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

On Tue, Sep 20, 2016 at 03:47:49PM +0300, Sergei Shtylyov wrote:

Hello.

On 9/20/2016 2:39 PM, Tariq Toukan wrote:

quoted

From: Leon Romanovsky <redacted>

Radix tree lookup can be performed without locking.

Fixes: 225c7b1feef1 ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
Signed-off-by: Leon Romanovsky <redacted>
Suggested-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Tariq Toukan <redacted>
---
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