linux-kernel - Re: [GIT PULL] Revert of the IO stat fix

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Message-ID: <4CF52DDE.4070407@redhat.com>
Date:	Tue, 30 Nov 2010 18:01:18 +0100
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Jens Axboe <jaxboe@...ionio.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [GIT PULL] Revert of the IO stat fix

On 10/24/2010 10:44 PM, Jens Axboe wrote:
> diff --git a/block/genhd.c b/block/genhd.c
> index a8adf96..7d4d860 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -930,14 +930,9 @@ static void disk_free_ptbl_rcu_cb(struct rcu_head *head)
>  	struct disk_part_tbl *ptbl =
>  		container_of(head, struct disk_part_tbl, rcu_head);
>  	struct gendisk *disk = ptbl->disk;
> -	struct request_queue *q = disk->queue;
> -	unsigned long flags;
>  
>  	kfree(ptbl);
> -
> -	spin_lock_irqsave(q->queue_lock, flags);
> -	elv_quiesce_end(q);
> -	spin_unlock_irqrestore(q->queue_lock, flags);
> +	elv_quiesce_end(disk->queue);

Here, the queue may be already gone. We should check it is still here and alive:

static void disk_free_ptbl_rcu_cb(struct rcu_head *head)
{
	struct disk_part_tbl *ptbl =
		container_of(head, struct disk_part_tbl, rcu_head);
	struct gendisk *disk = ptbl->disk;
	struct request_queue *q = disk->queue;

	kfree(ptbl);
	if (q && !test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))
		elv_quiesce_end(q);
}


>  }
>  
>  /**
> @@ -962,10 +957,7 @@ static void disk_replace_part_tbl(struct gendisk *disk,
>  	if (old_ptbl) {
>  		rcu_assign_pointer(old_ptbl->last_lookup, NULL);
>  
> -		spin_lock_irq(q->queue_lock);
>  		elv_quiesce_start(q);

Same as above.

I'm not sure that is enough, but on my test machine these changes fix the crash
at USB key device removal.

Regards,
Jerome

> -		spin_unlock_irq(q->queue_lock);
> -
>  		call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
>  	}
>  }
--
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