Re: [PATCH net-next 8/8] net: phy: improve mdiobus_stats_acct

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 27.02.2026 23:11, Heiner Kallweit wrote:
> - Remove duplicated preempt disable. Disabling preemption has been added
>    to functions like u64_stats_update_begin() in the meantime.
> - Simplify branch structure
>
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

This patch has been merged to yesterday's linux-next as commit 
1afccc5a201e ("net: phy: improve mdiobus_stats_acct"). In my tests I 
found that it introduces the following warning on 32bit machines with 
USB ethernet adapters, so the preempt disable was there for a good reason:

------------[ cut here ]------------
WARNING: ./include/linux/u64_stats_sync.h:171 at 
mdiobus_stats_acct+0x288/0x2b4, CPU#0: kworker/0:3/50
Loading compiled-in X.509 certificates
Modules linked in:
CPU: 0 UID: 0 PID: 50 Comm: kworker/0:3 Not tainted 
7.0.0-rc2-next-20260304 #12283 PREEMPT
Hardware name: Samsung Exynos (Flattened Device Tree)
Workqueue: usb_hub_wq hub_event
Call trace:
  unwind_backtrace from show_stack+0x10/0x14
  show_stack from dump_stack_lvl+0x68/0x88
  dump_stack_lvl from __warn+0x94/0x210
  __warn from warn_slowpath_fmt+0x1b0/0x1bc
  warn_slowpath_fmt from mdiobus_stats_acct+0x288/0x2b4
  mdiobus_stats_acct from __mdiobus_read+0x84/0xf0
  __mdiobus_read from mdiobus_read+0x30/0x44
  mdiobus_read from get_phy_device+0xac/0x140
  get_phy_device from mdiobus_scan+0x24/0x104
  mdiobus_scan from __mdiobus_register+0x21c/0x478
  __mdiobus_register from smsc95xx_bind+0x3f4/0x5f0
  smsc95xx_bind from usbnet_probe+0x330/0x928
  usbnet_probe from usb_probe_interface+0xec/0x318
  usb_probe_interface from really_probe+0xe0/0x424
  really_probe from __driver_probe_device+0x9c/0x1f4
  __driver_probe_device from driver_probe_device+0x30/0xc0
  driver_probe_device from __device_attach_driver+0xa8/0x140
  __device_attach_driver from bus_for_each_drv+0x84/0xdc
  bus_for_each_drv from __device_attach+0xb0/0x214
  __device_attach from device_initial_probe+0x3c/0x48
  device_initial_probe from bus_probe_device+0x24/0x80
  bus_probe_device from device_add+0x5c0/0x810
  device_add from usb_set_configuration+0x4e4/0x974
  usb_set_configuration from usb_generic_driver_probe+0x3c/0x78
  usb_generic_driver_probe from usb_probe_device+0x4c/0x14c
  usb_probe_device from really_probe+0xe0/0x424
  really_probe from __driver_probe_device+0x9c/0x1f4
  __driver_probe_device from driver_probe_device+0x30/0xc0
  driver_probe_device from __device_attach_driver+0xa8/0x140
  __device_attach_driver from bus_for_each_drv+0x84/0xdc
  bus_for_each_drv from __device_attach+0xb0/0x214
  __device_attach from device_initial_probe+0x3c/0x48
  device_initial_probe from bus_probe_device+0x24/0x80
  bus_probe_device from device_add+0x5c0/0x810
  device_add from usb_new_device+0x23c/0x4f8
  usb_new_device from hub_event+0x11dc/0x1ca4
  hub_event from process_one_work+0x24c/0x7b8
  process_one_work from worker_thread+0x1b8/0x3bc
  worker_thread from kthread+0x128/0x168
  kthread from ret_from_fork+0x14/0x28
Exception stack(0xf0a15fb0 to 0xf0a15ff8)
...
irq event stamp: 5711
hardirqs last  enabled at (5911): [<c01c6c54>] 
console_flush_one_record+0x424/0x570
hardirqs last disabled at (5943): [<c013ce4c>] handle_softirqs+0x53c/0x5c0
softirqs last  enabled at (5944): [<c013cc3c>] handle_softirqs+0x32c/0x5c0
softirqs last disabled at (6157): [<c013d07c>] __irq_exit_rcu+0x144/0x1f0
---[ end trace 0000000000000000 ]---


> ---
>   drivers/net/phy/mdio_bus.c | 11 +++--------
>   1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
> index 48c0447e6a8..b32a369cd25 100644
> --- a/drivers/net/phy/mdio_bus.c
> +++ b/drivers/net/phy/mdio_bus.c
> @@ -358,22 +358,17 @@ EXPORT_SYMBOL(of_mdio_find_bus);
>   
>   static void mdiobus_stats_acct(struct mdio_bus_stats *stats, bool op, int ret)
>   {
> -	preempt_disable();
>   	u64_stats_update_begin(&stats->syncp);
>   
>   	u64_stats_inc(&stats->transfers);
> -	if (ret < 0) {
> +	if (ret < 0)
>   		u64_stats_inc(&stats->errors);
> -		goto out;
> -	}
> -
> -	if (op)
> +	else if (op)
>   		u64_stats_inc(&stats->reads);
>   	else
>   		u64_stats_inc(&stats->writes);
> -out:
> +
>   	u64_stats_update_end(&stats->syncp);
> -	preempt_enable();
>   }
>   
>   /**

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland