linux-kernel - Re: [PATCH 2/2] infiniband: Modify the reference to xa_store_irq() because the parameter of this function has changed

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Date:   Wed, 4 Nov 2020 14:58:43 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "xiaofeng.yan" <xiaofeng.yan2012@...il.com>
Cc:     willy@...radead.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, dledford@...hat.com,
        oulijun@...wei.com, yanxiaofeng7@...com
Subject: Re: [PATCH 2/2] infiniband: Modify the reference to xa_store_irq()
 because the parameter of this function  has changed

On Wed, Nov 04, 2020 at 10:32:13AM +0800, xiaofeng.yan wrote:
> From: "xiaofeng.yan" <yanxiaofeng7@...com>
> 
> function xa_store_irq() has three parameters because of removing
> patameter "gfp_t gfp"
> 
> Signed-off-by: xiaofeng.yan <yanxiaofeng7@...com>
>  drivers/infiniband/core/cm.c            | 2 +-
>  drivers/infiniband/hw/hns/hns_roce_qp.c | 2 +-
>  drivers/infiniband/hw/mlx5/srq_cmd.c    | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
> index 5740d1ba3568..afcb5711270b 100644
> +++ b/drivers/infiniband/core/cm.c
> @@ -879,7 +879,7 @@ static struct cm_id_private *cm_alloc_id_priv(struct ib_device *device,
>  static void cm_finalize_id(struct cm_id_private *cm_id_priv)
>  {
>  	xa_store_irq(&cm.local_id_table, cm_local_id(cm_id_priv->id.local_id),
> -		     cm_id_priv, GFP_KERNEL);
> +		     cm_id_priv);
>  }

This one is almost a bug, the entry is preallocated with NULL though:

	ret = xa_alloc_cyclic_irq(&cm.local_id_table, &id, NULL, xa_limit_32b,
				  &cm.local_id_next, GFP_KERNEL);

so it should never allocate here:

static int cm_req_handler(struct cm_work *work)
{
	spin_lock_irq(&cm_id_priv->lock);
	cm_finalize_id(cm_id_priv);

Still, woops.

Matt, maybe a might_sleep is deserved in here someplace?

@@ -1534,6 +1534,8 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
        XA_STATE(xas, xa, index);
        void *curr;
 
+       might_sleep_if(gfpflags_allow_blocking(gfp));
+
        if (WARN_ON_ONCE(xa_is_advanced(entry)))
                return XA_ERROR(-EINVAL);
        if (xa_track_free(xa) && !entry)

And similar in the other places that conditionally call __xas_nomem()
?

I also still wish there was a proper 'xa store in already allocated
but null' idiom - I remember you thought about using gfp flags == 0 at
one point.

Jason