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

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Message-ID: <480FDB72.4030005@hp.com>
Date:	Wed, 23 Apr 2008 20:59:30 -0400
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	Aaron Carroll <aaronc@...ato.unsw.edu.au>
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

Aaron Carroll wrote:
> 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
> 
> 

Hi Aaron -

Good catch - that was a last minute addition, the ELV_ON_HASH should be
sufficient without the check for blk_queue_nomerges, right?

Alan
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