| Message ID | 20220930223042.351022-1-vinicius.gomes@intel.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net,v1] net/sched: taprio: Fix crash when adding child qdisc | expand |
On Fri, Sep 30, 2022 at 03:30:42PM -0700, Vinicius Costa Gomes wrote: > It was reported by Husaini that since commit 1461d212ab27 ("net/sched: > taprio: make qdisc_leaf() see the per-netdev-queue pfifo child > qdiscs"), there was a NULL dereference when adding a child qdisc (ETF > in this case) when using taprio full offload. > > The issue seems to be that since commit 13511704f8d7 ("net: taprio > offload: enforce qdisc to netdev queue mapping"), the array of child > qdiscs (q->qdiscs[]) was not used, and even free'd when full offload > mode is used, in attach(). > > The current implementation since 1461d212ab27 (which I feel is a > sensible change) requires that the q->qdiscs[] array is always valid. > The fix is to not deallocate it, and keep it having references to each > child qdisc. > > Log: > > [ 2295.318620] IPv6: ADDRCONF(NETDEV_CHANGE): enp170s0: link becomes ready > [ 2371.758745] BUG: kernel NULL pointer dereference, address: 0000000000000008 > [ 2371.765697] #PF: supervisor read access in kernel mode > [ 2371.770825] #PF: error_code(0x0000) - not-present page > [ 2371.775952] PGD 0 P4D 0 > [ 2371.778494] Oops: 0000 [#1] PREEMPT SMP NOPTI > [ 2371.782844] CPU: 0 PID: 17964 Comm: tc Tainted: G U W 6.0.0-rc6-intel-ese-standard-lts+ #95 > [ 2371.792374] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U DDR4 SODIMM RVP, BIOS TGLIFUI1.R00.4204.A00.2105270302 05/27/2021 > [ 2371.805701] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] > [ 2371.811011] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. > [ 2371.817867] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 > [ 2371.823078] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 > [ 2371.830190] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 > [ 2371.837307] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 > [ 2371.844420] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 > [ 2371.851534] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 > [ 2371.858646] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 > [ 2371.866707] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 2371.872435] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 > [ 2371.879546] PKRU: 55555554 > [ 2371.882261] Call Trace: > [ 2371.884719] <TASK> > [ 2371.886831] tc_modify_qdisc+0x75/0x7c0 > [ 2371.890667] rtnetlink_rcv_msg+0x141/0x3c0 > [ 2371.894764] ? _copy_to_iter+0x1b0/0x5a0 > [ 2371.898685] ? rtnl_calcit.isra.0+0x140/0x140 > [ 2371.903040] netlink_rcv_skb+0x4e/0x100 > [ 2371.906878] netlink_unicast+0x197/0x240 > [ 2371.910797] netlink_sendmsg+0x246/0x4a0 > [ 2371.914718] sock_sendmsg+0x5f/0x70 > [ 2371.918207] ____sys_sendmsg+0x20f/0x280 > [ 2371.922130] ? copy_msghdr_from_user+0x72/0xb0 > [ 2371.926570] ___sys_sendmsg+0x7c/0xc0 > [ 2371.930233] ? ___sys_recvmsg+0x89/0xc0 > [ 2371.934070] __sys_sendmsg+0x59/0xa0 > [ 2371.937647] do_syscall_64+0x40/0x90 > [ 2371.941224] entry_SYSCALL_64_after_hwframe+0x63/0xcd > [ 2371.946273] RIP: 0033:0x7fd2fc38e707 > [ 2371.949847] Code: 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 > [ 2371.968521] RSP: 002b:00007fffafdf9ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e > [ 2371.976070] RAX: ffffffffffffffda RBX: 0000000063359bf0 RCX: 00007fd2fc38e707 > [ 2371.983183] RDX: 0000000000000000 RSI: 00007fffafdf9d50 RDI: 0000000000000003 > [ 2371.990293] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 > [ 2371.997406] R10: 00007fd2fc28d670 R11: 0000000000000246 R12: 0000000000000001 > [ 2372.004520] R13: 00005583e730c476 R14: 00005583e730c48a R15: 00005583e7333280 > [ 2372.011637] </TASK> > [ 2372.013830] Modules linked in: sch_taprio bnep 8021q bluetooth ecdh_generic ecc ecryptfs nfsd sch_fq_codel uio uhid iwlwifi cfg80211 i915 x86_pkg_temp_thermal kvm_intel kvm hid_sensor_als hid_sensor_incl_3d hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_magn_3d hid_sensor_trigger hid_sensor_iio_common hid_sensor_custom hid_sensor_hub atkbd mei_hdcp intel_ishtp_hid libps2 mei_wdt vivaldi_fmap dwc3 dwmac_intel stmmac e1000e ax88179_178a usbnet mii mei_me igc thunderbolt udc_core mei pcs_xpcs wdat_wdt irqbypass spi_pxa2xx_platform phylink intel_ish_ipc i2c_i801 dw_dmac tpm_crb intel_rapl_msr pcspkr dw_dmac_core i2c_smbus intel_ishtp tpm_tis parport_pc intel_pmc_core igen6_edac tpm_tis_core thermal parport i8042 tpm edac_core dwc3_pci video