linux/include/net/sch_generic.h, branch v6.17

net/sched: Fix backlog accounting in qdisc_dequeue_internal

2025-08-15T00:52:29Z

This issue applies for the following qdiscs: hhf, fq, fq_codel, and fq_pie, and occurs in their change handlers when adjusting to the new limit. The problem is the following in the values passed to the subsequent qdisc_tree_reduce_backlog call given a tbf parent: When the tbf parent runs out of tokens, skbs of these qdiscs will be placed in gso_skb. Their peek handlers are qdisc_peek_dequeued, which accounts for both qlen and backlog. However, in the case of qdisc_dequeue_internal, ONLY qlen is accounted for when pulling from gso_skb. This means that these qdiscs are missing a qdisc_qstats_backlog_dec when dropping packets to satisfy the new limit in their change handlers. One can observe this issue with the following (with tc patched to support a limit of 0): export TARGET=fq tc qdisc del dev lo root tc qdisc add dev lo root handle 1: tbf rate 8bit burst 100b latency 1ms tc qdisc replace dev lo handle 3: parent 1:1 $TARGET limit 1000 echo ''; echo 'add child'; tc -s -d qdisc show dev lo ping -I lo -f -c2 -s32 -W0.001 127.0.0.1 2>&1 >/dev/null echo ''; echo 'after ping'; tc -s -d qdisc show dev lo tc qdisc change dev lo handle 3: parent 1:1 $TARGET limit 0 echo ''; echo 'after limit drop'; tc -s -d qdisc show dev lo tc qdisc replace dev lo handle 2: parent 1:1 sfq echo ''; echo 'post graft'; tc -s -d qdisc show dev lo The second to last show command shows 0 packets but a positive number (74) of backlog bytes. The problem becomes clearer in the last show command, where qdisc_purge_queue triggers qdisc_tree_reduce_backlog with the positive backlog and causes an underflow in the tbf parent's backlog (4096 Mb instead of 0). To fix this issue, the codepath for all clients of qdisc_dequeue_internal has been simplified: codel, pie, hhf, fq, fq_pie, and fq_codel. qdisc_dequeue_internal handles the backlog adjustments for all cases that do not directly use the dequeue handler. The old fq_codel_change limit adjustment loop accumulated the arguments to the subsequent qdisc_tree_reduce_backlog call through the cstats field. However, this is confusing and error prone as fq_codel_dequeue could also potentially mutate this field (which qdisc_dequeue_internal calls in the non gso_skb case), so we have unified the code here with other qdiscs. Fixes: 2d3cbfd6d54a ("net_sched: Flush gso_skb list too during ->change()") Fixes: 4b549a2ef4be ("fq_codel: Fair Queue Codel AQM") Fixes: 10239edf86f1 ("net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc") Signed-off-by: William Liu Reviewed-by: Savino Dicanosa Link: https://patch.msgid.link/20250812235725.45243-1-will@willsroot.io Signed-off-by: Jakub Kicinski

net_sched: remove qdisc_tree_flush_backlog()

2025-06-12T15:05:50Z

This function is no longer used after the four prior fixes. Given all prior uses were wrong, it seems better to remove it. Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20250611111515.1983366-6-edumazet@google.com Signed-off-by: Jakub Kicinski

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2025-05-15T18:28:30Z

Cross-merge networking fixes after downstream PR (net-6.15-rc7). Conflicts: tools/testing/selftests/drivers/net/hw/ncdevmem.c 97c4e094a4b2 ("tests/ncdevmem: Fix double-free of queue array") 2f1a805f32ba ("selftests: ncdevmem: Implement devmem TCP TX") https://lore.kernel.org/20250514122900.1e77d62d@canb.auug.org.au Adjacent changes: net/core/devmem.c net/core/devmem.h 0afc44d8cdf6 ("net: devmem: fix kernel panic when netlink socket close after module unload") bd61848900bf ("net: devmem: Implement TX path") Signed-off-by: Jakub Kicinski

net_sched: Flush gso_skb list too during ->change()

