linux-kernel - Re: [PATCH] random: fix possible sleeping allocation from irq context

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Message-ID: <20180425060017.GB3412@thunk.org>
Date:   Wed, 25 Apr 2018 02:00:17 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] random: fix possible sleeping allocation from irq context

On Wed, Apr 25, 2018 at 09:46:42AM +0900, Tetsuo Handa wrote:
> Theodore Ts\'o wrote:
> > We can do a sleeping allocation from an irq context when CONFIG_NUMA
> > is enabled.  Fix this by initializing the NUMA crng instances in a
> > workqueue.
> 
> Offloading to workqueue context itself would be OK,
> but this patch makes linux.git unbootable because
> 
> 	if (crng == &primary_crng && crng_init < 2) {
> 		invalidate_batched_entropy();
> 		numa_crng_init(); // <= Deferred to workqueue context.
> 		crng_init = 2; // <= Not waiting for workqueue context, and oops before console becomes ready. ;-)
> 		process_random_ready_list();
> 		wake_up_interruptible(&crng_init_wait);
> 		pr_notice(\"random: crng init done\\n\");
> 	}
> 
> Please don\'t pretend rng_ready() before workqueue context is processed.

Where's the oops?  It's not oopsing for me, and if the NUMA crng is
not initailized, the code in extract_entropy returns falls back to
using the primary_crng:

static void extract_crng(__u32 out[CHACHA20_BLOCK_WORDS])
{
	struct crng_state *crng = NULL;

#ifdef CONFIG_NUMA
	if (crng_node_pool)
		crng = crng_node_pool[numa_node_id()];
	if (crng == NULL)
#endif
		crng = &primary_crng;
	_extract_crng(crng, out);
}

						- Ted