linux-kernel - Re: [RFC][PATCH 3/3] Do not use rqhash when merges disabled

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Message-ID: <480FD648.70404@gelato.unsw.edu.au>
Date:	Thu, 24 Apr 2008 10:37:28 +1000
From:	Aaron Carroll <aaronc@...ato.unsw.edu.au>
To:	"Alan D. Brunelle" <Alan.Brunelle@...com>
CC:	linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC][PATCH 3/3] Do not use rqhash when merges disabled

Hi Alan,

Alan D. Brunelle wrote:
> --- a/block/elevator.c
> +++ b/block/elevator.c
> @@ -313,7 +313,7 @@ static inline void __elv_rqhash_del(struct request *rq)
>  
>  static void elv_rqhash_del(struct request_queue *q, struct request *rq)
>  {
> -	if (ELV_ON_HASH(rq))
> +	if (!blk_queue_nomerges(q) && ELV_ON_HASH(rq))
>  		__elv_rqhash_del(rq);
>  }

If you switch the nomerges tunable while requests are in flight, it is possible that
a request is put into the rqhash table but not removed here, leading to the BUG_ON
in elv_dequeue_request() triggering.  ELV_ON_HASH needs to be checked regardless of
the nomerges state.

 -- Aaron

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