Messages in this thread | | | Subject | Re: [PATCH v4 2/6] nbd: convert to use blk_mq_find_and_get_req() | From | "yukuai (C)" <> | Date | Wed, 8 Sep 2021 16:29:57 +0800 |
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On 2021/09/08 16:00, Ming Lei wrote: > On Wed, Sep 08, 2021 at 03:37:06PM +0800, yukuai (C) wrote: >> On 2021/09/08 15:30, Ming Lei wrote: >> >>>> +put_req: >>>> + if (req) >>>> + blk_mq_put_rq_ref(req); >>>> return ret ? ERR_PTR(ret) : cmd; >>> >>> After the request's refcnt is dropped, it can be freed immediately, then >>> one stale command is returned to caller. >> >> Hi, Ming >> >> It's right this patch leave this problem. Please take a look at patch 3 >> and patch 4, the problem should be fixed with these patches. > > Not see it is addressed in patch 3 & 4, and it is one obvious fault in > patch 2, please fix it from beginning by moving the refcnt drop > into recv_work().
Hi, Ming
With patch 3 & 4:
if nbd_read_stat() return a valid cmd, then the refcnt should not drop to 0 before blk_mq_complete_request() in recv_work().
if nbd_read_stat() failed, it won't be a problem if the request is freed immediately when refcnt is dropped in nbd_read_stat().
That's why I said that the problem will be fixed.
BTW, if we move the refcnt drop into recv_work, we can only do that if nbd_read_stat() return a valid cmd. If we get a valid rq and failed in the following checkings in nbd_read_stat(), it's better to drop the refcnt in nbd_read_stat().
> > BTW, the approach in patch 3 looks fine, which is very similar with > SCSI's handling.
Thanks for taking time reviewing these patches. Kuai > > Thanks, > Ming > > . >
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