[PATCH net-next v2 1/5] net: add dev->bql flag to allow BQL sysfs for IFF_NO_QUEUE devices

[PATCH net-next v2 1/5] net: add dev->bql flag to allow BQL sysfs for IFF_NO_QUEUE devices

[hawk]

From: Jesper Dangaard Brouer <hawk@kernel.org>

Virtual devices with IFF_NO_QUEUE or lltx are excluded from BQL sysfs
by netdev_uses_bql(), since they traditionally lack real hardware
queues. However, some virtual devices like veth implement a real
ptr_ring FIFO with NAPI processing and benefit from BQL to limit
in-flight bytes and reduce latency.

Add a per-device 'bql' bitfield boolean in the priv_flags_slow section
of struct net_device. When set, it overrides the IFF_NO_QUEUE/lltx
exclusion and exposes BQL sysfs entries (/sys/class/net/<dev>/queues/
tx-<n>/byte_queue_limits/). The flag is still gated on CONFIG_BQL.

This allows drivers that use BQL despite being IFF_NO_QUEUE to opt in
to sysfs visibility for monitoring and debugging.

Signed-off-by: Jesper Dangaard Brouer <hawk@kernel.org>
Tested-by: Jonas Köppeler <j.koeppeler@tu-berlin.de>
---
 Documentation/networking/net_cachelines/net_device.rst | 1 +
 include/linux/netdevice.h                              | 2 ++
 net/core/net-sysfs.c                                   | 8 +++++++-
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index 1c19bb7705df..b775d3235a2d 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -170,6 +170,7 @@ unsigned_long:1                     see_all_hwtstamp_requests
 unsigned_long:1                     change_proto_down
 unsigned_long:1                     netns_immutable
 unsigned_long:1                     fcoe_mtu
+unsigned_long:1                     bql                                                                 netdev_uses_bql(net-sysfs.c)
 struct list_head                    net_notifier_list
 struct macsec_ops*                  macsec_ops
 struct udp_tunnel_nic_info*         udp_tunnel_nic_info
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 47417b2d48a4..7a1a491ecdd5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2048,6 +2048,7 @@ enum netdev_reg_state {
  *	@change_proto_down: device supports setting carrier via IFLA_PROTO_DOWN
  *	@netns_immutable: interface can't change network namespaces
  *	@fcoe_mtu:	device supports maximum FCoE MTU, 2158 bytes
+ *	@bql:		device uses BQL (DQL sysfs) despite having IFF_NO_QUEUE
  *
  *	@net_notifier_list:	List of per-net netdev notifier block
  *				that follow this device when it is moved
@@ -2462,6 +2463,7 @@ struct net_device {
 	unsigned long		change_proto_down:1;
 	unsigned long		netns_immutable:1;
 	unsigned long		fcoe_mtu:1;
+	unsigned long		bql:1;
 
 	struct list_head	net_notifier_list;
 
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index e430645748a7..4360efc8f241 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1945,10 +1945,16 @@ static const struct kobj_type netdev_queue_ktype = {
 
 static bool netdev_uses_bql(const struct net_device *dev)
 {
+	if (!IS_ENABLED(CONFIG_BQL))
+		return false;
+
+	if (dev->bql)
+		return true;
+
 	if (dev->lltx || (dev->priv_flags & IFF_NO_QUEUE))
 		return false;
 
-	return IS_ENABLED(CONFIG_BQL);
+	return true;
 }
 
 static int netdev_queue_add_kobject(struct net_device *dev, int index)
-- 
2.43.0

[syzbot ci] Re: veth: add Byte Queue Limits (BQL) support

[syzbot ci]

syzbot ci has tested the following series

[v2] veth: add Byte Queue Limits (BQL) support
https://lore.kernel.org/all/20260413094442.1376022-1-hawk@kernel.org
* [PATCH net-next v2 1/5] net: add dev->bql flag to allow BQL sysfs for IFF_NO_QUEUE devices
* [PATCH net-next v2 2/5] veth: implement Byte Queue Limits (BQL) for latency reduction
* [PATCH net-next v2 3/5] veth: add tx_timeout watchdog as BQL safety net
* [PATCH net-next v2 4/5] net: sched: add timeout count to NETDEV WATCHDOG message
* [PATCH net-next v2 5/5] selftests: net: add veth BQL stress test

and found the following issue:
WARNING in veth_napi_del_range

Full report is available here:
https://ci.syzbot.org/series/ee732006-8545-4abd-a105-b4b1592a7baf

