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From: Greg Kroah-Hartman on 10 Aug 2010 18:10
From: Arnd Bergmann <arnd(a)arndb.de>

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(a)arndb.de>
Cc: Alan Cox <alan(a)lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>
---
drivers/char/pty.c | 24 +++++++++++-------------
drivers/char/tty_io.c | 12 ++++++------
2 files changed, 17 insertions(+), 19 deletions(-)

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 622e21c..de22ea9 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -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;
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 5ee9081..bb22cf4 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1866,19 +1866,19 @@ 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();
--
1.7.2

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Prev: [PATCH 31/68] serial: add port helpers
Next: [PATCH 68/68] U6715 16550A serial driver support