* [PATCH] net: remove unnecessary disc_data_lock in ppp line discipline
@ 2021-05-21 7:57 Gao Yan
2021-05-21 8:33 ` Greg KH
0 siblings, 1 reply; 2+ messages in thread
From: Gao Yan @ 2021-05-21 7:57 UTC (permalink / raw)
To: gregkh, jirislaby, paulus, davem, kuba, linux-kernel; +Cc: Gao Yan
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@h3c.com>
---
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] net: remove unnecessary disc_data_lock in ppp line discipline
2021-05-21 7:57 [PATCH] net: remove unnecessary disc_data_lock in ppp line discipline Gao Yan
@ 2021-05-21 8:33 ` Greg KH
0 siblings, 0 replies; 2+ messages in thread
From: Greg KH @ 2021-05-21 8:33 UTC (permalink / raw)
To: Gao Yan; +Cc: jirislaby, paulus, davem, kuba, linux-kernel
On Fri, May 21, 2021 at 03:57:26PM +0800, Gao Yan wrote:
> 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@h3c.com>
> ---
> 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
>
So removing this lock is ok?
How did you test this? Is there anything wrong with keeping the
existing lock? Does it show up in a real-world workload as being a
problem? Unconstested locks should be almost a no-op.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 2+ messages in thread
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2021-05-21 7:57 [PATCH] net: remove unnecessary disc_data_lock in ppp line discipline Gao Yan
2021-05-21 8:33 ` Greg KH
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