-h@gmx.de> Cc: Eric W Biederman <ebiederm@xmission.com> Cc: Christian Brauner <christian.brauner@canonical.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

drivers/tty/pty.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -793,7 +793,6 @@ static int ptmx_open(struct inode inode, struct file filp)
		struct tty_struct *tty;
		struct path *pts_path;
		struct dentry *dentry;
		struct vfsmount *mnt;
		int retval;
		int index;

		@@ -806,7 +805,7 @@ static int ptmx_open(struct inode inode, struct file filp)
		if (retval)
		return retval;

		fsi = devpts_acquire(filp, &mnt);
		fsi = devpts_acquire(filp);
		if (IS_ERR(fsi)) {
		retval = PTR_ERR(fsi);
		goto out_free_file;
		@@ -850,7 +849,7 @@ static int ptmx_open(struct inode inode, struct file filp)
		pts_path = kmalloc(sizeof(struct path), GFP_KERNEL);
		if (!pts_path)
		goto err_release;
		pts_path->mnt = mnt;
		pts_path->mnt = filp->f_path.mnt;
		pts_path->dentry = dentry;
		path_get(pts_path);
		tty->link->driver_data = pts_path;
		@@ -867,7 +866,6 @@ err_path_put:
		path_put(pts_path);
		kfree(pts_path);
		err_release:
		mntput(mnt);
		tty_unlock(tty);
		// This will also put-ref the fsi
		tty_release(inode, filp);
		@@ -876,7 +874,6 @@ out:
		devpts_kill_index(fsi, index);
		out_put_fsi:
		devpts_release(fsi);
		mntput(mnt);
		out_free_file:
		tty_free_file(filp);
		return retval;

fs/devpts/inode.c

+1 −3

Original line number	Diff line number	Diff line
		@@ -133,7 +133,7 @@ static inline struct pts_fs_info DEVPTS_SB(struct super_block sb)
		return sb->s_fs_info;
		}

		struct pts_fs_info devpts_acquire(struct file filp, struct vfsmount **ptsmnt)
		struct pts_fs_info devpts_acquire(struct file filp)
		{
		struct pts_fs_info *result;
		struct path path;
		@@ -142,7 +142,6 @@ struct pts_fs_info devpts_acquire(struct file filp, struct vfsmount **ptsmnt)

		path = filp->f_path;
		path_get(&path);
		*ptsmnt = NULL;

		/* Has the devpts filesystem already been found? */
		sb = path.mnt->mnt_sb;
		@@ -166,7 +165,6 @@ struct pts_fs_info devpts_acquire(struct file filp, struct vfsmount **ptsmnt)
		* pty code needs to hold extra references in case of last /dev/tty close
		*/
		atomic_inc(&sb->s_active);
		*ptsmnt = mntget(path.mnt);
		result = DEVPTS_SB(sb);

		out:

include/linux/devpts_fs.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -19,7 +19,7 @@

		struct pts_fs_info;

		struct pts_fs_info devpts_acquire(struct file , struct vfsmount **ptsmnt);
		struct pts_fs_info devpts_acquire(struct file );
		void devpts_release(struct pts_fs_info *);

		int devpts_new_index(struct pts_fs_info *);

Admin message