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Date: Wed, 25 Mar 2026 16:38:26 +0100
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>, linux-rt-devel@lists.linux.dev,
	Clark Williams <clrkwllms@kernel.org>, linux-kernel@vger.kernel.org,
	"Paul E. McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH v1] irq_work: Fix use-after-free in irq_work_single on
 PREEMPT_RT
Message-ID: <20260325153826.EbSqlX_n@linutronix.de>
References: <20260325030508.321405-1-jiayuan.chen@linux.dev>
 <20260325111351.1d38a0bc@gandalf.local.home>
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In-Reply-To: <20260325111351.1d38a0bc@gandalf.local.home>

On 2026-03-25 11:13:51 [-0400], Steven Rostedt wrote:
> Yeah, this is open coding the rcuwait_wake_up().
> 
> I'm not sure we want to do this.
> 
> Perhaps RCU could provide a way to save the rcuwait?
> 
> 	struct rcuwait = __RCUWAIT_INITIALIZER(rcuwait);
> 
> 	[..]
> 
> 		rcuwait_copy(&rcuwait, &work->irqwait);
> 
> 	[..]
> 
> 		rcuwait_wake_up(&rcuwait);
> 
> ?

Most irq-work aren't free()ed since they are static and remain around.
There is no task assigned if there is no active waiter.
Wouldn't it be easier to kfree_rcu() the struct using the irq-work?

> > +		put_task_struct(waiter);
> > +	}
> 
> -- Steve

Sebastian