drm_buddy ttm drm_display_helper fuse configfs snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_pcm snd_timer snd soundcore > [ 2372.092427] CR2: 0000000000000008 > [ 2372.095744] ---[ end trace 0000000000000000 ]--- > [ 2372.276814] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] > [ 2372.282140] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. > [ 2372.288995] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 > [ 2372.294215] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 > [ 2372.301329] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 > [ 2372.308442] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 > [ 2372.315550] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 > [ 2372.322663] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 > [ 2372.329774] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 > [ 2372.337840] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 2372.343569] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 > [ 2372.350680] PKRU: 55555554 > > Fixes: 1461d212ab27 ("net/sched: taprio: make qdisc_leaf() see the per-netdev-queue pfifo child qdiscs") > Reported-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com> > Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com> > --- > This patch is more to make others aware of this issue and to explain > what I think is going on. Perhaps the correct solution is something > else. (and that explicit refcount seems wrong, but getting warnings > without it). > > I am questioning my sanity, I have clear memories about testing the > commit above and it working fine. > > Reverting commit 1461d212ab27 is another alternative, but I think it's > worth to keep that and fix the problem that it exposed. > > > net/sched/sch_taprio.c | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c > index 86675a79da1e..75aacfff2d5e 100644 > --- a/net/sched/sch_taprio.c > +++ b/net/sched/sch_taprio.c > @@ -1763,12 +1763,6 @@ static void taprio_attach(struct Qdisc *sch) > if (old) > qdisc_put(old); > } > - > - /* access to the child qdiscs is not needed in offload mode */ > - if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { > - kfree(q->qdiscs); > - q->qdiscs = NULL; > - } > } omfg, I didn't include this hunk in the patch? yikes, sorry. > > static struct netdev_queue *taprio_queue_get(struct Qdisc *sch, > @@ -1801,8 +1795,9 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, > *old = dev_graft_qdisc(dev_queue, new); > } else { > *old = q->qdiscs[cl - 1]; > - q->qdiscs[cl - 1] = new; > } > + q->qdiscs[cl - 1] = new; > + qdisc_refcount_inc(new); What warning are you getting without this part of the change? > > if (new) > new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT; > -- > 2.37.3 >
Vladimir Oltean <vladimir.oltean@nxp.com> writes: > On Fri, Sep 30, 2022 at 03:30:42PM -0700, Vinicius Costa Gomes wrote: >> It was reported by Husaini that since commit 1461d212ab27 ("net/sched: >> taprio: make qdisc_leaf() see the per-netdev-queue pfifo child >> qdiscs"), there was a NULL dereference when adding a child qdisc (ETF >> in this case) when using taprio full offload. >> >> The issue seems to be that since commit 13511704f8d7 ("net: taprio >> offload: enforce qdisc to netdev queue mapping"), the array of child >> qdiscs (q->qdiscs[]) was not used, and even free'd when full offload >> mode is used, in attach(). >> >> The current implementation since 1461d212ab27 (which I feel is a >> sensible change) requires that the q->qdiscs[] array is always valid. >> The fix is to not deallocate it, and keep it having references to each >> child qdisc. >> >> Log: >> >> [ 2295.318620] IPv6: ADDRCONF(NETDEV_CHANGE): enp170s0: link becomes ready >> [ 2371.758745] BUG: kernel NULL pointer dereference, address: 0000000000000008 >> [ 2371.765697] #PF: supervisor read access in kernel mode >> [ 2371.770825] #PF: error_code(0x0000) - not-present page >> [ 2371.775952] PGD 0 P4D 0 >> [ 2371.778494] Oops: 0000 [#1] PREEMPT SMP NOPTI >> [ 2371.782844] CPU: 0 PID: 17964 Comm: tc Tainted: G U W 6.0.0-rc6-intel-ese-standard-lts+ #95 >> [ 2371.792374] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U DDR4 SODIMM RVP, BIOS TGLIFUI1.R00.4204.A00.2105270302 05/27/2021 >> [ 2371.805701] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] >> [ 2371.811011] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. >> [ 2371.817867] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 >> [ 2371.823078] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 >> [ 