atomic/tty: Fix up atomic abuse in ldsem

Mark found ldsem_cmpxchg() needed an (atomic_long_t *) cast to keep
working after making the atomic_long interface type safe.

Needing casts is bad form, which made me look at the code. There are no
ld_semaphore::count users outside of these functions so there is no
reason why it can not be an atomic_long_t in the first place, obviating
the need for this cast.

That also ensures the loads use atomic_long_read(), which implies (at
least) READ_ONCE() in order to guarantee single-copy-atomic loads.

When using atomic_long_try_cmpxchg() the ldsem_cmpxchg() wrapper gets
very thin (the only difference is not changing *old on success, which
most callers don't seem to care about).

So rework the whole thing to use atomic_long_t and its accessors
directly.

While there, fixup all the horrible comment styles.

Cc: Peter Hurley <peter@hurleysoftware.com>
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index 1ef64d4ad887..840894ca3fc0 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -119,13 +119,13 @@
 
 #include <linux/fs.h>
 #include <linux/wait.h>
-
+#include <linux/atomic.h>
 
 /*
  * the semaphore definition
  */
 struct ld_semaphore {
-	long			count;
+	atomic_long_t		count;
 	raw_spinlock_t		wait_lock;
 	unsigned int		wait_readers;
 	struct list_head	read_wait;