linux-kernel - Re: [PATCH RFC] iw_cxgb4: drop check

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Date:   Thu, 24 Jan 2019 02:53:52 +0100
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Steve Wise <swise@...ngridcomputing.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Nicholas Mc Guire <hofrat@...dl.org>,
        Doug Ledford <dledford@...hat.com>,
        Raju Rangoju <rajur@...lsio.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] iw_cxgb4: drop check - dead code

On Wed, Jan 23, 2019 at 12:45:11PM -0600, Steve Wise wrote:
> 
> 
> On 1/23/2019 12:30 PM, Jason Gunthorpe wrote:
> > On Sun, Jan 20, 2019 at 02:27:13AM +0100, Nicholas Mc Guire wrote:
> >> The kmalloc is called with  | __GFP_NOFAIL  so there is no point in
> >> checking the return value - it either returns valid storage or it would
> >> hang/terminate there. But it is not possible to say if the use of
> >> __GFP_NOFAIL is really needed and the check should be removed or
> >> vice-versa (use of __GFP_NOFAIL should be only in exceptional
> >> cases as I understand it and alloc_srq_queue() is called in quite
> >> a few places)
> >> In either way it would need fixing.
> >>
> >> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> >> Fixes: 6a0b6174d35a ("rdma/cxgb4: Add support for kernel mode SRQ's")
> >> ---
> > 
> > Steve? It seems weird to have NOFAIL and then have an error unwind
> > path, what is the deal here?
> > 
> >> diff --git a/drivers/infiniband/hw/cxgb4/qp.c b/drivers/infiniband/hw/cxgb4/qp.c
> >> index 917ce5c..c2a12ba 100644
> >> --- a/drivers/infiniband/hw/cxgb4/qp.c
> >> +++ b/drivers/infiniband/hw/cxgb4/qp.c
> >> @@ -2597,8 +2597,6 @@ static int alloc_srq_queue(struct c4iw_srq *srq, struct c4iw_dev_ucontext *uctx,
> >>  	wr_len = sizeof(*res_wr) + sizeof(*res);
> >>  
> >>  	skb = alloc_skb(wr_len, GFP_KERNEL | __GFP_NOFAIL);
> >> -	if (!skb)
> >> -		goto err_free_queue;
> >>  	set_wr_txq(skb, CPL_PRIORITY_CONTROL, 0);
> >>  
> >>  	res_wr = (struct fw_ri_res_wr *)__skb_put(skb, wr_len);
> >> -- 
> >> 2.1.4
> >>
> 
> The other queue allocations in qp.c don't use __GFP_NOFAIL.  So either
> leave it and remove the error check as per this patch, or remove the
> NOFAIL and leave the check.
> 
> I suggest you remove the __GFP_NOFAIL, since I have a recollection that
> using it was frowned upon.  In this case, if there is no memory
> available it is reasonable to return that error to the user creating the
> srq...
>
thanks for taking care of this - I simply did not have enough
context to decide if there would be some special reason
for this allocation to need __GFP_NOFAIL - keeping its use
to a minimum though is the best solution.

thx!
hofrat