From: Kashyap Desai <kashyap.desai@broadcom.com>
To: Bart Van Assche <bvanassche@acm.org>,
linux-block <linux-block@vger.kernel.org>,
Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>,
linux-scsi <linux-scsi@vger.kernel.org>
Cc: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>,
Sreekanth Reddy <sreekanth.reddy@broadcom.com>,
Sathya Prakash Veerichetty <sathya.prakash@broadcom.com>
Subject: RE: [PATCH] blk-mq: Set request mapping to NULL in blk_mq_put_driver_tag
Date: Tue, 4 Dec 2018 22:17:51 +0530 [thread overview]
Message-ID: <d56ddf2b485c13445fff5f9c36dd3c87@mail.gmail.com> (raw)
In-Reply-To: <7e8e1fe2-9f91-a370-a98c-43cdad1f6e8e@acm.org>
+ Linux-scsi
> > diff --git a/block/blk-mq.h b/block/blk-mq.h
> > index 9497b47..57432be 100644
> > --- a/block/blk-mq.h
> > +++ b/block/blk-mq.h
> > @@ -175,6 +175,7 @@ static inline bool
> > blk_mq_get_dispatch_budget(struct blk_mq_hw_ctx *hctx)
> > static inline void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx,
> > struct request *rq)
> > {
> > + hctx->tags->rqs[rq->tag] = NULL;
> > blk_mq_put_tag(hctx, hctx->tags, rq->mq_ctx, rq->tag);
> > rq->tag = -1;
>
> No SCSI driver should call scsi_host_find_tag() after a request has
> finished. The above patch introduces yet another race and hence can't be
> a proper fix.
Bart, many scsi drivers use scsi_host_find_tag() to traverse max tag_id to
find out pending IO in firmware.
One of the use case is - HBA firmware recovery. In case of firmware
recovery, driver may require to traverse the list and return back pending
scsi command to SML for retry.
I quickly grep the scsi code and found that snic_scsi, qla4xxx, fnic,
mpt3sas are using API scsi_host_find_tag for the same purpose.
Without this patch, we hit very basic kernel panic due to page fault. This
is not an issue in non-mq code path. Non-mq path use
blk_map_queue_find_tag() and that particular API does not provide stale
requests.
Kashyap
>
> Bart.
next prev parent reply other threads:[~2018-12-04 16:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-04 10:00 [PATCH] blk-mq: Set request mapping to NULL in blk_mq_put_driver_tag Kashyap Desai
2018-12-04 11:35 ` Ming Lei
2018-12-04 16:51 ` Kashyap Desai
2018-12-04 14:48 ` Bart Van Assche
2018-12-04 16:47 ` Kashyap Desai [this message]
2018-12-04 17:14 ` Bart Van Assche
2018-12-04 18:18 ` +AFs-PATCH+AF0- blk-mq: Set request mapping to NULL in blk+AF8-mq+AF8-put+AF8-driver+AF8-tag Kashyap Desai
2018-12-04 19:35 ` Bart Van Assche
2018-12-06 0:33 ` Ming Lei
2018-12-06 5:45 ` Kashyap Desai
2018-12-06 15:22 ` Jens Axboe
2018-12-07 7:16 ` Kashyap Desai
2018-12-07 10:20 ` Ming Lei
2018-12-07 10:34 ` Kashyap Desai
2018-12-11 15:06 ` Kashyap Desai
2018-12-14 6:22 ` Kashyap Desai
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