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I triggered it when running command `./tdc.py -f tc-tests/infra/qdiscs.json` Could you take a look? I don't have much time now, since I am still finalizing my netem duplicate patches. Thanks! ------------------------------------> Test 5e6d: Test QFQ's enqueue reentrant behaviour with netem [ 1066.410119] ================================================================== [ 1066.411114] BUG: KASAN: null-ptr-deref in qfq_dequeue+0x1e4/0x5a1 [ 1066.412305] Read of size 8 at addr 0000000000000048 by task ping/945 [ 1066.413136] [ 1066.413426] CPU: 0 UID: 0 PID: 945 Comm: ping Tainted: G W 6.16.0-rc5+ #542 PREEMPT(voluntary) [ 1066.413459] Tainted: [W]=WARN [ 1066.413468] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014 [ 1066.413476] Call Trace: [ 1066.413499] [ 1066.413502] dump_stack_lvl+0x65/0x90 [ 1066.413502] kasan_report+0x85/0xab [ 1066.413502] ? qfq_dequeue+0x1e4/0x5a1 [ 1066.413502] qfq_dequeue+0x1e4/0x5a1 [ 1066.413502] ? __pfx_qfq_dequeue+0x10/0x10 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? lock_acquired+0xde/0x10b [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? sch_direct_xmit+0x1a7/0x390 [ 1066.413502] ? __pfx_sch_direct_xmit+0x10/0x10 [ 1066.413502] dequeue_skb+0x411/0x7a8 [ 1066.413502] __qdisc_run+0x94/0x193 [ 1066.413502] ? __pfx___qdisc_run+0x10/0x10 [ 1066.413502] ? find_held_lock+0x2b/0x71 [ 1066.413502] ? __dev_xmit_skb+0x27c/0x45e [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? rcu_is_watching+0x1c/0x3c [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? dev_qdisc_enqueue+0x117/0x14c [ 1066.413502] __dev_xmit_skb+0x3b9/0x45e [ 1066.413502] ? __pfx___dev_xmit_skb+0x10/0x10 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __pfx_rcu_read_lock_bh_held+0x10/0x10 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] __dev_queue_xmit+0xa14/0xbe2 [ 1066.413502] ? look_up_lock_class+0xb0/0x10d [ 1066.413502] ? __pfx___dev_queue_xmit+0x10/0x10 [ 1066.413502] ? validate_chain+0x4b/0x261 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __lock_acquire+0x71d/0x7b1 [ 1066.413502] ? neigh_resolve_output+0x13b/0x1d7 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? lock_acquire.part.0+0xb0/0x1c6 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? find_held_lock+0x2b/0x71 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? local_clock_noinstr+0x32/0x9c [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? mark_lock+0x6d/0x14d [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __asan_memcpy+0x38/0x59 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? eth_header+0x92/0xd1 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? neigh_resolve_output+0x188/0x1d7 [ 1066.413502] ip_finish_output2+0x58b/0x5c3 [ 1066.413502] ip_send_skb+0x25/0x5f [ 1066.413502] raw_sendmsg+0x9dc/0xb60 [ 1066.413502] ? __pfx_raw_sendmsg+0x10/0x10 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? stack_trace_save+0x8b/0xbb [ 1066.413502] ? kasan_save_stack+0x1c/0x38 [ 1066.413502] ? kasan_record_aux_stack+0x87/0x91 [ 1066.413502] ? __might_fault+0x72/0xbe [ 1066.413502] ? __ww_mutex_die.part.0+0xe/0x88 [ 1066.413502] ? __might_fault+0x72/0xbe [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? find_held_lock+0x2b/0x71 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? local_clock_noinstr+0x32/0x9c [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __lock_release.isra.0+0xdb/0x197 [ 1066.413502] ? __might_fault+0x72/0xbe [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? inet_send_prepare+0x18/0x5d [ 1066.413502] sock_sendmsg_nosec+0x82/0xe2 [ 1066.413502] __sys_sendto+0x175/0x1cc [ 1066.413502] ? __pfx___sys_sendto+0x10/0x10 [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __might_fault+0x72/0xbe [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? local_clock_noinstr+0x32/0x9c [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __lock_release.isra.0+0xdb/0x197 [ 1066.413502] ? __might_fault+0x72/0xbe [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? lock_release+0xde/0x10b [ 1066.413502] ? srso_return_thunk+0x5/0x5f [ 1066.413502] ? __do_sys_gettimeofday+0xb3/0x112 [ 1066.413502] __x64_sys_sendto+0x76/0x86 [ 1066.413502] do_syscall_64+0x94/0x209 [ 1066.413502] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 1066.413502] RIP: 0033:0x7fb9f917ce27 [ 1066.413502] Code: c7 c0 ff ff ff ff eb be 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 80 3d 45 85 0c 00 00 41 89 ca 74 10 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 69 c3 55 48 89 e5 53 48 83 ec 38 44 89 4d d0 [ 1066.413502] RSP: 002b:00007ffeb9932798 EFLAGS: 00000202 ORIG_RAX: 000000000000002c [ 1066.413502] RAX: ffffffffffffffda RBX: 000056476e3550a0 RCX: 00007fb9f917ce27 [ 1066.413502] RDX: 0000000000000040 RSI: 000056476ea11320 RDI: 0000000000000003 [ 1066.413502] RBP: 00007ffeb99327e0 R08: 000056476e357320 R09: 0000000000000010 [ 1066.413502] R10: 0000000000000000 R11: 0000000000000202 R12: 000056476ea11320 [ 1066.413502] R13: 0000000000000040 R14: 00007ffeb9933e98 R15: 00007ffeb9933e98 [ 1066.413502] [ 1066.413502] ==================================================================