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Message-ID: <20070129181235.GA9063@lst.de>
Date: Mon, 29 Jan 2007 19:12:35 +0100
From: Christoph Hellwig <hch@....de>
To: Alan Cox <alan@...hat.com>
Cc: Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: cleanup release_mem
On Mon, Jan 29, 2007 at 07:01:00AM -0500, Alan Cox wrote:
> On Sun, Jan 28, 2007 at 06:12:44PM +0100, Christoph Hellwig wrote:
> > release_mem contains two copies of exactly the same code. Refactor
> > these into a new helper, release_tty. The only change in behaviour
> > is that the driver reference count is now decremented after the
> > master tty has been freed instead of before.
> >
> >
> > Signed-off-by: Christoph Hellwig <hch@....de>
>
> Acked-by: Alan Cox <alan@...hat.com>
>
> Please propogate the mutex_ FIXME comment to both functions as it may
> well need to cover tty->link
Okay. Now that we get into the details I've also added some renaming,
release_mem becomes release_tty and the new factored out function is
release_one_tty. The difference is documented in the kdoc comments.
Signed-off-by: Christoph Hellwig <hch@....de>
Index: linux-2.6/drivers/char/tty_io.c
===================================================================
--- linux-2.6.orig/drivers/char/tty_io.c 2007-01-29 10:01:46.000000000 +0100
+++ linux-2.6/drivers/char/tty_io.c 2007-01-29 19:08:06.000000000 +0100
@@ -154,7 +154,7 @@
int tty_ioctl(struct inode * inode, struct file * file,
unsigned int cmd, unsigned long arg);
static int tty_fasync(int fd, struct file * filp, int on);
-static void release_mem(struct tty_struct *tty, int idx);
+static void release_tty(struct tty_struct *tty, int idx);
/**
* alloc_tty_struct - allocate a tty object
@@ -2003,7 +2003,7 @@
/*
* All structures have been allocated, so now we install them.
- * Failures after this point use release_mem to clean up, so
+ * Failures after this point use release_tty to clean up, so
* there's no need to null out the local pointers.
*/
if (!(driver->flags & TTY_DRIVER_DEVPTS_MEM)) {
@@ -2024,8 +2024,8 @@
/*
* Structures all installed ... call the ldisc open routines.
- * If we fail here just call release_mem to clean up. No need
- * to decrement the use counts, as release_mem doesn't care.
+ * If we fail here just call release_tty to clean up. No need
+ * to decrement the use counts, as release_tty doesn't care.
*/
if (tty->ldisc.open) {
@@ -2095,17 +2095,17 @@
retval = -ENOMEM;
goto end_init;
- /* call the tty release_mem routine to clean out this slot */
+ /* call the tty release_tty routine to clean out this slot */
release_mem_out:
if (printk_ratelimit())
printk(KERN_INFO "init_dev: ldisc open failed, "
"clearing slot %d\n", idx);
- release_mem(tty, idx);
+ release_tty(tty, idx);
goto end_init;
}
/**
- * release_mem - release tty structure memory
+ * release_one_tty - release tty structure memory
*
* Releases memory associated with a tty structure, and clears out the
* driver table slots. This function is called when a device is no longer
@@ -2117,37 +2117,14 @@
* of ttys that the driver keeps.
* FIXME: should we require tty_mutex is held here ??
*/
-
-static void release_mem(struct tty_struct *tty, int idx)
+static void release_one_tty(struct tty_struct *tty, int idx)
{
- struct tty_struct *o_tty;
- struct ktermios *tp;
int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;
-
- if ((o_tty = tty->link) != NULL) {
- if (!devpts)
- o_tty->driver->ttys[idx] = NULL;
- if (o_tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
- tp = o_tty->termios;
- if (!devpts)
- o_tty->driver->termios[idx] = NULL;
- kfree(tp);
-
- tp = o_tty->termios_locked;
- if (!devpts)
- o_tty->driver->termios_locked[idx] = NULL;
- kfree(tp);
- }
- o_tty->magic = 0;
- o_tty->driver->refcount--;
- file_list_lock();
- list_del_init(&o_tty->tty_files);
- file_list_unlock();
- free_tty_struct(o_tty);
- }
+ struct ktermios *tp;
if (!devpts)
tty->driver->ttys[idx] = NULL;
+
if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
tp = tty->termios;
if (!devpts)
@@ -2160,15 +2137,37 @@
kfree(tp);
}
+
tty->magic = 0;
tty->driver->refcount--;
+
file_list_lock();
list_del_init(&tty->tty_files);
file_list_unlock();
- module_put(tty->driver->owner);
+
free_tty_struct(tty);
}
+/**
+ * release_one_tty - release tty structure memory
+ *
+ * Release both @tty and a possible linked partner (think pty pair),
+ * and decrement the refcount of the backing module.
+ *
+ * Locking:
+ * tty_mutex - sometimes only
+ * takes the file list lock internally when working on the list
+ * of ttys that the driver keeps.
+ * FIXME: should we require tty_mutex is held here ??
+ */
+static void release_tty(struct tty_struct *tty, int idx)
+{
+ if (tty->link)
+ release_one_tty(tty->link, idx);
+ release_one_tty(tty, idx);
+ module_put(tty->driver->owner);
+}
+
/*
* Even releasing the tty structures is a tricky business.. We have
* to be very careful that the structures are all released at the
@@ -2436,10 +2435,10 @@
tty_set_termios_ldisc(o_tty,N_TTY);
}
/*
- * The release_mem function takes care of the details of clearing
+ * The release_tty function takes care of the details of clearing
* the slots and preserving the termios structure.
*/
- release_mem(tty, idx);
+ release_tty(tty, idx);
#ifdef CONFIG_UNIX98_PTYS
/* Make this pty number available for reallocation */
-
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