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Subject[PATCH 06/13] tty: never hold BTM while getting tty_mutex
Date
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>
---
drivers/char/pty.c | 22 ++++++++--------------
drivers/char/tty_io.c | 13 +++++++------
2 files changed, 15 insertions(+), 20 deletions(-)
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index dbb144b..889de89 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -626,7 +626,7 @@ 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;
@@ -635,11 +635,14 @@ 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);

@@ -657,24 +660,15 @@ 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)
+ tty_release(inode, filp);
out1:
- tty_release(inode, filp);
+ tty_unlock();
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;
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 82c723a..e1b2fca 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1871,21 +1871,22 @@ got_driver:
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();
goto retry_open;
}
tty_unlock();
--
1.7.0.4


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