From: Ming Lei <ming.lei@redhat.com>
To: John Garry <john.garry@huawei.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, hch@lst.de, hare@suse.de,
ppvk@codeaurora.org, bvanassche@acm.org,
kashyap.desai@broadcom.com
Subject: Re: [RFC PATCH] blk-mq: Clean up references when freeing rqs
Date: Thu, 10 Dec 2020 10:07:45 +0800 [thread overview]
Message-ID: <20201210020745.GA1363446@T590> (raw)
In-Reply-To: <13327a68-6f86-96da-0c5f-5fa0be326d6f@huawei.com>
On Wed, Dec 09, 2020 at 09:55:30AM +0000, John Garry wrote:
> On 09/12/2020 01:01, Ming Lei wrote:
> > blk_mq_queue_tag_busy_iter() can be run on another request queue just
> > between one driver tag is allocated and updating the request map, so one
> > extra request reference still can be grabbed.
> >
> > So looks only holding one queue's usage_counter doesn't help this issue, since
> > bt_for_each() always iterates on driver tags wide.
> >
> > > But I didn't see such a guard for blk_mq_tagset_busy_iter().
> > IMO there isn't real difference between the two iteration.
>
> ok, I see. Let me try to recreate that one, which will prob again require
> artificial delays added.
>
> Apart from this, my concern is that we come with for a solution, but it's a
> complicated solution and may not be accepted as this issue is not seen as a
> problem in practice.
If that is the case, I'd suggest to consider the solution in the
following link:
https://lore.kernel.org/linux-block/20200820180335.3109216-1-ming.lei@redhat.com/
At least, the idea is simple, which can be extended to support allocate driver tags
request pool dynamically.
Thanks,
Ming
next prev parent reply other threads:[~2020-12-10 2:09 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 13:02 [RFC PATCH] blk-mq: Clean up references when freeing rqs John Garry
2020-12-02 3:31 ` Ming Lei
2020-12-02 11:18 ` John Garry
2020-12-03 0:55 ` Ming Lei
2020-12-03 9:26 ` John Garry
2020-12-08 11:36 ` John Garry
2020-12-08 17:36 ` John Garry
2020-12-09 1:01 ` Ming Lei
2020-12-09 9:55 ` John Garry
2020-12-10 2:07 ` Ming Lei [this message]
2020-12-10 10:44 ` John Garry
2020-12-10 12:22 ` John Garry
2020-12-11 0:21 ` Ming Lei
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