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

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Message-ID: <aUEqAIsrk47rHsuP@redhat.com>
Date: Tue, 16 Dec 2025 10:44:32 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Tycho Andersen <tycho@...nel.org>, Mateusz Guzik <mjguzik@...il.com>
Cc: Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pid: remove unnecessary idr_preload()

On 12/15, Tycho Andersen wrote:
>
> 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().

Yes. The extra idr_preload() was needed for pidfs_add_pid() after the commit
9698d5a483654 ("pidfs: rework inode number allocation").

But please see
[PATCH v3 2/2] pid: only take pidmap_lock once on alloc
https://lore.kernel.org/all/20251206131955.780557-3-mjguzik@gmail.com/

This patch removes the unnecessary idr_preload() too.

Oleg.