Subject: Re: [PATCH net-next V2 3/4] net/mlx4_core: Use RCU to perform radix tree lookup for SRQ

From: Leon Romanovsky <[email-masked]>
Date: Tue, 20 Sep 2016 16:05:41 +0300

On Tue, Sep 20, 2016 at 03:47:49PM +0300, Sergei Shtylyov wrote:
> Hello.
>
> On 9/20/2016 2:39 PM, Tariq Toukan wrote:
>
> >From: Leon Romanovsky <[email-masked]>
> >
> >Radix tree lookup can be performed without locking.
> >
> >Fixes: 225c7b1feef1 ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
> >Signed-off-by: Leon Romanovsky <[email-masked]>
> >Suggested-by: Sagi Grimberg <[email-masked]>
> >Signed-off-by: Tariq Toukan <[email-masked]>
> >---
> > drivers/net/ethernet/mellanox/mlx4/srq.c | 14 +++++---------
> > 1 file changed, 5 insertions(+), 9 deletions(-)
> >
> >diff --git a/drivers/net/ethernet/mellanox/mlx4/srq.c b/drivers/net/ethernet/mellanox/mlx4/srq.c
> >index 67146624eb58..f44d089e2ca6 100644
> >--- a/drivers/net/ethernet/mellanox/mlx4/srq.c
> >+++ b/drivers/net/ethernet/mellanox/mlx4/srq.c
> >@@ -45,15 +45,12 @@ void mlx4_srq_event(struct mlx4_dev *dev, u32 srqn, int event_type)
> > 	struct mlx4_srq_table *srq_table = &mlx4_priv(dev)->srq_table;
> > 	struct mlx4_srq *srq;
> >
> >-	spin_lock(&srq_table->lock);
> >-
> >+	rcu_read_lock();
> > 	srq = radix_tree_lookup(&srq_table->tree, srqn & (dev->caps.num_srqs - 1));
> >+	rcu_read_unlock();
> > 	if (srq)
> > 		atomic_inc(&srq->refcount);
> >-
> >-	spin_unlock(&srq_table->lock);
> >-
> >-	if (!srq) {
> >+	else {
> > 		mlx4_warn(dev, "Async event for bogus SRQ %08x\n", srqn);
> > 		return;
> > 	}
>
>    CodingStyle: all branches of the *if* statement should have {} if at
> least one has.

I'm not arguing, but wanted to raise attention that checkpatch.pl
doesn't warn about it.

➜  /tmp wget https://patchwork.ozlabs.org/patch/672216/mbox/
➜  linux-rdma git:(master) ./scripts/checkpatch.pl /tmp/index.html
total: 0 errors, 0 warnings, 0 checks, 32 lines checked

/tmp/index.html has no obvious style problems and is ready for
submission.

And CodingStyle presents a little bit different case
----
This does not apply if only one branch of a conditional statement is a
single statement; in the latter case use braces in both branches:

        if (condition) {
                do_this();
                do_that();
        } else {
                otherwise();
        }

and not

        if (condition)
                do_that();
        else {
                otherwise();
		otherwise();
        }

Thanks