2025-05-09T11:34:38Z

Previously, when reducing a qdisc's limit via the ->change() operation, only the main skb queue was trimmed, potentially leaving packets in the gso_skb list. This could result in NULL pointer dereference when we only check sch->limit against sch->q.qlen. This patch introduces a new helper, qdisc_dequeue_internal(), which ensures both the gso_skb list and the main queue are properly flushed when trimming excess packets. All relevant qdiscs (codel, fq, fq_codel, fq_pie, hhf, pie) are updated to use this helper in their ->change() routines. Fixes: 76e3cc126bb2 ("codel: Controlled Delay AQM") Fixes: 4b549a2ef4be ("fq_codel: Fair Queue Codel AQM") Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler") Fixes: ec97ecf1ebe4 ("net: sched: add Flow Queue PIE packet scheduler") Fixes: 10239edf86f1 ("net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc") Fixes: d4b36210c2e6 ("net: pkt_sched: PIE AQM scheme") Reported-by: Will Reported-by: Savy Signed-off-by: Cong Wang Signed-off-by: David S. Miller

net: sched: generalize check for no-queue qdisc on TX queue

2025-04-28T21:06:58Z

The "noqueue" qdisc can either be directly attached, or get default attached if net_device priv_flags has IFF_NO_QUEUE. In both cases, the allocated Qdisc structure gets it's enqueue function pointer reset to NULL by noqueue_init() via noqueue_qdisc_ops. This is a common case for software virtual net_devices. For these devices with no-queue, the transmission path in __dev_queue_xmit() will bypass the qdisc layer. Directly invoking device drivers ndo_start_xmit (via dev_hard_start_xmit). In this mode the device driver is not allowed to ask for packets to be queued (either via returning NETDEV_TX_BUSY or stopping the TXQ). The simplest and most reliable way to identify this no-queue case is by checking if enqueue == NULL. The vrf driver currently open-codes this check (!qdisc->enqueue). While functionally correct, this low-level detail is better encapsulated in a dedicated helper for clarity and long-term maintainability. To make this behavior more explicit and reusable, this patch introduce a new helper: qdisc_txq_has_no_queue(). Helper will also be used by the veth driver in the next patch, which introduces optional qdisc-based backpressure. This is a non-functional change. Reviewed-by: David Ahern Reviewed-by: Toke Høiland-Jørgensen Signed-off-by: Jesper Dangaard Brouer Link: https://patch.msgid.link/174559293172.827981.7583862632045264175.stgit@firesoul Signed-off-by: Jakub Kicinski

net: sched: Fix truncation of offloaded action statistics

2025-02-06T02:32:06Z

In case of tc offload, when user space queries the kernel for tc action statistics, tc will query the offloaded statistics from device drivers. Among other statistics, drivers are expected to pass the number of packets that hit the action since the last query as a 64-bit number. Unfortunately, tc treats the number of packets as a 32-bit number, leading to truncation and incorrect statistics when the number of packets since the last query exceeds 0xffffffff: $ tc -s filter show dev swp2 ingress filter protocol all pref 1 flower chain 0 filter protocol all pref 1 flower chain 0 handle 0x1 skip_sw in_hw in_hw_count 1 action order 1: mirred (Egress Redirect to device swp1) stolen index 1 ref 1 bind 1 installed 58 sec used 0 sec Action statistics: Sent 1133877034176 bytes 536959475 pkt (dropped 0, overlimits 0 requeues 0) [...] According to the above, 2111-byte packets were redirected which is impossible as only 64-byte packets were transmitted and the MTU was 1500. Fix by treating packets as a 64-bit number: $ tc -s filter show dev swp2 ingress filter protocol all pref 1 flower chain 0 filter protocol all pref 1 flower chain 0 handle 0x1 skip_sw in_hw in_hw_count 1 action order 1: mirred (Egress Redirect to device swp1) stolen index 1 ref 1 bind 1 installed 61 sec used 0 sec Action statistics: Sent 1370624380864 bytes 21416005951 pkt (dropped 0, overlimits 0 requeues 0) [...] Which shows that only 64-byte packets were redirected (1370624380864 / 21416005951 = 64). Fixes: 380407023526 ("net/sched: Enable netdev drivers to update statistics of offloaded actions") Reported-by: Joe Botha Signed-off-by: Ido Schimmel Reviewed-by: Petr Machata Reviewed-by: Simon Horman Link: https://patch.msgid.link/20250204123839.1151804-1-idosch@nvidia.com Signed-off-by: Jakub Kicinski

