2012-06-30 09:39:58

by Jeff Liu

Subject: [PATCH 1/2] Add a new helper for sleepable BTM acquirements which is used by tty_write_message()

This helper only used by tty_write_message(), it will sleep until BTM lock acquired.

Signed-off-by: Jie Liu <[email protected]>
---
drivers/tty/tty_mutex.c | 13 +++++++++++++
include/linux/tty.h | 1 +
2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 9ff986c..e638636 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -30,3 +30,16 @@ void __lockfunc tty_unlock(void)
mutex_unlock(&big_tty_mutex);
}
EXPORT_SYMBOL(tty_unlock);
+
+/*
+ * Wait until getting the big tty mutex.
+ * This function only used by tty_write_message().
+ */
+void __lockfunc tty_lock_wait(void)
+{
+ while (!mutex_trylock(&big_tty_mutex)) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ schedule();
+ }
+}
+EXPORT_SYMBOL(tty_lock_wait);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 9f47ab5..5e01e0b 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -607,6 +607,7 @@ extern long vt_compat_ioctl(struct tty_struct *tty,
/* functions for preparation of BKL removal */
extern void __lockfunc tty_lock(void) __acquires(tty_lock);
extern void __lockfunc tty_unlock(void) __releases(tty_lock);
+extern void __lockfunc tty_lock_wait(void) __acquires(tty_lock);

/*
* this shall be called only from where BTM is held (like close)
--
1.7.9

2012-06-30 12:31:57

by Alan

Subject: Re: [PATCH 1/2] Add a new helper for sleepable BTM acquirements which is used by tty_write_message()

On Sat, 30 Jun 2012 17:39:58 +0800
Jeff Liu <[email protected]> wrote:

> This helper only used by tty_write_message(), it will sleep until BTM lock acquired.

This makes no sense at all. mutexes already sleep. Your code is also
wrong for real time processes.

So NAK.