Re: [PATCH v2] nvme-tcp: Check if request has started before processing it

Hi Sagi,

On Fri, May 07, 2021 at 04:22:30PM -0700, Sagi Grimberg wrote:

Yea, maybe something like this?

I did give this a spin with blktests (loopback device) and on real
hardware (FC). Seems to do work fine. Just two things.

+/*
+ * nvme command_id is constructed as such:
+ * | xxxx | xxxxxxxxxxxx |
+ *   gen    request tag
+ */
+#define nvme_cid_install_genctr(gen)           ((gen & 0xf) << 12)
+#define nvme_genctr_from_cid(cid)              ((cid & 0xf000) >> 12)
+#define nvme_tag_from_cid(cid)                 (cid & 0xfff)
+
+static inline u16 nvme_cid(struct request *rq)
+{
+       return nvme_cid_install_genctr(nvme_req(rq)->genctr++) | rq->tag;
+}

-       return nvme_cid_install_genctr(nvme_req(rq)->genctr++) | rq->tag;
+       nvme_req(rq)->genctr = ++nvme_req(rq)->genctr & 0xf;
+       return nvme_cid_install_genctr(nvme_req(rq)->genctr) | rq->tag;

The first issue, it really needs prefix increment if you want to write
it in one line. And it should store only the first 4 bits.
nvme_find_rq() would complain with 0x0 != 0x10 after the first overflow.

+static inline struct request *nvme_find_rq(struct blk_mq_tags *tags,
+               u16 command_id)
+{
+       u8 genctr = nvme_genctr_from_cid(command_id);
+       u16 tag = nvme_tag_from_cid(command_id);
+       struct request *rq;
+
+       rq = blk_mq_tag_to_rq(tags, tag);
+       if (unlikely(!rq)) {
+               pr_err("could not locate request for tag %#x\n",
+                       tag);
+               return NULL;
+       }
+       if (unlikely(nvme_req(rq)->genctr != genctr)) {
+               dev_err(nvme_req(rq)->ctrl->device,
+                       "request %#x genctr mismatch (got %#x expected
%#x)\n",
+                       tag, nvme_req(rq)->genctr, genctr);

-                       tag, nvme_req(rq)->genctr, genctr);
+                       tag, genctr, nvme_req(rq)->genctr);

The arguments are in the wrong order. Got me a bit confused.

Are you going to send out a proper patch? I'd like to move things
forward and could offer to do some more testing if needed.

Thanks,
Daniel

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