From: "Dr. David Alan Gilbert" <linux@treblig.org>

ldsem_down_write_trylock() was added in 2013 by
commit 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore")
but hasn't been used.

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
---
 drivers/tty/tty_ldsem.c   | 17 -----------------
 include/linux/tty_ldisc.h |  1 -
 2 files changed, 18 deletions(-)

diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c
index 3be428c16260..4e18031a5ca3 100644
--- a/drivers/tty/tty_ldsem.c
+++ b/drivers/tty/tty_ldsem.c
@@ -366,23 +366,6 @@ int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
 	return __ldsem_down_write_nested(sem, 0, timeout);
 }
 
-/*
- * trylock for writing -- returns 1 if successful, 0 if contention
- */
-int ldsem_down_write_trylock(struct ld_semaphore *sem)
-{
-	long count = atomic_long_read(&sem->count);
-
-	while ((count & LDSEM_ACTIVE_MASK) == 0) {
-		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
-			rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
-			lock_acquired(&sem->dep_map, _RET_IP_);
-			return 1;
-		}
-	}
-	return 0;
-}
-
 /*
  * release a read lock
  */
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index af01e89074b2..c5cccc3fc1e8 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -39,7 +39,6 @@ do {								\
 int ldsem_down_read(struct ld_semaphore *sem, long timeout);
 int ldsem_down_read_trylock(struct ld_semaphore *sem);
 int ldsem_down_write(struct ld_semaphore *sem, long timeout);
-int ldsem_down_write_trylock(struct ld_semaphore *sem);
 void ldsem_up_read(struct ld_semaphore *sem);
 void ldsem_up_write(struct ld_semaphore *sem);
 
-- 
2.48.1

On 22. 01. 25, 2:25, linux@treblig.org wrote:
> From: "Dr. David Alan Gilbert" <linux@treblig.org>
> 
> ldsem_down_write_trylock() was added in 2013 by
> commit 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore")
> but hasn't been used.
> 
> Remove it.

Right, it was likely added for symmetry. However having untested+unused 
code is indeed wrong.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>

thanks,
-- 
js
suse labs