***

WARNING in veth_napi_del_range

tree:      net-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
base:      8806d502e0a7e7d895b74afbd24e8550a65a2b17
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/90743a26-f003-44cf-abcc-5991c47588b2/config
syz repro: https://ci.syzbot.org/findings/d068bfb2-9f8b-466a-95b4-cd7e7b00006c/syz_repro

------------[ cut here ]------------
index >= dev->num_tx_queues
WARNING: ./include/linux/netdevice.h:2672 at netdev_get_tx_queue include/linux/netdevice.h:2672 [inline], CPU#0: syz.1.27/6002
WARNING: ./include/linux/netdevice.h:2672 at veth_napi_del_range+0x3b7/0x4e0 drivers/net/veth.c:1142, CPU#0: syz.1.27/6002
Modules linked in:
CPU: 0 UID: 0 PID: 6002 Comm: syz.1.27 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:netdev_get_tx_queue include/linux/netdevice.h:2672 [inline]
RIP: 0010:veth_napi_del_range+0x3b7/0x4e0 drivers/net/veth.c:1142
Code: 00 e8 ad 96 69 fe 44 39 6c 24 10 74 5e e8 41 61 44 fb 41 ff c5 49 bc 00 00 00 00 00 fc ff df e9 6d ff ff ff e8 2a 61 44 fb 90 <0f> 0b 90 42 80 3c 23 00 75 8e eb 94 48 8b 0c 24 80 e1 07 80 c1 03
RSP: 0018:ffffc90003adf918 EFLAGS: 00010293
RAX: ffffffff86814ec6 RBX: 1ffff110227a6c03 RCX: ffff888103a857c0
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002
RBP: 1ffff110227a6c9a R08: ffff888113f01ab7 R09: 0000000000000000
R10: ffff888113f01a98 R11: ffffed10227e0357 R12: dffffc0000000000
R13: 0000000000000002 R14: 0000000000000002 R15: ffff888113d36018
FS:  000055555ea16500(0000) GS:ffff88818de4a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efc287456b8 CR3: 000000010cdd0000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 veth_napi_del drivers/net/veth.c:1153 [inline]
 veth_disable_xdp+0x1b0/0x310 drivers/net/veth.c:1255
 veth_xdp_set drivers/net/veth.c:1693 [inline]
 veth_xdp+0x48e/0x730 drivers/net/veth.c:1717
 dev_xdp_propagate+0x125/0x260 net/core/dev_api.c:348
 bond_xdp_set drivers/net/bonding/bond_main.c:5715 [inline]
 bond_xdp+0x3ca/0x830 drivers/net/bonding/bond_main.c:5761
 dev_xdp_install+0x42c/0x600 net/core/dev.c:10387
 dev_xdp_detach_link net/core/dev.c:10579 [inline]
 bpf_xdp_link_release+0x362/0x540 net/core/dev.c:10595
 bpf_link_free+0x103/0x480 kernel/bpf/syscall.c:3292
 bpf_link_put_direct kernel/bpf/syscall.c:3344 [inline]
 bpf_link_release+0x6b/0x80 kernel/bpf/syscall.c:3351
 __fput+0x44f/0xa70 fs/file_table.c:469
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5bda39c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdca2969e8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f5bda617da0 RCX: 00007f5bda39c819
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f5bda617da0 R08: 00007f5bda616128 R09: 0000000000000000
R10: 000000000003fd78 R11: 0000000000000246 R12: 0000000000010fb8
R13: 00007f5bda61609c R14: 0000000000010cdd R15: 00007ffdca296af0
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

To test a patch for this bug, please reply with `#syz test`
(should be on a separate line).

The patch should be attached to the email.
Note: arguments like custom git repos and branches are not supported.

Re: [syzbot ci] Re: veth: add Byte Queue Limits (BQL) support

[Jesper Dangaard Brouer]

[-- Attachment #1: Type: text/plain, Size: 4594 bytes --]



On 13/04/2026 21.49, syzbot ci wrote:
> syzbot ci has tested the following series
> 
> [v2] veth: add Byte Queue Limits (BQL) support
> https://lore.kernel.org/all/20260413094442.1376022-1-hawk@kernel.org
> * [PATCH net-next v2 1/5] net: add dev->bql flag to allow BQL sysfs for IFF_NO_QUEUE devices
> * [PATCH net-next v2 2/5] veth: implement Byte Queue Limits (BQL) for latency reduction
> * [PATCH net-next v2 3/5] veth: add tx_timeout watchdog as BQL safety net
> * [PATCH net-next v2 4/5] net: sched: add timeout count to NETDEV WATCHDOG message
> * [PATCH net-next v2 5/5] selftests: net: add veth BQL stress test
> 
> and found the following issue:
> WARNING in veth_napi_del_range
> 
> Full report is available here:
> https://ci.syzbot.org/series/ee732006-8545-4abd-a105-b4b1592a7baf
> 
> ***
> 
> WARNING in veth_napi_del_range
>