net: sched: refine software bypass handling in tc_run

2025-01-20T09:21:27Z

This patch addresses issues with filter counting in block (tcf_block), particularly for software bypass scenarios, by introducing a more accurate mechanism using useswcnt. Previously, filtercnt and skipswcnt were introduced by: Commit 2081fd3445fe ("net: sched: cls_api: add filter counter") and Commit f631ef39d819 ("net: sched: cls_api: add skip_sw counter") filtercnt tracked all tp (tcf_proto) objects added to a block, and skipswcnt counted tp objects with the skipsw attribute set. The problem is: a single tp can contain multiple filters, some with skipsw and others without. The current implementation fails in the case: When the first filter in a tp has skipsw, both skipswcnt and filtercnt are incremented, then adding a second filter without skipsw to the same tp does not modify these counters because tp->counted is already set. This results in bypass software behavior based solely on skipswcnt equaling filtercnt, even when the block includes filters without skipsw. Consequently, filters without skipsw are inadvertently bypassed. To address this, the patch introduces useswcnt in block to explicitly count tp objects containing at least one filter without skipsw. Key changes include: Whenever a filter without skipsw is added, its tp is marked with usesw and counted in useswcnt. tc_run() now uses useswcnt to determine software bypass, eliminating reliance on filtercnt and skipswcnt. This refined approach prevents software bypass for blocks containing mixed filters, ensuring correct behavior in tc_run(). Additionally, as atomic operations on useswcnt ensure thread safety and tp->lock guards access to tp->usesw and tp->counted, the broader lock down_write(&block->cb_lock) is no longer required in tc_new_tfilter(), and this resolves a performance regression caused by the filter counting mechanism during parallel filter insertions. The improvement can be demonstrated using the following script: # cat insert_tc_rules.sh tc qdisc add dev ens1f0np0 ingress for i in $(seq 16); do taskset -c $i tc -b rules_$i.txt & done wait Each of rules_$i.txt files above includes 100000 tc filter rules to a mlx5 driver NIC ens1f0np0. Without this patch: # time sh insert_tc_rules.sh real 0m50.780s user 0m23.556s sys 4m13.032s With this patch: # time sh insert_tc_rules.sh real 0m17.718s user 0m7.807s sys 3m45.050s Fixes: 047f340b36fc ("net: sched: make skip_sw actually skip software") Reported-by: Shuang Li Signed-off-by: Xin Long Acked-by: Marcelo Ricardo Leitner Reviewed-by: Asbjørn Sloth Tønnesen Tested-by: Asbjørn Sloth Tønnesen Signed-off-by: David S. Miller

