[PATCH] [v2]net:ppp: remove disc_data_lock in ppp line discipline

[Gao Yan]

In tty layer, it provides tty->ldisc_sem to protect all tty_ldisc_ops
including ppp_sync_ldisc. So I think tty->ldisc_sem can also
protect tty->disc_data, and the disc_data_lock is not necessary.

Signed-off-by: Gao Yan 
---
 drivers/net/ppp/ppp_async.c   | 11 ++-
 drivers/net/ppp/ppp_synctty.c | 12 ++--
 2 files changed, 4 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
index 29a0917a8..20b50facd 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 0f338752c..53fb68e29 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -129,17 +129,12 @@ 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 +208,9 @@ 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

[PATCH] net: remove disc_data_lock in ppp line discipline

[Gao Yan]

In tty layer, it use tty->ldisc_sem 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 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 
---
 drivers/net/ppp/ppp_async.c   | 11 ++-
 drivers/net/ppp/ppp_synctty.c | 12 ++--
 2 files changed, 4 insertions(+), 19 deletions(-)

diff --git a/drivers/net/ppp/ppp_async.c b/drivers/net/ppp/ppp_async.c
index 29a0917a8..20b50facd 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 0f338752c..53fb68e29 100644
--- a/drivers/net/ppp/ppp_synctty.c
+++ b/drivers/net/ppp/ppp_synctty.c
@@ -129,17 +129,12 @@ 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 +208,9 @@ 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

[PATCH] net: remove disc_data_lock in ppp line discipline

[Gao Yan]

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 
---
 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