linux-kernel - Re: [PATCH 2/2] dm: stay in blk_queue_bypass until queue becomes initialized

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Message-ID: <1351529115.24721.40.camel@twins>
Date:	Mon, 29 Oct 2012 17:45:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	device-mapper development <dm-devel@...hat.com>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Alasdair G Kergon <agk@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] dm: stay in blk_queue_bypass until queue becomes
 initialized

On Mon, 2012-10-29 at 12:38 -0400, Vivek Goyal wrote:
> Ok, so the question is what's wrong with calling synchronize_rcu() inside
> a mutex with CONFIG_PREEMPT=y. I don't know. Ccing paul mckenney  and
> peterz.

int blkcg_activate_policy(struct request_queue *q,

{

	...

        preloaded = !radix_tree_preload(GFP_KERNEL);

        blk_queue_bypass_start(q);




where:

int radix_tree_preload(gfp_t gfp_mask)
{
        struct radix_tree_preload *rtp;
        struct radix_tree_node *node;
        int ret = -ENOMEM;
        
        preempt_disable();


Seems obvious why it explodes..
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