2371.830190] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 >> [ 2371.837307] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 >> [ 2371.844420] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 >> [ 2371.851534] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 >> [ 2371.858646] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 >> [ 2371.866707] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 2371.872435] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 >> [ 2371.879546] PKRU: 55555554 >> [ 2371.882261] Call Trace: >> [ 2371.884719] <TASK> >> [ 2371.886831] tc_modify_qdisc+0x75/0x7c0 >> [ 2371.890667] rtnetlink_rcv_msg+0x141/0x3c0 >> [ 2371.894764] ? _copy_to_iter+0x1b0/0x5a0 >> [ 2371.898685] ? rtnl_calcit.isra.0+0x140/0x140 >> [ 2371.903040] netlink_rcv_skb+0x4e/0x100 >> [ 2371.906878] netlink_unicast+0x197/0x240 >> [ 2371.910797] netlink_sendmsg+0x246/0x4a0 >> [ 2371.914718] sock_sendmsg+0x5f/0x70 >> [ 2371.918207] ____sys_sendmsg+0x20f/0x280 >> [ 2371.922130] ? copy_msghdr_from_user+0x72/0xb0 >> [ 2371.926570] ___sys_sendmsg+0x7c/0xc0 >> [ 2371.930233] ? ___sys_recvmsg+0x89/0xc0 >> [ 2371.934070] __sys_sendmsg+0x59/0xa0 >> [ 2371.937647] do_syscall_64+0x40/0x90 >> [ 2371.941224] entry_SYSCALL_64_after_hwframe+0x63/0xcd >> [ 2371.946273] RIP: 0033:0x7fd2fc38e707 >> [ 2371.949847] Code: 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 >> [ 2371.968521] RSP: 002b:00007fffafdf9ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e >> [ 2371.976070] RAX: ffffffffffffffda RBX: 0000000063359bf0 RCX: 00007fd2fc38e707 >> [ 2371.983183] RDX: 0000000000000000 RSI: 00007fffafdf9d50 RDI: 0000000000000003 >> [ 2371.990293] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 >> [ 2371.997406] R10: 00007fd2fc28d670 R11: 0000000000000246 R12: 0000000000000001 >> [ 2372.004520] R13: 00005583e730c476 R14: 00005583e730c48a R15: 00005583e7333280 >> [ 2372.011637] </TASK> >> [ 2372.013830] Modules linked in: sch_taprio bnep 8021q bluetooth ecdh_generic ecc ecryptfs nfsd sch_fq_codel uio uhid iwlwifi cfg80211 i915 x86_pkg_temp_thermal kvm_intel kvm hid_sensor_als hid_sensor_incl_3d hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_magn_3d hid_sensor_trigger hid_sensor_iio_common hid_sensor_custom hid_sensor_hub atkbd mei_hdcp intel_ishtp_hid libps2 mei_wdt vivaldi_fmap dwc3 dwmac_intel stmmac e1000e ax88179_178a usbnet mii mei_me igc thunderbolt udc_core mei pcs_xpcs wdat_wdt irqbypass spi_pxa2xx_platform phylink intel_ish_ipc i2c_i801 dw_dmac tpm_crb intel_rapl_msr pcspkr dw_dmac_core i2c_smbus intel_ishtp tpm_tis parport_pc intel_pmc_core igen6_edac tpm_tis_core thermal parport i8042 tpm edac_core dwc3_pci video drm_buddy ttm drm_display_helper fuse configfs snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_pcm snd_timer snd soundcore >> [ 2372.092427] CR2: 0000000000000008 >> [ 2372.095744] ---[ end trace 0000000000000000 ]--- >> [ 2372.276814] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] >> [ 2372.282140] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. >> [ 2372.288995] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 >> [ 2372.294215] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 >> [ 2372.301329] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 >> [ 2372.308442] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 >> [ 2372.315550] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 >> [ 2372.322663] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 >> [ 2372.329774] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 >> [ 2372.337840] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 2372.343569] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 >> [ 2372.350680] PKRU: 55555554 >> >> Fixes: 1461d212ab27 ("net/sched: taprio: make qdisc_leaf() see the per-netdev-queue pfifo child qdiscs") >> Reported-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com> >> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com> >> --- >> This patch is more to make others aware of this issue and to explain >> what I think is going on. Perhaps the correct solution is something >> else. (and that explicit refcount seems wrong, but getting warnings >> without it). >> >> I am questioning my sanity, I have clear memories about testing the >> commit above and it working fine. >> >> Reverting commit 1461d212ab27 is another alternative, but I think it's >> worth to keep that and fix the problem that it exposed. >> >> >> net/sched/sch_taprio.c | 9 ++------- >> 1 file changed, 2 insertions(+), 7 