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

[Leon Romanovsky]

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 <leo...@mellanox.com>
> >
> >Radix tree lookup can be performed without locking.
> >
> >Fixes: 225c7b1feef1 ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand 
> >adapters")
> >Signed-off-by: Leon Romanovsky <leo...@mellanox.com>
> >Suggested-by: Sagi Grimberg <s...@grimberg.me>
> >Signed-off-by: Tariq Toukan <tar...@mellanox.com>
> >---
> > 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

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