tty: extract tty_flip_buffer_commit() from tty_flip_buffer_push()

stable inclusion
from stable-v5.10.134
commit a4bb7ef2d6f6d7158539f95b2fa97d658ea3cf75
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I5A5Y1
CVE: CVE-2022-1462

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a4bb7ef2d6f6d7158539f95b2fa97d658ea3cf75

--------------------------------

commit 716b1058 upstream.

We will need this new helper in the next patch.

Cc: Hillf Danton <hdanton@sina.com>
Cc: 一只狗 <chennbnbnb@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220707082558.9250-1-jslaby@suse.czSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYi Yang <yiyang13@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/tty/tty_buffer.c

@@ -524,6 +524,15 @@ static void flush_to_ldisc(struct work_struct *work)
 
 }
 
+static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
+{
+	/*
+	 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
+	 * buffer data.
+	 */
+	smp_store_release(&tail->commit, tail->used);
+}
+
 /**
  *	tty_flip_buffer_push	-	terminal
  *	@port: tty port to push
@@ -539,11 +548,7 @@ void tty_flip_buffer_push(struct tty_port *port)
 {
 	struct tty_bufhead *buf = &port->buf;
 
-	/*
-	 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
-	 * buffer data.
-	 */
-	smp_store_release(&buf->tail->commit, buf->tail->used);
+	tty_flip_buffer_commit(buf->tail);
 	queue_work(system_unbound_wq, &buf->work);
 }
 EXPORT_SYMBOL(tty_flip_buffer_push);