[PATCH] net: remove unnecessary disc_data_lock in ppp line discipline

From: Gao Yan
Date: Fri May 21 2021 - 05:22:17 EST


In tty layer, it use tty->ldisc_sem(using tty_ldisc_ref_wait and
tty_ldisc_deref) to proect tty_ldisc_ops.

So I think tty->ldisc_sem can also protect tty->disc_data;
For examlpe, When cpu A is running ppp_synctty_ioctl that hold
the tty->ldisc_sem, at the same time if cpu B calls ppp_synctty_close,
it will wait until cpu A release tty->ldisc_sem.

So I think it is unnecessary to define additional disc_data_lock;

cpu A cpu B
tty_ioctl tty_reopen
->hold tty->ldisc_sem ->hold tty->ldisc_sem(write), failed
->ld->ops->ioctl ->wait...
->release tty->ldisc_sem ->wait...OK,hold tty->ldisc_sem
->tty_ldisc_reinit
->tty_ldisc_close
->ld->ops->close

Signed-off-by: Gao Yan <gao.yanB@xxxxxxx>
---
drivers/net/ppp/ppp_async.c | 11 ++---------
drivers/net/ppp/ppp_synctty.c | 11 ++---------
2 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
index 8b41aa3fb..7bc4846f5 100644
--- a/drivers/net/ppp/ppp_async.c
+++ b/drivers/net/ppp/ppp_async.c
@@ -127,17 +127,13 @@ static const struct ppp_channel_ops async_ops = {
* FIXME: this is no longer true. The _close path for the ldisc is
* now guaranteed to be sane.
*/
-static DEFINE_RWLOCK(disc_data_lock);

static struct asyncppp *ap_get(struct tty_struct *tty)
{
- struct asyncppp *ap;
+ struct asyncppp *ap = tty->disc_data;

- read_lock(&disc_data_lock);
- ap = tty->disc_data;
if (ap != NULL)
refcount_inc(&ap->refcnt);
- read_unlock(&disc_data_lock);
return ap;
}

@@ -214,12 +210,9 @@ ppp_asynctty_open(struct tty_struct *tty)
static void
ppp_asynctty_close(struct tty_struct *tty)
{
- struct asyncppp *ap;
+ struct asyncppp *ap = tty->disc_data;

- write_lock_irq(&disc_data_lock);
- ap = tty->disc_data;
tty->disc_data = NULL;
- write_unlock_irq(&disc_data_lock);
if (!ap)
return;

diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c
index 576b6a93b..812f309c5 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -129,17 +129,13 @@ ppp_print_buffer (const char *name, const __u8 *buf, int count)
*
* FIXME: Fixed in tty_io nowadays.
*/
-static DEFINE_RWLOCK(disc_data_lock);

static struct syncppp *sp_get(struct tty_struct *tty)
{
- struct syncppp *ap;
+ struct syncppp *ap = tty->disc_data;

- read_lock(&disc_data_lock);
- ap = tty->disc_data;
if (ap != NULL)
refcount_inc(&ap->refcnt);
- read_unlock(&disc_data_lock);
return ap;
}

@@ -213,12 +209,9 @@ ppp_sync_open(struct tty_struct *tty)
static void
ppp_sync_close(struct tty_struct *tty)
{
- struct syncppp *ap;
+ struct syncppp *ap = tty->disc_data;

- write_lock_irq(&disc_data_lock);
- ap = tty->disc_data;
tty->disc_data = NULL;
- write_unlock_irq(&disc_data_lock);
if (!ap)
return;

--
2.17.1