Attached a reproducer myself.
- I have V3 ready see below for diff

> tree:      net-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
> base:      8806d502e0a7e7d895b74afbd24e8550a65a2b17
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/90743a26-f003-44cf-abcc-5991c47588b2/config
> syz repro: https://ci.syzbot.org/findings/d068bfb2-9f8b-466a-95b4-cd7e7b00006c/syz_repro
> 
> ------------[ cut here ]------------
> index >= dev->num_tx_queues
> WARNING: ./include/linux/netdevice.h:2672 at netdev_get_tx_queue include/linux/netdevice.h:2672 [inline], CPU#0: syz.1.27/6002
> WARNING: ./include/linux/netdevice.h:2672 at veth_napi_del_range+0x3b7/0x4e0 drivers/net/veth.c:1142, CPU#0: syz.1.27/6002
> Modules linked in:
> CPU: 0 UID: 0 PID: 6002 Comm: syz.1.27 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> RIP: 0010:netdev_get_tx_queue include/linux/netdevice.h:2672 [inline]
> RIP: 0010:veth_napi_del_range+0x3b7/0x4e0 drivers/net/veth.c:1142
> Code: 00 e8 ad 96 69 fe 44 39 6c 24 10 74 5e e8 41 61 44 fb 41 ff c5 49 bc 00 00 00 00 00 fc ff df e9 6d ff ff ff e8 2a 61 44 fb 90 <0f> 0b 90 42 80 3c 23 00 75 8e eb 94 48 8b 0c 24 80 e1 07 80 c1 03
> RSP: 0018:ffffc90003adf918 EFLAGS: 00010293
> RAX: ffffffff86814ec6 RBX: 1ffff110227a6c03 RCX: ffff888103a857c0
> RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002
> RBP: 1ffff110227a6c9a R08: ffff888113f01ab7 R09: 0000000000000000
> R10: ffff888113f01a98 R11: ffffed10227e0357 R12: dffffc0000000000
> R13: 0000000000000002 R14: 0000000000000002 R15: ffff888113d36018
> FS:  000055555ea16500(0000) GS:ffff88818de4a000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007efc287456b8 CR3: 000000010cdd0000 CR4: 00000000000006f0
> Call Trace:
>   <TASK>
>   veth_napi_del drivers/net/veth.c:1153 [inline]
>   veth_disable_xdp+0x1b0/0x310 drivers/net/veth.c:1255
>   veth_xdp_set drivers/net/veth.c:1693 [inline]
>   veth_xdp+0x48e/0x730 drivers/net/veth.c:1717
>   dev_xdp_propagate+0x125/0x260 net/core/dev_api.c:348
>   bond_xdp_set drivers/net/bonding/bond_main.c:5715 [inline]
>   bond_xdp+0x3ca/0x830 drivers/net/bonding/bond_main.c:5761
>   dev_xdp_install+0x42c/0x600 net/core/dev.c:10387
>   dev_xdp_detach_link net/core/dev.c:10579 [inline]
>   bpf_xdp_link_release+0x362/0x540 net/core/dev.c:10595
>   bpf_link_free+0x103/0x480 kernel/bpf/syscall.c:3292
>   bpf_link_put_direct kernel/bpf/syscall.c:3344 [inline]
>   bpf_link_release+0x6b/0x80 kernel/bpf/syscall.c:3351
>   __fput+0x44f/0xa70 fs/file_table.c:469
>   task_work_run+0x1d9/0x270 kernel/task_work.c:233


The BQL reset loop in veth_napi_del_range() iterates
dev->real_num_rx_queues but indexes into peer's TX queues,
which goes out of bounds when the peer has fewer TX queues
(e.g. veth enslaved to a bond with XDP).

Fix is to clamp the loop to the peer's real_num_tx_queues.
Will be included in the V3 submission.

#syz test

---
  drivers/net/veth.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 911e7e36e166..9d7b085c9548 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1138,7 +1138,9 @@ static void veth_napi_del_range(struct net_device 
*dev, int start, int end)
  	 */
  	peer = rtnl_dereference(priv->peer);
  	if (peer) {
-		for (i = start; i < end; i++)
+		int peer_end = min(end, (int)peer->real_num_tx_queues);
+
+		for (i = start; i < peer_end; i++)
  			netdev_tx_reset_queue(netdev_get_tx_queue(peer, i));
  	}



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Re: Re: [syzbot ci] Re: veth: add Byte Queue Limits (BQL) support

[syzbot ci]

Please attach the patch to act upon.