net_sched: sch_fq: add three drop_reason

2024-12-06T01:39:04Z

Add three new drop_reason, more precise than generic QDISC_DROP: "tc -s qd" show aggregate counters, it might be more useful to use drop_reason infrastructure for bug hunting. 1) SKB_DROP_REASON_FQ_BAND_LIMIT Whenever a packet is added while its band limit is hit. Corresponding value in "tc -s qd" is bandX_drops XXXX 2) SKB_DROP_REASON_FQ_HORIZON_LIMIT Whenever a packet has a timestamp too far in the future. Corresponding value in "tc -s qd" is horizon_drops XXXX 3) SKB_DROP_REASON_FQ_FLOW_LIMIT Whenever a flow has reached its limit. Corresponding value in "tc -s qd" is flows_plimit XXXX Tested: tc qd replace dev eth1 root fq flow_limit 10 limit 100000 perf record -a -e skb:kfree_skb sleep 1; perf script udp_stream 12329 [004] 216.929492: skb:kfree_skb: skbaddr=0xffff888eabe17e00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT udp_stream 12385 [006] 216.929593: skb:kfree_skb: skbaddr=0xffff888ef8827f00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT udp_stream 12389 [005] 216.929871: skb:kfree_skb: skbaddr=0xffff888ecb9ba500 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT udp_stream 12316 [009] 216.930398: skb:kfree_skb: skbaddr=0xffff888eca286b00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT udp_stream 12400 [008] 216.930490: skb:kfree_skb: skbaddr=0xffff888eabf93d00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_FLOW_LIMIT tc qd replace dev eth1 root fq flow_limit 100 limit 10000 perf record -a -e skb:kfree_skb sleep 1; perf script udp_stream 18074 [001] 1058.318040: skb:kfree_skb: skbaddr=0xffffa23c881fc000 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT udp_stream 18126 [005] 1058.320651: skb:kfree_skb: skbaddr=0xffffa23c6aad4000 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT udp_stream 18118 [006] 1058.321065: skb:kfree_skb: skbaddr=0xffffa23df0d48a00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT udp_stream 18074 [001] 1058.321126: skb:kfree_skb: skbaddr=0xffffa23c881ffa00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT udp_stream 15815 [003] 1058.321224: skb:kfree_skb: skbaddr=0xffffa23c9835db00 rx_sk=(nil) protocol=34525 location=__dev_queue_xmit+0x9d9 reason: FQ_BAND_LIMIT tc -s -d qd sh dev eth1 qdisc fq 8023: root refcnt 257 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 weights 589824 196608 65536 quantum 18Kb initial_quantum 92120b low_rate_threshold 550Kbit refill_delay 40ms timer_slack 10us horizon 10s horizon_drop Sent 492439603330 bytes 336953991 pkt (dropped 61724094, overlimits 0 requeues 4463) backlog 14611228b 9995p requeues 4463 flows 2965 (inactive 1151 throttled 0) band0_pkts 0 band1_pkts 9993 band2_pkts 0 gc 6347 highprio 0 fastpath 30 throttled 5 latency 2.32us flows_plimit 7403693 band1_drops 54320401 Signed-off-by: Eric Dumazet Reviewed-by: Victor Nogueira Reviewed-by: Toke Høiland-Jørgensen Acked-by: Jamal Hadi Salim Link: https://patch.msgid.link/20241204171950.89829-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net/sched: accept TCA_STAB only for root qdisc

