Revert "nvme-pci: remove last_sq_tail"

Multiple CPUs may be mapped to the same hctx, allowing mulitple
submission contexts to attempt commit_rqs(). We need to verify we're
not writing the same doorbell value multiple times since that's a spec
violation.

Revert commit 54b2fcee1db041a83b52b51752dade6090cf952f.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1878596
Reported-by: "B.L. Jones" <brandon.gustav@googlemail.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index df8f3612107f1d0ffbe6671f971af3d615fa6bdc..0578ff253c4775a54c02297b7c99f0c588c7cd6c 100644 (file)
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -198,6 +198,7 @@ struct nvme_queue {
        u32 q_depth;
        u16 cq_vector;
        u16 sq_tail;
+       u16 last_sq_tail;
        u16 cq_head;
        u16 qid;
        u8 cq_phase;
@@ -455,11 +456,24 @@ static int nvme_pci_map_queues(struct blk_mq_tag_set *set)
        return 0;
 }
 
-static inline void nvme_write_sq_db(struct nvme_queue *nvmeq)
+/*
+ * Write sq tail if we are asked to, or if the next command would wrap.
+ */
+static inline void nvme_write_sq_db(struct nvme_queue *nvmeq, bool write_sq)
 {
+       if (!write_sq) {
+               u16 next_tail = nvmeq->sq_tail + 1;
+
+               if (next_tail == nvmeq->q_depth)
+                       next_tail = 0;
+               if (next_tail != nvmeq->last_sq_tail)
+                       return;
+       }
+
        if (nvme_dbbuf_update_and_check_event(nvmeq->sq_tail,
                        nvmeq->dbbuf_sq_db, nvmeq->dbbuf_sq_ei))
                writel(nvmeq->sq_tail, nvmeq->q_db);
+       nvmeq->last_sq_tail = nvmeq->sq_tail;
 }
 
 /**
@@ -476,8 +490,7 @@ static void nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd,
               cmd, sizeof(*cmd));
        if (++nvmeq->sq_tail == nvmeq->q_depth)
                nvmeq->sq_tail = 0;
-       if (write_sq)
-               nvme_write_sq_db(nvmeq);
+       nvme_write_sq_db(nvmeq, write_sq);
        spin_unlock(&nvmeq->sq_lock);
 }
 
@@ -486,7 +499,8 @@ static void nvme_commit_rqs(struct blk_mq_hw_ctx *hctx)
        struct nvme_queue *nvmeq = hctx->driver_data;
 
        spin_lock(&nvmeq->sq_lock);
-       nvme_write_sq_db(nvmeq);
+       if (nvmeq->sq_tail != nvmeq->last_sq_tail)
+               nvme_write_sq_db(nvmeq, true);
        spin_unlock(&nvmeq->sq_lock);
 }
 
@@ -1496,6 +1510,7 @@ static void nvme_init_queue(struct nvme_queue *nvmeq, u16 qid)
        struct nvme_dev *dev = nvmeq->dev;
 
        nvmeq->sq_tail = 0;
+       nvmeq->last_sq_tail = 0;
        nvmeq->cq_head = 0;
        nvmeq->cq_phase = 1;
        nvmeq->q_db = &dev->dbs[qid * 2 * dev->db_stride];