deletions(-) >> >> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c >> index 86675a79da1e..75aacfff2d5e 100644 >> --- a/net/sched/sch_taprio.c >> +++ b/net/sched/sch_taprio.c >> @@ -1763,12 +1763,6 @@ static void taprio_attach(struct Qdisc *sch) >> if (old) >> qdisc_put(old); >> } >> - >> - /* access to the child qdiscs is not needed in offload mode */ >> - if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { >> - kfree(q->qdiscs); >> - q->qdiscs = NULL; >> - } >> } > > omfg, I didn't include this hunk in the patch? yikes, sorry. > >> >> static struct netdev_queue *taprio_queue_get(struct Qdisc *sch, >> @@ -1801,8 +1795,9 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, >> *old = dev_graft_qdisc(dev_queue, new); >> } else { >> *old = q->qdiscs[cl - 1]; >> - q->qdiscs[cl - 1] = new; >> } >> + q->qdiscs[cl - 1] = new; >> + qdisc_refcount_inc(new); > > What warning are you getting without this part of the change? Something like this: [ 73.174189] refcount_t: underflow; use-after-free. [ 73.174197] WARNING: CPU: 10 PID: 878 at lib/refcount.c:28 refcount_warn_saturate+0xd8/0xe0 [ 73.174204] Modules linked in: sch_taprio(E) snd_hda_codec_hdmi(E) snd_hda_codec_realtek(E) snd_hda_codec_generic(E) ledtrig_audio(E) snd_hda_intel(E) snd_intel_dspcfg(E) snd_hda_codec(E) snd_hda_core(E) snd_pcm(E) igc(E) snd_timer(E) intel_pch_thermal(E) joydev(E) usbhid(E) efivarfs(E) [ 73.174226] CPU: 10 PID: 878 Comm: tc Tainted: G E 6.0.0-rc7+ #13 [ 73.174229] Hardware name: Gigabyte Technology Co., Ltd. Z390 AORUS ULTRA/Z390 AORUS ULTRA-CF, BIOS F7 03/14/2019 [ 73.174232] RIP: 0010:refcount_warn_saturate+0xd8/0xe0 [ 73.174246] Code: ff 48 c7 c7 58 4d 61 a4 c6 05 39 59 ac 01 01 e8 36 92 71 00 0f 0b c3 48 c7 c7 00 4d 61 a4 c6 05 25 59 ac 01 01 e8 20 92 71 00 <0f> 0b c3 0f 1f 44 00 00 8b 07 3d 00 00 00 c0 74 12 83 f8 01 74 13 [ 73.174250] RSP: 0018:ffffa24c8336b9b8 EFLAGS: 00010296 [ 73.174254] RAX: 0000000000000026 RBX: 0000000000000001 RCX: 0000000000000027 [ 73.174257] RDX: ffff9ebfae49c868 RSI: 0000000000000001 RDI: ffff9ebfae49c860 [ 73.174260] RBP: ffff9ebc0a4eb000 R08: 0000000000000000 R09: ffffffffa4e72f40 [ 73.174262] R10: ffffa24c8336b870 R11: ffffffffa4ee2f88 R12: ffff9ebc10bfc000 [ 73.174265] R13: 0000000000000000 R14: ffff9ebc0a4eb000 R15: 0000000000000000 [ 73.174268] FS: 00007f4b546f5c40(0000) GS:ffff9ebfae480000(0000) knlGS:0000000000000000 [ 73.174271] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 73.174273] CR2: 00005587d1ad02c1 CR3: 0000000128460005 CR4: 00000000003706e0 [ 73.174276] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 73.174278] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 73.174281] Call Trace: [ 73.174284] <TASK> [ 73.174287] taprio_destroy+0xa4/0x110 [sch_taprio] [ 73.174295] qdisc_destroy+0x48/0x180 [ 73.174300] qdisc_graft+0x573/0x6b0 [ 73.174308] tc_get_qdisc+0x157/0x3d0 [ 73.174323] rtnetlink_rcv_msg+0x155/0x520 [ 73.174328] ? netlink_deliver_tap+0x78/0x3f0 [ 73.174334] ? rtnl_getlink+0x3d0/0x3d0 [ 73.174339] netlink_rcv_skb+0x4e/0xf0 [ 73.174348] netlink_unicast+0x15e/0x230 [ 73.174354] netlink_sendmsg+0x234/0x490 [ 73.174363] sock_sendmsg+0x30/0x40 [ 73.174368] ____sys_sendmsg+0x214/0x230 [ 73.174373] ? import_iovec+0x17/0x20 [ 73.174377] ? copy_msghdr_from_user+0x5d/0x80 [ 73.174384] ___sys_sendmsg+0x86/0xd0 [ 73.174400] ? lock_is_held_type+0x9b/0x100 [ 73.174405] ? find_held_lock+0x2b/0x80 [ 73.174413] __sys_sendmsg+0x47/0x80 [ 73.174423] do_syscall_64+0x34/0x80 [ 73.174428] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 73.174432] RIP: 0033:0x7f4b54817ab7 [ 73.174435] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 f3 0f 1e fa 80 3d 2d 9b 0d 00 00 74 13 b8 2e 00 00 00 c5 fc 77 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 [ 73.174438] RSP: 002b:00007fff996ecf18 EFLAGS: 00000202 ORIG_RAX: 000000000000002e [ 73.174442] RAX: ffffffffffffffda RBX: 00005587d1af6f60 RCX: 00007f4b54817ab7 [ 73.174444] RDX: 0000000000000000 RSI: 00007fff996ecf68 RDI: 0000000000000003 [ 73.174447] RBP: 00000000633b1a29 R08: 0000000000000001 R09: 00007fff996ecc98 [ 73.174450] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000 [ 73.174452] R13: 00007fff996ed060 R14: 0000000000000001 R15: 00005587d1ad219a [ 73.174464] </TASK> [ 73.174466] irq event stamp: 7453 [ 73.174468] hardirqs last enabled at (7461): [<ffffffffa30fa962>] __up_console_sem+0x52/0x60 [ 73.174473] hardirqs last disabled at (7468): [<ffffffffa30fa947>] __up_console_sem+0x37/0x60 [ 73.174476] softirqs last enabled at (7094): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 [ 73.174481] softirqs last disabled at (7089): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 [ 73.174484] ---[ end trace 0000000000000000 ]---
On Mon, Oct 03, 2022 at 10:25:03AM -0700, Vinicius Costa Gomes wrote: > Something like this: > > [ 73.174189] refcount_t: underflow; use-after-free. > [ 73.174197] WARNING: CPU: 10 PID: 878 at lib/refcount.c:28 refcount_warn_saturate+0xd8/0xe0 > [ 73.174204] Modules linked in: sch_taprio(E) snd_hda_codec_hdmi(E) snd_hda_codec_realtek(E) snd_hda_codec_generic(E) ledtrig_audio(E) snd_hda_intel(E) snd_intel_dspcfg(E) snd_hda_codec(E) snd_hda_core(E) snd_pcm(E) igc(E) snd_timer(E) intel_pch_thermal(E) joydev(E) usbhid(E) efivarfs(E) > [ 73.174226] CPU: 10 PID: 878 Comm: tc Tainted: G E 6.0.0-rc7+ #13 > [ 73.174229] Hardware name: Gigabyte Technology Co., Ltd. Z390 AORUS ULTRA/Z390 AORUS ULTRA-CF, BIOS F7 03/14/2019 > [ 73.174232] RIP: 0010:refcount_warn_saturate+0xd8/0xe0 > [ 73.174246] Code: ff 48 c7 c7 58 4d 61 a4 c6 05 39 59 ac 01 01 e8 36 92 71 00 0f 0b c3 48 c7 c7 00 4d 61 a4 c6 05 25 59 ac 01 01 e8 20 92 71 00 <0f> 0b c3 0f 1f 44 00 00 8b 07 3d 00 00 00 c0 74 12 83 f8 01 74 13 > [ 73.174250] RSP: 0018:ffffa24c8336b9b8 EFLAGS: 00010296 > [ 73.174254] RAX: 0000000000000026 RBX: 0000000000000001 RCX: 0000000000000027 > [ 73.174257] RDX: ffff9ebfae49c868 RSI: 0000000000000001 RDI: ffff9ebfae49c860 > [ 73.174260] RBP: ffff9ebc0a4eb000 R08: 0000000000000000 R09: ffffffffa4e72f40 > [ 73.174262] R10: ffffa24c8336b870 R11: ffffffffa4ee2f88 R12: ffff9ebc10bfc000 > [ 73.174265] R13: 0000000000000000 R14: ffff9ebc0a4eb000 R15: 0000000000000000 > [ 73.174268] FS: 00007f4b546f5c40(0000) GS:ffff9ebfae480000(0000) knlGS:0000000000000000 > [ 73.174271] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 73.174273] CR2: 00005587d1ad02c1 CR3: 0000000128460005 CR4: 00000000003706e0 > [ 73.174276] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 73.174278] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 73.174281] Call Trace: > [ 73.174284] <TASK> > [ 73.174287] taprio_destroy+0xa4/0x110 [sch_taprio] > [ 73.174295] qdisc_destroy+0x48/0x180 > [ 73.174300] qdisc_graft+0x573/0x6b0 > [ 73.174308] tc_get_qdisc+0x157/0x3d0 > [ 73.174323] rtnetlink_rcv_msg+0x155/0x520 > [ 73.174328] ? netlink_deliver_tap+0x78/0x3f0 > [ 73.174334] ? rtnl_getlink+0x3d0/0x3d0 > [ 73.174339] netlink_rcv_skb+0x4e/0xf0 > [ 73.174348] netlink_unicast+0x15e/0x230 > [ 73.174354] netlink_sendmsg+0x234/0x490 > [ 73.174363] sock_sendmsg+0x30/0x40 > [ 73.174368] ____sys_sendmsg+0x214/0x230 > [ 73.174373] ? import_iovec+0x17/0x20 > [ 73.174377] ? copy_msghdr_from_user+0x5d/0x80 > [ 73.174384] ___sys_sendmsg+0x86/0xd0 > [ 73.174400] ? lock_is_held_type+0x9b/0x100 > [ 73.174405] ? find_held_lock+0x2b/0x80 > [ 73.174413] __sys_sendmsg+0x47/0x80 > [ 73.174423] do_syscall_64+0x34/0x80 > [ 73.174428] entry_SYSCALL_64_after_hwframe+0x63/0xcd > [ 73.174432] RIP: 0033:0x7f4b54817ab7 > [ 73.174435] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 f3 0f 1e fa 80 3d 2d 9b 0d 00 00 74 13 b8 2e 00 00 00 c5 fc 77 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 > [ 73.174438] RSP: 002b:00007fff996ecf18 EFLAGS: 00000202 ORIG_RAX: 000000000000002e > [ 73.174442] RAX: ffffffffffffffda RBX: 00005587d1af6f60 RCX: 00007f4b54817ab7 > [ 73.174444] RDX: 0000000000000000 RSI: 00007fff996ecf68 RDI: 0000000000000003 > [ 73.174447] RBP: 00000000633b1a29 R08: 0000000000000001 R09: 00007fff996ecc98 > [ 73.174450] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000 > [ 73.174452] R13: 00007fff996ed060 R14: 0000000000000001 R15: 00005587d1ad219a > [ 73.174464] </TASK> > [ 73.174466] irq event stamp: 7453 > [ 73.174468] hardirqs last enabled at (7461): [<ffffffffa30fa962>] __up_console_sem+0x52/0x60 > [ 73.174473] hardirqs last disabled at (7468): [<ffffffffa30fa947>] __up_console_sem+0x37/0x60 > [ 73.174476] softirqs last enabled at (7094): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 > [ 73.174481] softirqs last disabled at (7089): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 > [ 73.174484] ---[ end trace 0000000000000000 ]--- I studied the problem a bit and unfortunately your fix is not correct. It is not sufficient to call qdisc_refcount_inc() on the child qdiscs grafted in taprio_graft(), there are still other sources of use-after-free. I will send a revert of my patch soon, and explain there in more detail what the problem is. Sorry for the trouble and thanks for reporting the problem and proposing a solution.
