Re: [PATCH 0/1] devpts: use dynamic_dname() to generate proc name

Linus Torvalds
2017-08-16T21:03:16Z

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On Wed, Aug 16, 2017 at 1:30 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I suspect the easiest fix is to just add a "mnt" argument to
> devpts_acquire(), It shouldn't be too painful. Let me try.

Ok, here's a *very* lightly tested patch. It might have new bugs, but
it makes your test program DTRT.

Al, mind going over this and making sure I didn't miss anything?

And Christian, if you can beat on this, that would be good.

Linus

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drivers/tty/pty.c | 15 +++++++++++----
fs/devpts/inode.c | 4 +++-
include/linux/devpts_fs.h | 2 +-
3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 284749fb0f6b..432f514e3f42 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -793,6 +793,7 @@ 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;

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

- fsi = devpts_acquire(filp);
+ fsi = devpts_acquire(filp, &mnt);
if (IS_ERR(fsi)) {
retval = PTR_ERR(fsi);
goto out_free_file;
@@ -849,9 +850,14 @@ 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 = filp->f_path.mnt;
- pts_path->dentry = dentry;
- path_get(pts_path);
+
+ /*
+ * The mnt already got a ref from devpts_acquire(),
+ * so we only dget() on the dentry.
+ */
+ pts_path->mnt = mnt;
+ pts_path->dentry = dget(dentry);
+
tty->link->driver_data = pts_path;

retval = ptm_driver->ops->open(tty, filp);
@@ -874,6 +880,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
devpts_kill_index(fsi, index);
out_put_fsi:
devpts_release(fsi);
+ mntput(mnt);
out_free_file:
tty_free_file(filp);
return retval;
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 108df2e3602c..44dfbca9306f 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -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 pts_fs_info *devpts_acquire(struct file *filp, struct vfsmount **ptsmnt)
{
struct pts_fs_info *result;
struct path path;
@@ -142,6 +142,7 @@ struct pts_fs_info *devpts_acquire(struct file *filp)

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

/* Has the devpts filesystem already been found? */
sb = path.mnt->mnt_sb;
@@ -165,6 +166,7 @@ struct pts_fs_info *devpts_acquire(struct file *filp)
* 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:
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 277ab9af9ac2..7883e901f65c 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -19,7 +19,7 @@

struct pts_fs_info;

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

int devpts_new_index(struct pts_fs_info *);