Whenever dualpi2 drops packets during peek, it calls qdisc_tree_reduce_backlog. An issue arises because it calls qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops to zero, but peek returns an skb, the parent's qlen_notify callback will be executed even though dualpi2 still has 1 packet on the queue and, thus, mistakenly deactivates the parent's class which leads to a null-ptr-deref: [ 101.427314][ T599] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] SMP KASAN NOPTI [ 101.427755][ T599] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f] [ 101.428048][ T599] CPU: 2 UID: 0 PID: 599 Comm: ping Not tainted 7.1.0-rc5-00284-gbce53c430ed7 #102 PREEMPT(full) [ 101.428400][ T599] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 101.428608][ T599] RIP: 0010:qfq_dequeue (net/sched/sch_qfq.c:1150) sch_qfq [ 101.428821][ T599] Code: 00 fc ff df 80 3c 02 00 0f 85 46 0c 00 00 4c 8d 73 48 48 89 9d b8 02 00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <80> 3c 02 00 0f 85 2d 0c 00 00 48 b8 00 00 00 00 00 fc ff df 4c 8b All code [ 101.429348][ T599] RSP: 0018:ffff8881110df4f0 EFLAGS: 00010216 [ 101.429541][ T599] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: dffffc0000000000 [ 101.429763][ T599] RDX: 0000000000000009 RSI: 00000024c0000000 RDI: ffff88811436c2b0 [ 101.429985][ T599] RBP: ffff88811436c000 R08: ffff88811436c280 R09: 1ffff11021277523 [ 101.430206][ T599] R10: 1ffff11021277526 R11: 1ffff11021277527 R12: 00000024c0000000 [ 101.430423][ T599] R13: ffff88811436c2b8 R14: 0000000000000048 R15: 0000000020000000 [ 101.430642][ T599] FS: 00007f61813e1c40(0000) GS:ffff8881691ef000(0000) knlGS:0000000000000000 [ 101.430913][ T599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 101.431100][ T599] CR2: 00005651650850a8 CR3: 000000010ca0b000 CR4: 0000000000750ef0 [ 101.431320][ T599] PKRU: 55555554 [ 101.431433][ T599] Call Trace: [ 101.431544][ T599] [ 101.431628][ T599] __qdisc_run (net/sched/sch_generic.c:322 net/sched/sch_generic.c:427 net/sched/sch_generic.c:445) [ 101.431792][ T599] ? dev_qdisc_enqueue (./include/trace/events/qdisc.h:49 (discriminator 22) net/core/dev.c:4176 (discriminator 22)) [ 101.431941][ T599] __dev_queue_xmit (./include/net/pkt_sched.h:120 ./include/net/pkt_sched.h:117 net/core/dev.c:4292 net/core/dev.c:4831) Fix this by only calling qdisc_tree_reduce_backlog in peek after the qlen is restored. Fixes: 8f9516daedd6 ("sched: Add enqueue/dequeue of dualpi2 qdisc") Acked-by: Jamal Hadi Salim Signed-off-by: Victor Nogueira --- net/sched/sch_dualpi2.c | 41 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 39 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_dualpi2.c b/net/sched/sch_dualpi2.c index a22489c14458..05285775b454 100644 --- a/net/sched/sch_dualpi2.c +++ b/net/sched/sch_dualpi2.c @@ -579,7 +579,7 @@ static void drop_and_retry(struct dualpi2_sched_data *q, struct sk_buff *skb, qdisc_qstats_drop(sch); } -static struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch) +static struct sk_buff *__dualpi2_qdisc_dequeue(struct Qdisc *sch) { struct dualpi2_sched_data *q = qdisc_priv(sch); struct sk_buff *skb; @@ -605,12 +605,49 @@ static struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch) break; } + return skb; +} + +static void dualpi2_dequeue_drop(struct Qdisc *sch) +{ + struct dualpi2_sched_data *q = qdisc_priv(sch); + if (q->deferred_drops_cnt) { qdisc_tree_reduce_backlog(sch, q->deferred_drops_cnt, q->deferred_drops_len); q->deferred_drops_cnt = 0; q->deferred_drops_len = 0; } +} + +static struct sk_buff *dualpi2_qdisc_dequeue(struct Qdisc *sch) +{ + struct sk_buff *skb; + + skb = __dualpi2_qdisc_dequeue(sch); + + dualpi2_dequeue_drop(sch); + + return skb; +} + +static struct sk_buff *dualpi2_peek(struct Qdisc *sch) +{ + struct sk_buff *skb = skb_peek(&sch->gso_skb); + + if (!skb) { + skb = __dualpi2_qdisc_dequeue(sch); + + if (skb) { + __skb_queue_head(&sch->gso_skb, skb); + /* it's still part of the queue */ + qdisc_qstats_backlog_inc(sch, skb); + sch->q.qlen++; + } + + dualpi2_dequeue_drop(sch); + } + return skb; } @@ -1165,7 +1202,7 @@ static struct Qdisc_ops dualpi2_qdisc_ops __read_mostly = { .priv_size = sizeof(struct dualpi2_sched_data), .enqueue = dualpi2_qdisc_enqueue, .dequeue = dualpi2_qdisc_dequeue, - .peek = qdisc_peek_dequeued, + .peek = dualpi2_peek, .init = dualpi2_init, .destroy = dualpi2_destroy, .reset = dualpi2_reset, -- 2.54.0