2024-10-08T22:38:56Z

Most qdiscs maintain their backlog using qdisc_pkt_len(skb) on the assumption it is invariant between the enqueue() and dequeue() handlers. Unfortunately syzbot can crash a host rather easily using a TBF + SFQ combination, with an STAB on SFQ [1] We can't support TCA_STAB on arbitrary level, this would require to maintain per-qdisc storage. [1] [ 88.796496] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 88.798611] #PF: supervisor read access in kernel mode [ 88.799014] #PF: error_code(0x0000) - not-present page [ 88.799506] PGD 0 P4D 0 [ 88.799829] Oops: Oops: 0000 [#1] SMP NOPTI [ 88.800569] CPU: 14 UID: 0 PID: 2053 Comm: b371744477 Not tainted 6.12.0-rc1-virtme #1117 [ 88.801107] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 88.801779] RIP: 0010:sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq [ 88.802544] Code: 0f b7 50 12 48 8d 04 d5 00 00 00 00 48 89 d6 48 29 d0 48 8b 91 c0 01 00 00 48 c1 e0 03 48 01 c2 66 83 7a 1a 00 7e c0 48 8b 3a <4c> 8b 07 4c 89 02 49 89 50 08 48 c7 47 08 00 00 00 00 48 c7 07 00 All code ======== 0: 0f b7 50 12 movzwl 0x12(%rax),%edx 4: 48 8d 04 d5 00 00 00 lea 0x0(,%rdx,8),%rax b: 00 c: 48 89 d6 mov %rdx,%rsi f: 48 29 d0 sub %rdx,%rax 12: 48 8b 91 c0 01 00 00 mov 0x1c0(%rcx),%rdx 19: 48 c1 e0 03 shl $0x3,%rax 1d: 48 01 c2 add %rax,%rdx 20: 66 83 7a 1a 00 cmpw $0x0,0x1a(%rdx) 25: 7e c0 jle 0xffffffffffffffe7 27: 48 8b 3a mov (%rdx),%rdi 2a:* 4c 8b 07 mov (%rdi),%r8 <-- trapping instruction 2d: 4c 89 02 mov %r8,(%rdx) 30: 49 89 50 08 mov %rdx,0x8(%r8) 34: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi) 3b: 00 3c: 48 rex.W 3d: c7 .byte 0xc7 3e: 07 (bad) ... Code starting with the faulting instruction =========================================== 0: 4c 8b 07 mov (%rdi),%r8 3: 4c 89 02 mov %r8,(%rdx) 6: 49 89 50 08 mov %rdx,0x8(%r8) a: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi) 11: 00 12: 48 rex.W 13: c7 .byte 0xc7 14: 07 (bad) ... [ 88.803721] RSP: 0018:ffff9a1f892b7d58 EFLAGS: 00000206 [ 88.804032] RAX: 0000000000000000 RBX: ffff9a1f8420c800 RCX: ffff9a1f8420c800 [ 88.804560] RDX: ffff9a1f81bc1440 RSI: 0000000000000000 RDI: 0000000000000000 [ 88.805056] RBP: ffffffffc04bb0e0 R08: 0000000000000001 R09: 00000000ff7f9a1f [ 88.805473] R10: 000000000001001b R11: 0000000000009a1f R12: 0000000000000140 [ 88.806194] R13: 0000000000000001 R14: ffff9a1f886df400 R15: ffff9a1f886df4ac [ 88.806734] FS: 00007f445601a740(0000) GS:ffff9a2e7fd80000(0000) knlGS:0000000000000000 [ 88.807225] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 88.807672] CR2: 0000000000000000 CR3: 000000050cc46000 CR4: 00000000000006f0 [ 88.808165] Call Trace: [ 88.808459] [ 88.808710] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434) [ 88.809261] ? page_fault_oops (arch/x86/mm/fault.c:715) [ 88.809561] ? exc_page_fault (./arch/x86/include/asm/irqflags.h:26 ./arch/x86/include/asm/irqflags.h:87 ./arch/x86/include/asm/irqflags.h:147 arch/x86/mm/fault.c:1489 arch/x86/mm/fault.c:1539) [ 88.809806] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) [ 88.810074] ? sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq [ 88.810411] sfq_reset (net/sched/sch_sfq.c:525) sch_sfq [ 88.810671] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036) [ 88.810950] tbf_reset (./include/linux/timekeeping.h:169 net/sched/sch_tbf.c:334) sch_tbf [ 88.811208] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036) [ 88.811484] netif_set_real_num_tx_queues (./include/linux/spinlock.h:396 ./include/net/sch_generic.h:768 net/core/dev.c:2958) [ 88.811870] __tun_detach (drivers/net/tun.c:590 drivers/net/tun.c:673) [ 88.812271] tun_chr_close (drivers/net/tun.c:702 drivers/net/tun.c:3517) [ 88.812505] __fput (fs/file_table.c:432 (discriminator 1)) [ 88.812735] task_work_run (kernel/task_work.c:230) [ 88.813016] do_exit (kernel/exit.c:940) [ 88.813372] ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:58 (discriminator 4)) [ 88.813639] ? handle_mm_fault (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/memcontrol.h:1022 ./include/linux/memcontrol.h:1045 ./include/linux/memcontrol.h:1052 mm/memory.c:5928 mm/memory.c:6088) [ 88.813867] do_group_exit (kernel/exit.c:1070) [ 88.814138] __x64_sys_exit_group (kernel/exit.c:1099) [ 88.814490] x64_sys_call (??:?) [ 88.814791] do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1)) [ 88.815012] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) [ 88.815495] RIP: 0033:0x7f44560f1975 Fixes: 175f9c1bba9b ("net_sched: Add size table for qdiscs") Reported-by: syzbot Signed-off-by: Eric Dumazet Cc: Daniel Borkmann Link: https://patch.msgid.link/20241007184130.3960565-1-edumazet@google.com Signed-off-by: Jakub Kicinski

