linux-kernel - Re: [PATCH] rcu/nocb: Fix possible invalid rdp's->nocb_cb

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Message-ID: <aG0jDkBqPGm9-Wia@localhost.localdomain>
Date: Tue, 8 Jul 2025 15:54:22 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Zqiang <qiang.zhang1211@...il.com>
Cc: paulmck@...nel.org, neeraj.upadhyay@...nel.org, joel@...lfernandes.org,
	urezki@...il.com, boqun.feng@...il.com, rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread
 pointer access

Le Wed, May 07, 2025 at 07:26:05PM +0800, Zqiang a écrit :
> In the preparation stage of CPU online, if the corresponding
> the rdp's->nocb_cb_kthread does not exist, will be created,
> there is a situation where the rdp's rcuop kthreads creation fails,
> and then de-offload this CPU's rdp, does not assign this CPU's
> rdp->nocb_cb_kthread pointer, but this rdp's->nocb_gp_rdp and
> rdp's->rdp_gp->nocb_gp_kthread is still valid.
> 
> This will cause the subsequent re-offload operation of this offline
> CPU, which will pass the conditional check and the kthread_unpark()
> will access invalid rdp's->nocb_cb_kthread pointer.
> 
> This commit therefore use rdp's->nocb_gp_kthread instead of
> rdp_gp's->nocb_gp_kthread for safety check.
> 
> Signed-off-by: Zqiang <qiang.zhang1211@...il.com>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>

-- 
Frederic Weisbecker
SUSE Labs