[PATCH] net: remove disc_data_lock in ppp line discipline

From: Gao Yan
Date: Tue Dec 15 2020 - 10:13:52 EST


tty layer provide tty->ldisc_sem lock to protect tty->disc_data;
For examlpe, when cpu A is running ppp_synctty_ioctl that
hold the tty->ldisc_sem, so if cpu B calls ppp_synctty_close,
it will wait until cpu A release tty->ldisc_sem. So I think it is
unnecessary to have the 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 | 5 -----
drivers/net/ppp/ppp_synctty.c | 5 -----
2 files changed, 10 deletions(-)

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
index 29a0917a8..f8cb591d6 100644
--- a/drivers/net/ppp/ppp_async.c
+++ b/drivers/net/ppp/ppp_async.c
@@ -127,17 +127,14 @@ 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;

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

@@ -216,10 +213,8 @@ ppp_asynctty_close(struct tty_struct *tty)
{
struct asyncppp *ap;

- 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 0f338752c..8cdf7268c 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -129,17 +129,14 @@ 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;

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

@@ -215,10 +212,8 @@ ppp_sync_close(struct tty_struct *tty)
{
struct syncppp *ap;

- 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