linux-kernel - [PATCH v3 06/14] ipc: Remove redundant rcu_read_lock/unlock() in spin

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Message-Id: <20250916044735.2316171-7-dolinux.peng@gmail.com>
Date: Tue, 16 Sep 2025 12:47:27 +0800
From: pengdonglin <dolinux.peng@...il.com>
To: tj@...nel.org,
	tony.luck@...el.com,
	jani.nikula@...ux.intel.com,
	ap420073@...il.com,
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Cc: bigeasy@...utronix.de,
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	pengdonglin <dolinux.peng@...il.com>,
	pengdonglin <pengdonglin@...omi.com>
Subject: [PATCH v3 06/14] ipc: Remove redundant rcu_read_lock/unlock() in spin_lock

From: pengdonglin <pengdonglin@...omi.com>

Since commit a8bb74acd8efe ("rcu: Consolidate RCU-sched update-side function definitions")
there is no difference between rcu_read_lock(), rcu_read_lock_bh() and
rcu_read_lock_sched() in terms of RCU read section and the relevant grace
period. That means that spin_lock(), which implies rcu_read_lock_sched(),
also implies rcu_read_lock().

There is no need no explicitly start a RCU read section if one has already
been started implicitly by spin_lock().

Simplify the code and remove the inner rcu_read_lock() invocation.

Signed-off-by: pengdonglin <pengdonglin@...omi.com>
Signed-off-by: pengdonglin <dolinux.peng@...il.com>
---
 ipc/msg.c  | 1 -
 ipc/sem.c  | 1 -
 ipc/shm.c  | 1 -
 ipc/util.c | 2 --
 4 files changed, 5 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index ee6af4fe52bf..1e579b57023f 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -179,7 +179,6 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
 	}
 
 	ipc_unlock_object(&msq->q_perm);
-	rcu_read_unlock();
 
 	return msq->q_perm.id;
 }
diff --git a/ipc/sem.c b/ipc/sem.c
index a39cdc7bf88f..38ad57b2b558 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -579,7 +579,6 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
 	ns->used_sems += nsems;
 
 	sem_unlock(sma, -1);
-	rcu_read_unlock();
 
 	return sma->sem_perm.id;
 }
diff --git a/ipc/shm.c b/ipc/shm.c
index a9310b6dbbc3..61fae1b6a18e 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -795,7 +795,6 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
 	error = shp->shm_perm.id;
 
 	ipc_unlock_object(&shp->shm_perm);
-	rcu_read_unlock();
 	return error;
 
 no_id:
diff --git a/ipc/util.c b/ipc/util.c
index cae60f11d9c2..1be691b5dcad 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -293,7 +293,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
 	idr_preload(GFP_KERNEL);
 
 	spin_lock_init(&new->lock);
-	rcu_read_lock();
 	spin_lock(&new->lock);
 
 	current_euid_egid(&euid, &egid);
@@ -316,7 +315,6 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
 	if (idx < 0) {
 		new->deleted = true;
 		spin_unlock(&new->lock);
-		rcu_read_unlock();
 		return idx;
 	}
 
-- 
2.34.1