[PATCH net-next] ppp: convert chan_sem to a mutex

[PATCH net-next] ppp: convert chan_sem to a mutex

[Qingfang Deng]

chan_sem's read-side lock is taken under another mutex, so there is no
benefit in keeping it as an rwsem. Replace the rwsem with a mutex.

Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
---
 drivers/net/ppp/ppp_generic.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index cacc4c3a37d2..08bb89765487 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -39,7 +39,6 @@
 #include <linux/ip.h>
 #include <linux/tcp.h>
 #include <linux/spinlock.h>
-#include <linux/rwsem.h>
 #include <linux/stddef.h>
 #include <linux/device.h>
 #include <linux/mutex.h>
@@ -176,7 +175,7 @@ struct channel {
 	struct ppp_file	file;		/* stuff for read/write/poll */
 	struct list_head list;		/* link in all/new_channels list */
 	struct ppp_channel *chan;	/* public channel data structure */
-	struct rw_semaphore chan_sem;	/* protects `chan' during chan ioctl */
+	struct mutex chan_sem;		/* protects `chan' during chan ioctl */
 	spinlock_t	downl;		/* protects `chan', file.xq dequeue */
 	struct ppp __rcu *ppp;		/* ppp unit we're connected to */
 	struct net	*chan_net;	/* the net channel belongs to */
@@ -788,12 +787,12 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			break;
 
 		default:
-			down_read(&pch->chan_sem);
+			mutex_lock(&pch->chan_sem);
 			chan = pch->chan;
 			err = -ENOTTY;
 			if (chan && chan->ops->ioctl)
 				err = chan->ops->ioctl(chan, cmd, arg);
-			up_read(&pch->chan_sem);
+			mutex_unlock(&pch->chan_sem);
 		}
 		goto out;
 	}
@@ -2922,7 +2921,7 @@ int ppp_register_net_channel(struct net *net, struct ppp_channel *chan)
 #ifdef CONFIG_PPP_MULTILINK
 	pch->lastseq = -1;
 #endif /* CONFIG_PPP_MULTILINK */
-	init_rwsem(&pch->chan_sem);
+	mutex_init(&pch->chan_sem);
 	spin_lock_init(&pch->downl);
 	spin_lock_init(&pch->upl);
 
@@ -3005,11 +3004,11 @@ ppp_unregister_channel(struct ppp_channel *chan)
 	 * the channel's start_xmit or ioctl routine before we proceed.
 	 */
 	ppp_disconnect_channel(pch);
-	down_write(&pch->chan_sem);
+	mutex_lock(&pch->chan_sem);
 	spin_lock_bh(&pch->downl);
 	pch->chan = NULL;
 	spin_unlock_bh(&pch->downl);
-	up_write(&pch->chan_sem);
+	mutex_unlock(&pch->chan_sem);
 
 	pn = ppp_pernet(pch->chan_net);
 	spin_lock_bh(&pn->all_channels_lock);
@@ -3600,6 +3599,7 @@ static void ppp_release_channel(struct channel *pch)
 		pr_err("ppp: destroying undead channel %p !\n", pch);
 		return;
 	}
+	mutex_destroy(&pch->chan_sem);
 	call_rcu(&pch->rcu, ppp_release_channel_free);
 }
 
-- 
2.43.0

Re: [PATCH net-next] ppp: convert chan_sem to a mutex

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 27 Jul 2026 11:28:00 +0800 you wrote:
> chan_sem's read-side lock is taken under another mutex, so there is no
> benefit in keeping it as an rwsem. Replace the rwsem with a mutex.
> 
> Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
> ---
>  drivers/net/ppp/ppp_generic.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)

Here is the summary with links:
  - [net-next] ppp: convert chan_sem to a mutex
    https://git.kernel.org/netdev/net-next/c/2bb54b49e9d5

You are awesome, thank you!
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