Re: [PATCH 3/4] blk-mq: remove a pointless queue enter pair in blk_mq_alloc_request_hctx

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To: Bart Van Assche <bvanassche@xxxxxxx>
Subject: Re: [PATCH 3/4] blk-mq: remove a pointless queue enter pair in blk_mq_alloc_request_hctx
From: Christoph Hellwig <hch@xxxxxx>
Date: Sat, 16 May 2020 19:31:50 +0200
Cc: Christoph Hellwig <hch@xxxxxx>, axboe@xxxxxxxxx, linux-block@xxxxxxxxxxxxxxx
In-reply-to: <87513e5c-270c-41cf-51d8-9106351449b5@acm.org>
References: <20200516153430.294324-1-hch@lst.de> <20200516153430.294324-4-hch@lst.de> <87513e5c-270c-41cf-51d8-9106351449b5@acm.org>
User-agent: Mutt/1.5.17 (2007-11-01)

On Sat, May 16, 2020 at 09:28:22AM -0700, Bart Van Assche wrote:
> This change looks wrong to me. blk_mq_update_nr_hw_queues() modifies
> q->queue_hw_ctx so q_usage_counter must be incremented before that
> pointer is dereferenced.

True, I'll drop that part.

References:
- avoid a few q_usage_counter roundtrips v2
  - From: Christoph Hellwig
- [PATCH 3/4] blk-mq: remove a pointless queue enter pair in blk_mq_alloc_request_hctx
  - From: Christoph Hellwig
- Re: [PATCH 3/4] blk-mq: remove a pointless queue enter pair in blk_mq_alloc_request_hctx
  - From: Bart Van Assche

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