net/sched: fix false lockdep warning on qdisc root lock

2024-04-26T08:46:41Z

Xiumei and Christoph reported the following lockdep splat, complaining of the qdisc root lock being taken twice: ============================================ WARNING: possible recursive locking detected 6.7.0-rc3+ #598 Not tainted -------------------------------------------- swapper/2/0 is trying to acquire lock: ffff888177190110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70 but task is already holding lock: ffff88811995a110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&sch->q.lock); lock(&sch->q.lock); *** DEADLOCK *** May be due to missing lock nesting notation 5 locks held by swapper/2/0: #0: ffff888135a09d98 ((&in_dev->mr_ifc_timer)){+.-.}-{0:0}, at: call_timer_fn+0x11a/0x510 #1: ffffffffaaee5260 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x2c0/0x1ed0 #2: ffffffffaaee5200 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x209/0x2e70 #3: ffff88811995a110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70 #4: ffffffffaaee5200 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x209/0x2e70 stack backtrace: CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.7.0-rc3+ #598 Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7353+9de0a3cc 04/01/2014 Call Trace: dump_stack_lvl+0x4a/0x80 __lock_acquire+0xfdd/0x3150 lock_acquire+0x1ca/0x540 _raw_spin_lock+0x34/0x80 __dev_queue_xmit+0x1560/0x2e70 tcf_mirred_act+0x82e/0x1260 [act_mirred] tcf_action_exec+0x161/0x480 tcf_classify+0x689/0x1170 prio_enqueue+0x316/0x660 [sch_prio] dev_qdisc_enqueue+0x46/0x220 __dev_queue_xmit+0x1615/0x2e70 ip_finish_output2+0x1218/0x1ed0 __ip_finish_output+0x8b3/0x1350 ip_output+0x163/0x4e0 igmp_ifc_timer_expire+0x44b/0x930 call_timer_fn+0x1a2/0x510 run_timer_softirq+0x54d/0x11a0 __do_softirq+0x1b3/0x88f irq_exit_rcu+0x18f/0x1e0 sysvec_apic_timer_interrupt+0x6f/0x90 This happens when TC does a mirred egress redirect from the root qdisc of device A to the root qdisc of device B. As long as these two locks aren't protecting the same qdisc, they can be acquired in chain: add a per-qdisc lockdep key to silence false warnings. This dynamic key should safely replace the static key we have in sch_htb: it was added to allow enqueueing to the device "direct qdisc" while still holding the qdisc root lock. v2: don't use static keys anymore in HTB direct qdiscs (thanks Eric Dumazet) CC: Maxim Mikityanskiy CC: Xiumei Mu Reported-by: Christoph Paasch Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/451 Signed-off-by: Davide Caratti Link: https://lore.kernel.org/r/7dc06d6158f72053cf877a82e2a7a5bd23692faa.1713448007.git.dcaratti@redhat.com Signed-off-by: Paolo Abeni