netdev - [PATCH net 2/2] net: gro: Let the timeout timer expire in softirq context with `threadirqs'

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Message-Id: <20191126222013.1904785-3-bigeasy@linutronix.de>
Date:   Tue, 26 Nov 2019 23:20:13 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 2/2] net: gro: Let the timeout timer expire in softirq context with `threadirqs'

The timer callback (napi_watchdog()) invokes __napi_schedule_irqoff()
with disabled interrupts. With the `threadirqs' commandline option all
interrupt handler are threaded and using __napi_schedule_irqoff() is not
an issue because everyone is using it in threaded context which is
synchronised with local_bh_disable().
The napi_watchdog() timer is still expiring in hardirq context and may
interrupt a threaded handler which is in the middle of
__napi_schedule_irqoff() leading to list corruption.

Let the napi_watchdog() expire in softirq context if `threadirqs' is
used.

Fixes: 3b47d30396bae ("net: gro: add a per device gro flush timer")
Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 net/core/dev.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 99ac84ff398f4..ec533d20931bc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5994,6 +5994,8 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 		napi_gro_flush(n, !!timeout);
 		if (timeout)
 			hrtimer_start(&n->timer, ns_to_ktime(timeout),
+				      force_irqthreads ?
+				      HRTIMER_MODE_REL_PINNED_SOFT :
 				      HRTIMER_MODE_REL_PINNED);
 	}
 	if (unlikely(!list_empty(&n->poll_list))) {
@@ -6225,7 +6227,9 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 		    int (*poll)(struct napi_struct *, int), int weight)
 {
 	INIT_LIST_HEAD(&napi->poll_list);
-	hrtimer_init(&napi->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
+	hrtimer_init(&napi->timer, CLOCK_MONOTONIC,
+		     force_irqthreads ?
+		     HRTIMER_MODE_REL_PINNED_SOFT : HRTIMER_MODE_REL_PINNED);
 	napi->timer.function = napi_watchdog;
 	init_gro_hash(napi);
 	napi->skb = NULL;
-- 
2.24.0