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From: Roland McGrath <roland@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
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Cc: Christoph Hellwig <hch@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 4/12 v2] ptrace: introduce the empty "struct
	ptrace_context"
In-Reply-To: Oleg Nesterov's message of  Thursday, 28 May 2009 13:35:45 +0200 <20090528113545.GA18691@redhat.com>
References: <20090528113545.GA18691@redhat.com>
X-Windows: the problem for your problem.
Message-Id: <20090528211540.2A5BAFC2BD@magilla.sf.frob.com>
Date: Thu, 28 May 2009 14:15:40 -0700 (PDT)
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> +	task_lock(tsk);
> +	if (likely(!tsk->ptrace_ctx))
> +		tsk->ptrace_ctx = ptrace_ctx;
> +	else
> +		kfree(ptrace_ctx);
> +	task_unlock(tsk);

I don't think it's kosher call kfree with task_lock() held.
The kfree case is a very unlikely path, so it can be:

	task_lock(tsk);
	if (likely(!tsk->ptrace_ctx)) {
		tsk->ptrace_ctx = ptrace_ctx;
		task_unlock(tsk);
		return 0;
	}

	task_unlock(tsk);
	kfree(ptrace_ctx);

Thanks,
Roland