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Message-ID: <e17f86f0-98ca-5c79-0d9b-43c628b72413@oracle.com>
Date: Mon, 18 Mar 2019 09:49:33 +0800
From: "jianchao.wang" <jianchao.w.wang@...cle.com>
To: Keith Busch <kbusch@...nel.org>
Cc: "axboe@...nel.dk" <axboe@...nel.dk>,
"linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
"jsmart2021@...il.com" <jsmart2021@...il.com>,
"bvanassche@....org" <bvanassche@....org>,
"josef@...icpanda.com" <josef@...icpanda.com>,
"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Busch, Keith" <keith.busch@...el.com>,
"hare@...e.de" <hare@...e.de>,
"jthumshirn@...e.de" <jthumshirn@...e.de>,
"hch@....de" <hch@....de>, "sagi@...mberg.me" <sagi@...mberg.me>
Subject: Re: [PATCH 2/8] blk-mq: change the method of iterating busy tags of a
request_queue
Hi Keith
On 3/16/19 12:16 AM, Keith Busch wrote:
> There is still a window where the check may succeed, but the request is
> being assigned to a completely different request_queue. The callback
> then operates on a request it doesn't own.
>
> Tag iteration from a driver can be safe only if the driver initiates a
> freeze and quiesced all queues sharing the same tagset first. The nvme
> driver does that, but I think there may need to be an additional grace
> period to wait for the allocation's queue_enter to call queue_exit to
> ensure the request is initialized through blk_mq_rq_ctx_init().
This patch is to avoid the use-after-free case in the comment.
The helper interface is used in following cases,
1. in flight request account
this case should not require so much accuracy
2. timeout check
a extra reference will be held there to avoid the request recycle
3. if it is used by driver, it should be enough that quiesce the request_queue
the driver usually wants to handle the in-flight ones, quiesce request_queue
could ensure all of tasks quit the hctx_lock and no one issue request any
more.
Thanks
Jianchao
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