netdev - [PATCH v2 net-next 3/7] dpaa2-eth: Remove preempt_disable() from seed

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Date:   Fri,  7 Jun 2019 21:20:36 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     netdev@...r.kernel.org
Cc:     tglx@...utronix.de, "David S. Miller" <davem@...emloft.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ioana Radulescu <ruxandra.radulescu@....com>
Subject: [PATCH v2 net-next 3/7] dpaa2-eth: Remove preempt_disable() from seed_pool()

According to the comment, the preempt_disable() statement is required
due to synchronisation in napi_alloc_frag(). The awful truth is that
local_bh_disable() is required because otherwise the NAPI poll callback
can be invoked while the open function setup buffers. This isn't
unlikely since the dpaa2 provides multiple devices.

The usage of napi_alloc_frag() has been removed in commit

 27c874867c4e9 ("dpaa2-eth: Use a single page per Rx buffer")

which means that the comment is not accurate and the preempt_disable()
statement is not required.

Remove the outdated comment and the no longer required
preempt_disable().

Cc: Ioana Radulescu <ruxandra.radulescu@....com>
Acked-by: Ioana Radulescu <ruxandra.radulescu@....com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
index 7d2390e3df772..bcd3ceb5f9dc4 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
@@ -997,13 +997,6 @@ static int seed_pool(struct dpaa2_eth_priv *priv, u16 bpid)
 	int i, j;
 	int new_count;
 
-	/* This is the lazy seeding of Rx buffer pools.
-	 * dpaa2_add_bufs() is also used on the Rx hotpath and calls
-	 * napi_alloc_frag(). The trouble with that is that it in turn ends up
-	 * calling this_cpu_ptr(), which mandates execution in atomic context.
-	 * Rather than splitting up the code, do a one-off preempt disable.
-	 */
-	preempt_disable();
 	for (j = 0; j < priv->num_channels; j++) {
 		for (i = 0; i < DPAA2_ETH_NUM_BUFS;
 		     i += DPAA2_ETH_BUFS_PER_CMD) {
@@ -1011,12 +1004,10 @@ static int seed_pool(struct dpaa2_eth_priv *priv, u16 bpid)
 			priv->channel[j]->buf_count += new_count;
 
 			if (new_count < DPAA2_ETH_BUFS_PER_CMD) {
-				preempt_enable();
 				return -ENOMEM;
 			}
 		}
 	}
-	preempt_enable();
 
 	return 0;
 }
-- 
2.20.1