linux-kernel - [PATCH] pid: remove unnecessary idr

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Message-ID: <20251215201514.1343231-1-tycho@kernel.org>
Date: Mon, 15 Dec 2025 13:15:14 -0700
From: Tycho Andersen <tycho@...nel.org>
To: Christian Brauner <brauner@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>
Cc: linux-kernel@...r.kernel.org,
	"Tycho Andersen (AMD)" <tycho@...nel.org>
Subject: [PATCH] pid: remove unnecessary idr_preload()

From: "Tycho Andersen (AMD)" <tycho@...nel.org>

As near as I can tell, nothing in the second pidmap_lock critical section
actually allocates an id, so there is no need to do idr_preload().
idr_replace() does not, nor does pidfs_add_pid().

I boot tested this and built a kernel on a $large core system, so hopefully
that would have caught any errors.

Signed-off-by: Tycho Andersen (AMD) <tycho@...nel.org>
---
 kernel/pid.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/pid.c b/kernel/pid.c
index a31771bc89c1..b0fefeb0a1ec 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -270,7 +270,6 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 	INIT_HLIST_HEAD(&pid->inodes);
 
 	upid = pid->numbers + ns->level;
-	idr_preload(GFP_KERNEL);
 	spin_lock(&pidmap_lock);
 	if (!(ns->pid_allocated & PIDNS_ADDING))
 		goto out_unlock;
@@ -281,14 +280,12 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 		upid->ns->pid_allocated++;
 	}
 	spin_unlock(&pidmap_lock);
-	idr_preload_end();
 	ns_ref_active_get(ns);
 
 	return pid;
 
 out_unlock:
 	spin_unlock(&pidmap_lock);
-	idr_preload_end();
 	put_pid_ns(ns);
 
 out_free:

base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
-- 
2.52.0