netdev - [PATCH] net: Prevent multiple NAPI instances co-existing in the list

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Date:	Thu, 8 Jan 2015 16:22:54 +0800
From:	Dennis Chen <kernel.org.gnu@...il.com>
To:	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Dennis Chen <kernel.org.gnu@...il.com>
Subject: [PATCH] net: Prevent multiple NAPI instances co-existing in the list

Some drivers may clear the NAPI_STATE_SCHED bit upon the state of the
NAPI instance after exhaust the budget in the poll function, which
will open a window for next device interrupt handler to insert a same
instance to the list after calling list_add_tail(&n->poll_list,
repoll) if we don't set this bit.

Signed-off-by: Dennis Chen <kernel.org.gnu@...il.com>
---
 net/core/dev.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 683d493..b3107ac 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4619,6 +4619,14 @@ static int napi_poll(struct napi_struct *n,
struct list_head *repoll)
                             n->dev ? n->dev->name : "backlog");
                goto out_unlock;
        }
+
+       /* Some drivers may exit the polling mode when exhaust the
+        * budget. Set the NAPI_STATE_SCHED bit to prevent multiple NAPI
+        * instances in the list in case of next device interrupt raised.
+        */
+       if (unlikely(!test_and_set_bit(NAPI_STATE_SCHED, &n->state)))
+               pr_warn_once("%s: exit polling mode after exhaust the budget\n",
+                            n->dev ? n->dev->name : "backlog");

        list_add_tail(&n->poll_list, repoll);

-- 
1.7.9.5

-- 
Den
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