From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: dm: fix imposition of queue_limits in dm_wq_work() thread Date: Mon, 28 Sep 2020 12:03:22 -0400 Message-ID: <20200928160322.GA23320@redhat.com> References: <20200927120435.44118-1-jefflexu@linux.alibaba.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200927120435.44118-1-jefflexu@linux.alibaba.com> To: Jeffle Xu Cc: dm-devel@redhat.com, joseph.qi@linux.alibaba.com, ming.lei@redhat.com, linux-block@vger.kernel.org List-Id: dm-devel.ids On Sun, Sep 27 2020 at 8:04am -0400, Jeffle Xu wrote: > Hi Mike, would you mind further expalin why bio processed by dm_wq_work() > always gets a previous ->submit_bio. Considering the following call graph: > > ->submit_bio, that is, dm_submit_bio > DMF_BLOCK_IO_FOR_SUSPEND set, thus queue_io() > > then worker thread dm_wq_work() > dm_process_bio // at this point. the input bio is the original bio > submitted to dm device > > Please let me know if I missed something. > > Thanks. > Jeffle In general you have a valid point, that blk_queue_split() won't have been done for the suspended device case, but blk_queue_split() cannot be used if not in ->submit_bio -- IIUC you cannot just do it from a worker thread and hope to have proper submission order (depth first) as provided by __submit_bio_noacct(). Because this IO will be submitted from worker you could have multiple threads allocating from the q->bio_split mempool at the same time. All said, I'm not quite sure how to address this report. But I'll keep at it and see what I can come up with. Thanks, Mike > Original commit log: > dm_process_bio() can be called by dm_wq_work(), and if the currently > processing bio is the very beginning bio submitted to the dm device, > that is it has not been handled by previous ->submit_bio, then we also > need to impose the queue_limits when it's in thread (dm_wq_work()). > > Fixes: cf9c37865557 ("dm: fix comment in dm_process_bio()") > Fixes: 568c73a355e0 ("dm: update dm_process_bio() to split bio if in ->make_request_fn()") > Signed-off-by: Jeffle Xu > --- > drivers/md/dm.c | 16 ++++++---------- > 1 file changed, 6 insertions(+), 10 deletions(-) > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > index 6ed05ca65a0f..54471c75ddef 100644 > --- a/drivers/md/dm.c > +++ b/drivers/md/dm.c > @@ -1744,17 +1744,13 @@ static blk_qc_t dm_process_bio(struct mapped_device *md, > } > > /* > - * If in ->submit_bio we need to use blk_queue_split(), otherwise > - * queue_limits for abnormal requests (e.g. discard, writesame, etc) > - * won't be imposed. > - * If called from dm_wq_work() for deferred bio processing, bio > - * was already handled by following code with previous ->submit_bio. > + * Call blk_queue_split() so that queue_limits for abnormal requests > + * (e.g. discard, writesame, etc) are ensured to be imposed, while > + * it's not needed for regular IO, since regular IO will be split by > + * following __split_and_process_bio. > */ > - if (current->bio_list) { > - if (is_abnormal_io(bio)) > - blk_queue_split(&bio); > - /* regular IO is split by __split_and_process_bio */ > - } > + if (is_abnormal_io(bio)) > + blk_queue_split(&bio); > > if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED) > return __process_bio(md, map, bio, ti); > -- > 2.27.0 >