Vladimir Oltean <vladimir.oltean@nxp.com> writes: > On Mon, Oct 03, 2022 at 10:25:03AM -0700, Vinicius Costa Gomes wrote: >> Something like this: >> >> [ 73.174189] refcount_t: underflow; use-after-free. >> [ 73.174197] WARNING: CPU: 10 PID: 878 at lib/refcount.c:28 refcount_warn_saturate+0xd8/0xe0 >> [ 73.174204] Modules linked in: sch_taprio(E) snd_hda_codec_hdmi(E) snd_hda_codec_realtek(E) snd_hda_codec_generic(E) ledtrig_audio(E) snd_hda_intel(E) snd_intel_dspcfg(E) snd_hda_codec(E) snd_hda_core(E) snd_pcm(E) igc(E) snd_timer(E) intel_pch_thermal(E) joydev(E) usbhid(E) efivarfs(E) >> [ 73.174226] CPU: 10 PID: 878 Comm: tc Tainted: G E 6.0.0-rc7+ #13 >> [ 73.174229] Hardware name: Gigabyte Technology Co., Ltd. Z390 AORUS ULTRA/Z390 AORUS ULTRA-CF, BIOS F7 03/14/2019 >> [ 73.174232] RIP: 0010:refcount_warn_saturate+0xd8/0xe0 >> [ 73.174246] Code: ff 48 c7 c7 58 4d 61 a4 c6 05 39 59 ac 01 01 e8 36 92 71 00 0f 0b c3 48 c7 c7 00 4d 61 a4 c6 05 25 59 ac 01 01 e8 20 92 71 00 <0f> 0b c3 0f 1f 44 00 00 8b 07 3d 00 00 00 c0 74 12 83 f8 01 74 13 >> [ 73.174250] RSP: 0018:ffffa24c8336b9b8 EFLAGS: 00010296 >> [ 73.174254] RAX: 0000000000000026 RBX: 0000000000000001 RCX: 0000000000000027 >> [ 73.174257] RDX: ffff9ebfae49c868 RSI: 0000000000000001 RDI: ffff9ebfae49c860 >> [ 73.174260] RBP: ffff9ebc0a4eb000 R08: 0000000000000000 R09: ffffffffa4e72f40 >> [ 73.174262] R10: ffffa24c8336b870 R11: ffffffffa4ee2f88 R12: ffff9ebc10bfc000 >> [ 73.174265] R13: 0000000000000000 R14: ffff9ebc0a4eb000 R15: 0000000000000000 >> [ 73.174268] FS: 00007f4b546f5c40(0000) GS:ffff9ebfae480000(0000) knlGS:0000000000000000 >> [ 73.174271] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 73.174273] CR2: 00005587d1ad02c1 CR3: 0000000128460005 CR4: 00000000003706e0 >> [ 73.174276] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> [ 73.174278] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> [ 73.174281] Call Trace: >> [ 73.174284] <TASK> >> [ 73.174287] taprio_destroy+0xa4/0x110 [sch_taprio] >> [ 73.174295] qdisc_destroy+0x48/0x180 >> [ 73.174300] qdisc_graft+0x573/0x6b0 >> [ 73.174308] tc_get_qdisc+0x157/0x3d0 >> [ 73.174323] rtnetlink_rcv_msg+0x155/0x520 >> [ 73.174328] ? netlink_deliver_tap+0x78/0x3f0 >> [ 73.174334] ? rtnl_getlink+0x3d0/0x3d0 >> [ 73.174339] netlink_rcv_skb+0x4e/0xf0 >> [ 73.174348] netlink_unicast+0x15e/0x230 >> [ 73.174354] netlink_sendmsg+0x234/0x490 >> [ 73.174363] sock_sendmsg+0x30/0x40 >> [ 73.174368] ____sys_sendmsg+0x214/0x230 >> [ 73.174373] ? import_iovec+0x17/0x20 >> [ 73.174377] ? copy_msghdr_from_user+0x5d/0x80 >> [ 73.174384] ___sys_sendmsg+0x86/0xd0 >> [ 73.174400] ? lock_is_held_type+0x9b/0x100 >> [ 73.174405] ? find_held_lock+0x2b/0x80 >> [ 73.174413] __sys_sendmsg+0x47/0x80 >> [ 73.174423] do_syscall_64+0x34/0x80 >> [ 73.174428] entry_SYSCALL_64_after_hwframe+0x63/0xcd >> [ 73.174432] RIP: 0033:0x7f4b54817ab7 >> [ 73.174435] Code: 0d 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb ba 0f 1f 00 f3 0f 1e fa 80 3d 2d 9b 0d 00 00 74 13 b8 2e 00 00 00 c5 fc 77 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 >> [ 73.174438] RSP: 002b:00007fff996ecf18 EFLAGS: 00000202 ORIG_RAX: 000000000000002e >> [ 73.174442] RAX: ffffffffffffffda RBX: 00005587d1af6f60 RCX: 00007f4b54817ab7 >> [ 73.174444] RDX: 0000000000000000 RSI: 00007fff996ecf68 RDI: 0000000000000003 >> [ 73.174447] RBP: 00000000633b1a29 R08: 0000000000000001 R09: 00007fff996ecc98 >> [ 73.174450] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000 >> [ 73.174452] R13: 00007fff996ed060 R14: 0000000000000001 R15: 00005587d1ad219a >> [ 73.174464] </TASK> >> [ 73.174466] irq event stamp: 7453 >> [ 73.174468] hardirqs last enabled at (7461): [<ffffffffa30fa962>] __up_console_sem+0x52/0x60 >> [ 73.174473] hardirqs last disabled at (7468): [<ffffffffa30fa947>] __up_console_sem+0x37/0x60 >> [ 73.174476] softirqs last enabled at (7094): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 >> [ 73.174481] softirqs last disabled at (7089): [<ffffffffa3079d3f>] __irq_exit_rcu+0xbf/0xf0 >> [ 73.174484] ---[ end