Re: Kernel warning at drivers/infiniband/core/rw.c:349

On 10/12/21 17:30, Logan Gunthorpe wrote:

Best I can see from the code is that someone is passing an sg_cnt of
zero. Previously that would have returned -ENOMEM, but now it might be
ignored, in which case it would hit that WARNING and return -EIO.

That is not what is happening. The debug patch shown below learned me 
the following:
* The sg_cnt argument of rdma_rw_ctx_init() is not zero.
* After the rdma_rw_map_sgtable() call, sgt.nents is zero.

The debug patch that I used is as follows:

diff --git a/drivers/infiniband/core/rw.c b/drivers/infiniband/core/rw.c
index 5a3bd41b331c..a6dabea37958 100644
--- a/drivers/infiniband/core/rw.c
+++ b/drivers/infiniband/core/rw.c

@@ -326,11 +326,15 @@ int rdma_rw_ctx_init(struct rdma_rw_ctx *ctx, 

struct ib_qp *qp, u32 port_num,
  	};
  	int ret;

+	WARN_ON_ONCE(!sg_cnt);
+
  	ret = rdma_rw_map_sgtable(dev, &sgt, dir);
  	if (ret)
  		return ret;
  	sg_cnt = sgt.nents;

+	WARN_ON_ONCE(!sg_cnt);
+
  	/*
  	 * Skip to the S/G entry that sg_offset falls into:
  	 */

diff --git a/drivers/infiniband/ulp/srpt/ib_srpt.c 

b/drivers/infiniband/ulp/srpt/ib_srpt.c
index 3cadf1295417..d9e3d52eb952 100644

--- a/drivers/infiniband/ulp/srpt/ib_srpt.c
+++ b/drivers/infiniband/ulp/srpt/ib_srpt.c

@@ -911,11 +911,16 @@ static int srpt_alloc_rw_ctxs(struct 

srpt_send_ioctx *ioctx,
  		u32 size = be32_to_cpu(db->len);
  		u32 rkey = be32_to_cpu(db->key);

+		WARN_ON_ONCE(!size);
+
  		ret = target_alloc_sgl(&ctx->sg, &ctx->nents, size,
  				 false, i < nbufs - 1);
  		if (ret)
  			goto unwind;

+		WARN_ONCE(ctx->nents <= 0, "%u bytes -> %d entries\n",
+			  size, ctx->nents);
+
  		ret = rdma_rw_ctx_init(&ctx->rw, ch->qp,
                                 ch->sport->port,
  				ctx->sg, ctx->nents, 0, remote_addr,
                                 rkey, dir);
  		if (ret < 0) {