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Date: Tue, 19 Jul 2022 05:50:16 -1000 From: Tejun Heo <tj@...nel.org> To: Jinke Han <hanjinke.666@...edance.com> Cc: axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org Subject: Re: [PATCH v2] block: don't allow the same type rq_qos add more than once On Tue, Jul 19, 2022 at 03:02:58PM +0800, Jinke Han wrote: > From: Jinke Han <hanjinke.666@...edance.com> > > In our test of iocost, we encounttered some list add/del corrutions of > inner_walk list in ioc_timer_fn. > > The reason can be descripted as follow: > cpu 0 cpu 1 > ioc_qos_write ioc_qos_write > > ioc = q_to_ioc(bdev_get_queue(bdev)); > if (!ioc) { > ioc = kzalloc(); ioc = q_to_ioc(bdev_get_queue(bdev)); > if (!ioc) { > ioc = kzalloc(); > ... > rq_qos_add(q, rqos); > } > ... > rq_qos_add(q, rqos); > ... > } > > When the io.cost.qos file is written by two cpu concurrently, rq_qos may > be added to one disk twice. In that case, there will be two iocs enabled > and running on one disk. They own different iocgs on their active list. > In the ioc_timer_fn function, because of the iocgs from two ioc have the > same root iocg, the root iocg's walk_list may be overwritten by each > other and this lead to list add/del corrutions in building or destorying > the inner_walk list. > > And so far, the blk-rq-qos framework works in case that one instance for > one type rq_qos per queue by default. This patch make this explicit and > also fix the crash above. > > Signed-off-by: Jinke Han <hanjinke.666@...edance.com> Acked-by: Tejun Heo <tj@...nel.org> Thanks. -- tejun
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