Re: [PATCH] net/sched: Set the flushing flags to false to prevent an infinite loop
From: Pedro Tammela
Date: Wed Jun 07 2023 - 11:02:37 EST
On 07/06/2023 01:19, renmingshuai wrote:
On 06/06/2023 11:45, renmingshuai wrote:
When a new chain is added by using tc, one soft lockup alarm will be
generated after delete the prio 0 filter of the chain. To reproduce
the problem, perform the following steps:
(1) tc qdisc add dev eth0 root handle 1: htb default 1
(2) tc chain add dev eth0
(3) tc filter del dev eth0 chain 0 parent 1: prio 0
(4) tc filter add dev eth0 chain 0 parent 1:
This seems like it could be added to tdc or 3 and 4 must be run in parallel?
3 and 4 do not need to be run inparallel. When a new chain is added by the
way as step 1 and the step 3 is completed, this problem always occurs
whenever step 4 is run.
Got it,
The test still hangs with the provided patch.
+ tc qdisc add dev lo root handle 1: htb default 1
+ tc chain add dev lo
+ tc filter del dev lo chain 0 parent 1: prio 0
[ 68.790030][ T6704] [+]
[ 68.790060][ T6704] chain refcnt 2
[ 68.790951][ T6704] [-]
+ tc filter add dev lo chain 0 parent 1:
<hangs>
Also please add this test to tdc, it should be straightforward.
The refcnt of the chain added by step 2 is equal to 1. After step 3,
the flushing flag of the chain is set to true in the tcf_chain_flush()
called by tc_del_tfilter() because the prio is 0. In this case, if
we add a new filter to this chain, it will never succeed and try again
and again because the refresh flash is always true and refcnt is 1.
A soft lock alarm is generated 20 seconds later.
The stack is show as below:
Kernel panic - not syncing: softlockup: hung tasks
CPU: 2 PID: 3321861 Comm: tc Kdump: loaded Tainted: G
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
Call Trace:
<IRQ>
dump_stack+0x57/0x6e
panic+0x196/0x3ec
watchdog_timer_fn.cold+0x16/0x5c
__run_hrtimer+0x5e/0x190
__hrtimer_run_queues+0x8a/0xe0
hrtimer_interrupt+0x110/0x2c0
? irqtime_account_irq+0x49/0xf0
__sysvec_apic_timer_interrupt+0x5f/0xe0
asm_call_irq_on_stack+0x12/0x20
</IRQ>
sysvec_apic_timer_interrupt+0x72/0x80
asm_sysvec_apic_timer_interrupt+0x12/0x20
RIP: 0010:mutex_lock+0x24/0x70
RSP: 0018:ffffa836004ab9a8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff95bb02d76700 RCX: 0000000000000000
RDX: ffff95bb27462100 RSI: 0000000000000000 RDI: ffff95ba5b527000
RBP: ffff95ba5b527000 R08: 0000000000000001 R09: ffffa836004abbb8
R10: 000000000000000f R11: 0000000000000000 R12: 0000000000000000
R13: ffff95ba5b527000 R14: ffffa836004abbb8 R15: 0000000000000001
__tcf_chain_put+0x27/0x200
tc_new_tfilter+0x5e8/0x810
? tc_setup_cb_add+0x210/0x210
rtnetlink_rcv_msg+0x2e3/0x380
? rtnl_calcit.isra.0+0x120/0x120
netlink_rcv_skb+0x50/0x100
netlink_unicast+0x12d/0x1d0
netlink_sendmsg+0x286/0x490
sock_sendmsg+0x62/0x70
____sys_sendmsg+0x24c/0x2c0
? import_iovec+0x17/0x20
? sendmsg_copy_msghdr+0x80/0xa0
___sys_sendmsg+0x75/0xc0
? do_fault_around+0x118/0x160
? do_read_fault+0x68/0xf0
? __handle_mm_fault+0x3f9/0x6f0
__sys_sendmsg+0x59/0xa0
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x61/0xc6
RIP: 0033:0x7f96705b8247
RSP: 002b:00007ffe552e9dc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f96705b8247
RDX: 0000000000000000 RSI: 00007ffe552e9e40 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000558113f678b0
R10: 00007f967069ab00 R11: 0000000000000246 R12: 00000000647ea089
R13: 00007ffe552e9f30 R14: 0000000000000001 R15: 0000558113175f00
To avoid this case, set chain->flushing to be false if the chain->refcnt
is 1 after flushing the chain when prio is 0.
Fixes: 726d061286ce ("net: sched: prevent insertion of new classifiers during chain flush")
Signed-off-by: Ren Mingshuai <renmingshuai@xxxxxxxxxx>
---
net/sched/cls_api.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 2621550bfddc..68be55d75831 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -2442,6 +2442,13 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
tfilter_notify_chain(net, skb, block, q, parent, n,
chain, RTM_DELTFILTER, extack);
tcf_chain_flush(chain, rtnl_held);
+ /* Set the flushing flags to false to prevent an infinite loop
+ * when a new filter is added.
+ */
+ mutex_lock(&chain->filter_chain_lock);
+ if (chain->refcnt == 1)
+ chain->flushing = false;
+ mutex_unlock(&chain->filter_chain_lock);
err = 0;
goto errout;
}