trace 0000000000000000 ]--- > > I studied the problem a bit and unfortunately your fix is not correct. > It is not sufficient to call qdisc_refcount_inc() on the child qdiscs > grafted in taprio_graft(), there are still other sources of use-after-free. > I was afraid that this this would happen. I need to stop, grab some tea and think very carefully how to simplify the lifetime handling of the children qdiscs. It has become complicated now that the offloaded/not-offloaded modes are very different internally. > I will send a revert of my patch soon, and explain there in more detail > what the problem is. Sorry for the trouble and thanks for reporting the > problem and proposing a solution. Agreed. The revert is safer for net. No worries. Been there, done that. Cheers,
On Tue, Oct 04, 2022 at 03:41:30PM -0700, Vinicius Costa Gomes wrote: > I was afraid that this this would happen. I need to stop, grab some tea > and think very carefully how to simplify the lifetime handling of the > children qdiscs. It has become complicated now that the > offloaded/not-offloaded modes are very different internally. Truth be told, it's not like the problem Yannick described in commit 13511704f8d7 ("net: taprio offload: enforce qdisc to netdev queue mapping") is unique only to the offloaded taprio, but I just don't know enough about qdiscs to see a different design than what is currently implemented.
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c index 86675a79da1e..75aacfff2d5e 100644 --- a/net/sched/sch_taprio.c +++ b/net/sched/sch_taprio.c @@ -1763,12 +1763,6 @@ static void taprio_attach(struct Qdisc *sch) if (old) qdisc_put(old); } - - /* access to the child qdiscs is not needed in offload mode */ - if (FULL_OFFLOAD_IS_ENABLED(q->flags)) { - kfree(q->qdiscs); - q->qdiscs = NULL; - } } static struct netdev_queue *taprio_queue_get(struct Qdisc *sch, @@ -1801,8 +1795,9 @@ static int taprio_graft(struct Qdisc *sch, unsigned long cl, *old = dev_graft_qdisc(dev_queue, new); } else { *old = q->qdiscs[cl - 1]; - q->qdiscs[cl - 1] = new; } + q->qdiscs[cl - 1] = new; + qdisc_refcount_inc(new); if (new) new->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
It was reported by Husaini that since commit 1461d212ab27 ("net/sched: taprio: make qdisc_leaf() see the per-netdev-queue pfifo child qdiscs"), there was a NULL dereference when adding a child qdisc (ETF in this case) when using taprio full offload. The issue seems to be that since commit 13511704f8d7 ("net: taprio offload: enforce qdisc to netdev queue mapping"), the array of child qdiscs (q->qdiscs[]) was not used, and even free'd when full offload mode is used, in attach(). The current implementation since 1461d212ab27 (which I feel is a sensible change) requires that the q->qdiscs[] array is always valid. The fix is to not deallocate it, and keep it having references to each child qdisc. Log: [ 2295.318620] IPv6: ADDRCONF(NETDEV_CHANGE): enp170s0: link becomes ready [ 2371.758745] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 2371.765697] #PF: supervisor read access in kernel mode [ 2371.770825] #PF: error_code(0x0000) - not-present page [ 2371.775952] PGD 0 P4D 0 [ 2371.778494] Oops: 0000 [#1] PREEMPT SMP NOPTI [ 2371.782844] CPU: 0 PID: 17964 Comm: tc Tainted: G U W 6.0.0-rc6-intel-ese-standard-lts+ #95 [ 2371.792374] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U DDR4 SODIMM RVP, BIOS TGLIFUI1.R00.4204.A00.2105270302 05/27/2021 [ 2371.805701] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] [ 2371.811011] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. [ 2371.817867] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 [ 2371.823078] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 [ 2371.830190] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 [ 2371.837307] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 [ 2371.844420] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 [ 2371.851534] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 [ 2371.858646] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 [ 2371.866707] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2371.872435] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 [ 2371.879546] PKRU: 55555554 [ 2371.882261] Call Trace: [ 2371.884719] <TASK> [ 2371.886831] tc_modify_qdisc+0x75/0x7c0 [ 2371.890667] rtnetlink_rcv_msg+0x141/0x3c0 [ 2371.894764] ? _copy_to_iter+0x1b0/0x5a0 [ 2371.898685] ? rtnl_calcit.isra.0+0x140/0x140 [ 2371.903040] netlink_rcv_skb+0x4e/0x100 [ 2371.906878] netlink_unicast+0x197/0x240 [ 2371.910797] netlink_sendmsg+0x246/0x4a0 [ 2371.914718] sock_sendmsg+0x5f/0x70 [ 2371.918207] ____sys_sendmsg+0x20f/0x280 [ 2371.922130] ? copy_msghdr_from_user+0x72/0xb0 [ 2371.926570] ___sys_sendmsg+0x7c/0xc0 [ 2371.930233] ? ___sys_recvmsg+0x89/0xc0 [ 2371.934070] __sys_sendmsg+0x59/0xa0 [ 2371.937647] do_syscall_64+0x40/0x90 [ 2371.941224] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 2371.946273] RIP: 0033:0x7fd2fc38e707 [ 2371.949847] Code: 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10 [ 2371.968521] RSP: 002b:00007fffafdf9ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e [ 2371.976070] RAX: ffffffffffffffda RBX: 0000000063359bf0 RCX: 00007fd2fc38e707 [ 2371.983183] RDX: 0000000000000000 RSI: 00007fffafdf9d50 RDI: 0000000000000003 [ 2371.990293] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 [ 2371.997406] R10: 00007fd2fc28d670 R11: 0000000000000246 R12: 0000000000000001 [ 2372.004520] R13: 00005583e730c476 R14: 00005583e730c48a R15: 00005583e7333280 [ 2372.011637] </TASK> [ 2372.013830] Modules linked in: sch_taprio bnep 8021q bluetooth ecdh_generic ecc ecryptfs nfsd sch_fq_codel uio uhid iwlwifi cfg80211 i915 x86_pkg_temp_thermal kvm_intel kvm hid_sensor_als hid_sensor_incl_3d hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_magn_3d hid_sensor_trigger hid_sensor_iio_common hid_sensor_custom hid_sensor_hub atkbd mei_hdcp intel_ishtp_hid libps2 mei_wdt vivaldi_fmap dwc3 dwmac_intel stmmac e1000e ax88179_178a usbnet mii mei_me igc thunderbolt udc_core mei pcs_xpcs wdat_wdt irqbypass spi_pxa2xx_platform phylink intel_ish_ipc i2c_i801 dw_dmac tpm_crb intel_rapl_msr pcspkr dw_dmac_core i2c_smbus intel_ishtp tpm_tis parport_pc intel_pmc_core igen6_edac tpm_tis_core thermal parport i8042 tpm edac_core dwc3_pci video drm_buddy ttm drm_display_helper fuse configfs snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_pcm snd_timer snd soundcore [ 2372.092427] CR2: 0000000000000008 [ 2372.095744] ---[ end trace 0000000000000000 ]--- [ 2372.276814] RIP: 0010:taprio_leaf+0x1e/0x30 [sch_taprio] [ 2372.282140] Code: Unable to access opcode bytes at RIP 0xffffffffc1112ff4. [ 2372.288995] RSP: 0018:ffffae7f82263a28 EFLAGS: 00010206 [ 2372.294215] RAX: 0000000000000000 RBX: 0000000001000002 RCX: ffff8a704ff38000 [ 2372.301329] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8a7043f29000 [ 2372.308442] RBP: ffff8a7043f29000 R08: 0000000000000000 R09: ffffae7f82263b98 [ 2372.315550] R10: 0000000000000002 R11: ffff8a7045df0000 R12: ffff8a70519cc400 [ 2372.322663] R13: ffffae7f82263b98 R14: ffffffff9a04fb00 R15: ffff8a704ff38000 [ 2372.329774] FS: 00007fd2fc262740(0000) GS:ffff8a7790a00000(0000) knlGS:0000000000000000 [ 2372.337840] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2372.343569] CR2: ffffffffc1112ff4 CR3: 00000001053ac003 CR4: 0000000000770ef0 [ 2372.350680] PKRU: 55555554 Fixes: 1461d212ab27 ("net/sched: taprio: make qdisc_leaf() see the per-netdev-queue pfifo child qdiscs") Reported-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com> --- This patch is more to make others aware of this issue and to explain what I think is going on. Perhaps the correct solution is something else. (and that explicit refcount seems wrong, but getting warnings without it). I am questioning my sanity, I have clear memories about testing the commit above and it working fine. Reverting commit 1461d212ab27 is another alternative, but I think it's worth to keep that and fix the problem that it exposed. net/sched/sch_taprio.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-)