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

This changes all remaining users of tty_lock_nested
to be non-recursive, which lets us kill this function.
As a consequence, we won't need to keep the lock count
any more, which allows more simplifications later.

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 | 2 +-
drivers/char/selection.c | 4 ++--
drivers/char/tty_io.c | 41 ++++++++++++++++++++---------------------
drivers/char/tty_ldisc.c | 3 +--
include/linux/tty.h | 16 +---------------
5 files changed, 25 insertions(+), 41 deletions(-)

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index de22ea9..f2d7a76 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -62,7 +62,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
if (tty->driver == ptm_driver)
devpts_pty_kill(tty->link);
#endif
- tty_vhangup(tty->link);
+ tty_vhangup_locked(tty->link);
}
}

diff --git a/drivers/char/selection.c b/drivers/char/selection.c
index 75889cd..ebae344 100644
--- a/drivers/char/selection.c
+++ b/drivers/char/selection.c
@@ -313,7 +313,8 @@ int paste_selection(struct tty_struct *tty)
struct tty_ldisc *ld;
DECLARE_WAITQUEUE(wait, current);

- tty_lock_nested(); /* always called with BTM from vt_ioctl */
+ /* always called with BTM from vt_ioctl */
+ WARN_ON(!tty_locked());

acquire_console_sem();
poke_blanked_console();
@@ -343,6 +344,5 @@ int paste_selection(struct tty_struct *tty)
__set_current_state(TASK_RUNNING);

tty_ldisc_deref(ld);
- tty_unlock();
return 0;
}
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index bb22cf4..dcf7d36 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -492,10 +492,8 @@ EXPORT_SYMBOL_GPL(tty_wakeup);
* tasklist_lock to walk task list for hangup event
* ->siglock to protect ->signal/->sighand
*/
-static void do_tty_hangup(struct work_struct *work)
+void tty_vhangup_locked(struct tty_struct *tty)
{
- struct tty_struct *tty =
- container_of(work, struct tty_struct, hangup_work);
struct file *cons_filp = NULL;
struct file *filp, *f = NULL;
struct task_struct *p;
@@ -517,8 +515,6 @@ static void do_tty_hangup(struct work_struct *work)
/* inuse_filps is protected by the single tty lock,
this really needs to change if we want to flush the
workqueue with the lock held */
- tty_lock_nested(); /* called with BTM held from pty_close and
- others */
check_tty_count(tty, "do_tty_hangup");

file_list_lock();
@@ -598,11 +594,20 @@ static void do_tty_hangup(struct work_struct *work)
*/
set_bit(TTY_HUPPED, &tty->flags);
tty_ldisc_enable(tty);
- tty_unlock();
if (f)
fput(f);
}

+static void do_tty_hangup(struct work_struct *work)
+{
+ struct tty_struct *tty =
+ container_of(work, struct tty_struct, hangup_work);
+
+ tty_lock();
+ tty_vhangup_locked(tty);
+ tty_unlock();
+}
+
/**
* tty_hangup - trigger a hangup event
* @tty: tty to hangup
@@ -638,7 +643,9 @@ void tty_vhangup(struct tty_struct *tty)

printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf));
#endif
- do_tty_hangup(&tty->hangup_work);
+ tty_lock();
+ tty_vhangup_locked(tty);
+ tty_unlock();
}

EXPORT_SYMBOL(tty_vhangup);
@@ -719,10 +726,12 @@ void disassociate_ctty(int on_exit)
tty = get_current_tty();
if (tty) {
tty_pgrp = get_pid(tty->pgrp);
- tty_lock_nested(); /* see above */
- if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
- tty_vhangup(tty);
- tty_unlock();
+ if (on_exit) {
+ tty_lock();
+ if (tty->driver->type != TTY_DRIVER_TYPE_PTY)
+ tty_vhangup_locked(tty);
+ tty_unlock();
+ }
tty_kref_put(tty);
} else if (on_exit) {
struct pid *old_pgrp;
@@ -1213,18 +1222,14 @@ static int tty_driver_install_tty(struct tty_driver *driver,
int ret;

if (driver->ops->install) {
- tty_lock_nested(); /* already called with BTM held */
ret = driver->ops->install(driver, tty);
- tty_unlock();
return ret;
}

if (tty_init_termios(tty) == 0) {
- tty_lock_nested();
tty_driver_kref_get(driver);
tty->count++;
driver->ttys[idx] = tty;
- tty_unlock();
return 0;
}
return -ENOMEM;
@@ -1317,15 +1322,11 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
struct tty_struct *tty;
int retval;

- tty_lock_nested(); /* always called with tty lock held already */
-
/* Check if pty master is being opened multiple times */
if (driver->subtype == PTY_TYPE_MASTER &&
(driver->flags & TTY_DRIVER_DEVPTS_MEM) && !first_ok) {
- tty_unlock();
return ERR_PTR(-EIO);
}
- tty_unlock();

/*
* First time open is complex, especially for PTY devices.
@@ -1369,9 +1370,7 @@ release_mem_out:
if (printk_ratelimit())
printk(KERN_INFO "tty_init_dev: ldisc open failed, "
"clearing slot %d\n", idx);
- tty_lock_nested();
release_tty(tty, idx);
- tty_unlock();
return ERR_PTR(retval);
}

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index 0f49479..412f977 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -450,9 +450,8 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
if (ld->ops->open) {
int ret;
/* BTM here locks versus a hangup event */
- tty_lock_nested(); /* always held here already */
+ WARN_ON(!tty_locked());
ret = ld->ops->open(tty);
- tty_unlock();
return ret;
}
return 0;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 955d72e..0fbafb0 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -417,6 +417,7 @@ extern int is_ignored(int sig);
extern int tty_signal(int sig, struct tty_struct *tty);
extern void tty_hangup(struct tty_struct *tty);
extern void tty_vhangup(struct tty_struct *tty);
+extern void tty_vhangup_locked(struct tty_struct *tty);
extern void tty_vhangup_self(void);
extern void tty_unhangup(struct file *filp);
extern int tty_hung_up_p(struct file *filp);
@@ -578,21 +579,6 @@ extern long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
unsigned int cmd, unsigned long arg);

/* functions for preparation of BKL removal */
-
-/*
- * tty_lock_nested get the tty_lock while potentially holding it
- *
- * The Big TTY Mutex is a recursive lock, meaning you can take it
- * from a thread that is already holding it.
- * This is bad for a number of reasons, so tty_lock_nested should
- * really be used as rarely as possible. If a code location can
- * be shown to never get called with this held already, it should
- * use tty_lock() instead.
- */
-static inline void __lockfunc tty_lock_nested(void) __acquires(kernel_lock)
-{
- lock_kernel();
-}
static inline void tty_lock(void) __acquires(kernel_lock)
{
#ifdef CONFIG_LOCK_KERNEL
--
1.7.2

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Prev: [PATCH 27/68] vc: Locking clean up
Next: [PATCH 48/68] serial: max3107: Abstract out the platform specific bits