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From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
To: netdev@vger.kernel.org, linyunsheng@huawei.com
Cc: "David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Eric Dumazet" <edumazet@google.com>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Antoine Tenart" <atenart@kernel.org>,
	"Alexander Lobakin" <alobakin@pm.me>,
	"Wei Wang" <weiwan@google.com>, "Taehee Yoo" <ap420073@gmail.com>,
	"Björn Töpel" <bjorn@kernel.org>, "Arnd Bergmann" <arnd@arndb.de>,
	"Kumar Kartikeya Dwivedi" <memxor@gmail.com>,
	"Neil Horman" <nhorman@redhat.com>,
	"Dust Li" <dust.li@linux.alibaba.com>
Subject: [PATCH net v2] napi: fix race inside napi_enable
Date: Sat, 18 Sep 2021 16:52:32 +0800	[thread overview]
Message-ID: <20210918085232.71436-1-xuanzhuo@linux.alibaba.com> (raw)

The process will cause napi.state to contain NAPI_STATE_SCHED and
not in the poll_list, which will cause napi_disable() to get stuck.

The prefix "NAPI_STATE_" is removed in the figure below, and
NAPI_STATE_HASHED is ignored in napi.state.

                      CPU0       |                   CPU1       | napi.state
===============================================================================
napi_disable()                   |                              | SCHED | NPSVC
napi_enable()                    |                              |
{                                |                              |
    smp_mb__before_atomic();     |                              |
    clear_bit(SCHED, &n->state); |                              | NPSVC
                                 | napi_schedule_prep()         | SCHED | NPSVC
                                 | napi_poll()                  |
                                 |   napi_complete_done()       |
                                 |   {                          |
                                 |      if (n->state & (NPSVC | | (1)
                                 |               _BUSY_POLL)))  |
                                 |           return false;      |
                                 |     ................         |
                                 |   }                          | SCHED | NPSVC
                                 |                              |
    clear_bit(NPSVC, &n->state); |                              | SCHED
}                                |                              |
                                 |                              |
napi_schedule_prep()             |                              | SCHED | MISSED (2)

(1) Here return direct. Because of NAPI_STATE_NPSVC exists.
(2) NAPI_STATE_SCHED exists. So not add napi.poll_list to sd->poll_list

Since NAPI_STATE_SCHED already exists and napi is not in the
sd->poll_list queue, NAPI_STATE_SCHED cannot be cleared and will always
exist.

1. This will cause this queue to no longer receive packets.
2. If you encounter napi_disable under the protection of rtnl_lock, it
   will cause the entire rtnl_lock to be locked, affecting the overall
   system.

This patch uses cmpxchg to implement napi_enable(), which ensures that
there will be no race due to the separation of clear two bits.

Fixes: 2d8bff12699abc ("netpoll: Close race condition between poll_one_napi and napi_disable")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
---
 net/core/dev.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 74fd402d26dd..7ee9fecd3aff 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6923,12 +6923,16 @@ EXPORT_SYMBOL(napi_disable);
  */
 void napi_enable(struct napi_struct *n)
 {
-	BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
-	smp_mb__before_atomic();
-	clear_bit(NAPI_STATE_SCHED, &n->state);
-	clear_bit(NAPI_STATE_NPSVC, &n->state);
-	if (n->dev->threaded && n->thread)
-		set_bit(NAPI_STATE_THREADED, &n->state);
+	unsigned long val, new;
+
+	do {
+		val = READ_ONCE(n->state);
+		BUG_ON(!test_bit(NAPI_STATE_SCHED, &val));
+
+		new = val & ~(NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC);
+		if (n->dev->threaded && n->thread)
+			new |= NAPIF_STATE_THREADED;
+	} while (cmpxchg(&n->state, val, new) != val);
 }
 EXPORT_SYMBOL(napi_enable);
 
-- 
2.31.0


             reply	other threads:[~2021-09-18  8:52 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-18  8:52 Xuan Zhuo [this message]
2021-09-20  8:50 ` patchwork-bot+netdevbpf
2021-09-20 19:20 ` Jakub Kicinski
2021-09-22  6:47   ` Xuan Zhuo
2021-09-23 13:14     ` Jakub Kicinski
     [not found]       ` <1632404456.506512-1-xuanzhuo@linux.alibaba.com>
2021-09-23 14:54         ` Jakub Kicinski
2021-10-18 21:58 ` Sukadev Bhattiprolu
2021-10-18 22:55   ` Jakub Kicinski
2021-10-18 23:36     ` Dany Madden
2021-10-18 23:47       ` Jakub Kicinski
2021-10-19  0:01         ` Sukadev Bhattiprolu
2021-10-22  3:16       ` Sukadev Bhattiprolu
2021-10-25 17:36         ` Jakub Kicinski

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