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authorVladimir Oltean <vladimir.oltean@nxp.com>2021-04-09 22:27:59 +0300
committerJakub Kicinski <kuba@kernel.org>2021-04-10 04:17:12 +0300
commita93580a02dbf9e67c4f801e2ff1b32ec4c748516 (patch)
treece11238d71fe248676ee0711b93eb21203998c4a
parent95b5c291322be25431391d08020db0138631c8b2 (diff)
downloadlinux-a93580a02dbf9e67c4f801e2ff1b32ec4c748516.tar.xz
net: enetc: fix TX ring interrupt storm
The blamed commit introduced a bit in the TX software buffer descriptor structure for determining whether a BD is final or not; we rearm the TX interrupt vector for every frame (hence final BD) transmitted. But there is a problem with the patch: it replaced a condition whose expression is a bool which was evaluated at the beginning of the "while" loop with a bool expression that is evaluated on the spot: tx_swbd->is_eof. The problem with the latter expression is that the tx_swbd has already been incremented at that stage, so the tx_swbd->is_eof check is in fact with the _next_ software BD. Which is _not_ final. The effect is that the CPU is in 100% load with ksoftirqd because it does not acknowledge the TX interrupt, so the handler keeps getting called again and again. The fix is to restore the code structure, and keep the local bool is_eof variable, just to assign it the tx_swbd->is_eof value instead of !!tx_swbd->skb. Fixes: d504498d2eb3 ("net: enetc: add a dedicated is_eof bit in the TX software BD") Reported-by: Alex Marginean <alexandru.marginean@nxp.com> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com> Link: https://lore.kernel.org/r/20210409192759.3895104-1-olteanv@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
-rw-r--r--drivers/net/ethernet/freescale/enetc/enetc.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index d86395775ed0..182d808451bd 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -406,6 +406,7 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
while (bds_to_clean && tx_frm_cnt < ENETC_DEFAULT_TX_WORK) {
struct xdp_frame *xdp_frame = enetc_tx_swbd_get_xdp_frame(tx_swbd);
struct sk_buff *skb = enetc_tx_swbd_get_skb(tx_swbd);
+ bool is_eof = tx_swbd->is_eof;
if (unlikely(tx_swbd->check_wb)) {
struct enetc_ndev_priv *priv = netdev_priv(ndev);
@@ -453,7 +454,7 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
}
/* BD iteration loop end */
- if (tx_swbd->is_eof) {
+ if (is_eof) {
tx_frm_cnt++;
/* re-arm interrupt source */
enetc_wr_reg_hot(tx_ring->idr, BIT(tx_ring->index) |