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tty: never hold BTM while getting tty_mutex 

tty_mutex is never taken with the BTM held, except for
two corner cases that are worked around here.
We give up the BTM before calling tty_release() in the
error path of tty_open().
Similarly, we reorder the locking in ptmx_open()
to get tty_mutex before the BTM.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Arnd Bergmann 2010-06-01 22:53:02 +02:00 committed by Greg Kroah-Hartman
parent ec79d6056d
commit 64ba3dc314
2 changed files with 17 additions and 19 deletions
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24
drivers/char/pty.c
View File

@ -647,7 +647,7 @@ static const struct tty_operations pty_unix98_ops = {
* allocated_ptys_lock handles the list of free pty numbers
*/
static int __ptmx_open(struct inode *inode, struct file *filp)
static int ptmx_open(struct inode *inode, struct file *filp)
{
struct tty_struct *tty;
int retval;
@ -656,11 +656,14 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
nonseekable_open(inode, filp);
/* find a device that is not in use. */
tty_lock();
index = devpts_new_index(inode);
tty_unlock();
if (index < 0)
return index;
mutex_lock(&tty_mutex);
tty_lock();
tty = tty_init_dev(ptm_driver, index, 1);
mutex_unlock(&tty_mutex);
@ -678,24 +681,19 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
goto out1;
retval = ptm_driver->ops->open(tty, filp);
if (!retval)
return 0;
if (retval)
goto out2;
out1:
tty_unlock();
return retval;
out2:
tty_unlock();
tty_release(inode, filp);
return retval;
out:
devpts_kill_index(inode, index);
return retval;
}
static int ptmx_open(struct inode *inode, struct file *filp)
{
int ret;
tty_lock();
ret = __ptmx_open(inode, filp);
tty_unlock();
return ret;
return retval;
}
static struct file_operations ptmx_fops;

12
drivers/char/tty_io.c
View File

@ -1866,19 +1866,19 @@ static int tty_open(struct inode *inode, struct file *filp)
printk(KERN_DEBUG "error %d in opening %s...", retval,
tty->name);
#endif
tty_unlock(); /* need to call tty_release without BTM */
tty_release(inode, filp);
if (retval != -ERESTARTSYS) {
tty_unlock();
if (retval != -ERESTARTSYS)
return retval;
}
if (signal_pending(current)) {
tty_unlock();
if (signal_pending(current))
return retval;
}
schedule();
/*
* Need to reset f_op in case a hangup happened.
*/
tty_lock();
if (filp->f_op == &hung_up_tty_fops)
filp->f_op = &tty_fops;
tty_unlock();