Re: [PATCH net] net: dsa: mt7530: fix .get_stats64 sleeping in atomic context

[Daniel Golle <daniel@makrotopia.org>]

On Fri, Apr 17, 2026 at 07:35:46AM +0000, Chester A. Unal wrote:
> On 17 April 2026 04:55:57 WEST, Daniel Golle <daniel@makrotopia.org> wrote:
> >The .get_stats64 callback runs in atomic context, but on
> >MDIO-connected switches every register read acquires the MDIO bus
> >mutex, which can sleep:
> >[   12.645973] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:609
> >[   12.654442] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 759, name: grep
> >[   12.663377] preempt_count: 0, expected: 0
> >[   12.667410] RCU nest depth: 1, expected: 0
> >[   12.671511] INFO: lockdep is turned off.
> >[   12.675441] CPU: 0 UID: 0 PID: 759 Comm: grep Tainted: G S      W           7.0.0+ #0 PREEMPT
> >[   12.675453] Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN
> >[   12.675456] Hardware name: Bananapi BPI-R64 (DT)
> >[   12.675459] Call trace:
> >[   12.675462]  show_stack+0x14/0x1c (C)
> >[   12.675477]  dump_stack_lvl+0x68/0x8c
> >[   12.675487]  dump_stack+0x14/0x1c
> >[   12.675495]  __might_resched+0x14c/0x220
> >[   12.675504]  __might_sleep+0x44/0x80
> >[   12.675511]  __mutex_lock+0x50/0xb10
> >[   12.675523]  mutex_lock_nested+0x20/0x30
> >[   12.675532]  mt7530_get_stats64+0x40/0x2ac
> >[   12.675542]  dsa_user_get_stats64+0x2c/0x40
> >[   12.675553]  dev_get_stats+0x44/0x1e0
> >[   12.675564]  dev_seq_printf_stats+0x24/0xe0
> >[   12.675575]  dev_seq_show+0x14/0x3c
> >[   12.675583]  seq_read_iter+0x37c/0x480
> >[   12.675595]  seq_read+0xd0/0xec
> >[   12.675605]  proc_reg_read+0x94/0xe4
> >[   12.675615]  vfs_read+0x98/0x29c
> >[   12.675625]  ksys_read+0x54/0xdc
> >[   12.675633]  __arm64_sys_read+0x18/0x20
> >[   12.675642]  invoke_syscall.constprop.0+0x54/0xec
> >[   12.675653]  do_el0_svc+0x3c/0xb4
> >[   12.675662]  el0_svc+0x38/0x200
> >[   12.675670]  el0t_64_sync_handler+0x98/0xdc
> >[   12.675679]  el0t_64_sync+0x158/0x15c
> >
> >For MDIO-connected switches, poll MIB counters asynchronously using a
> >delayed workqueue every second and let .get_stats64 return the cached
> >values under a per-port spinlock. A mod_delayed_work() call on each
                 ^^^^^^^^^^^^^^^^^^^
Just noticed I forgot to update the commit message when changing the
implementation to use a single shared spinlock for all ports...

I'll send v2 tomorrow fixing that, and what ever else comes up, if
anything.

> >read triggers an immediate refresh so counters stay responsive when
> >queried more frequently.
> >
> >MMIO-connected switches (MT7988, EN7581, AN7583) are not affected
> >because their regmap does not sleep, so they continue to read MIB
> >counters directly in .get_stats64.
> >
> >Fixes: 88c810f35ed5 ("net: dsa: mt7530: implement .get_stats64")
> >Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> >---
> >This bug highlights a bigger problem and the actual cause:
> >Locking in the mt7530 driver deserves a cleanup, and refactoring
> >towards cleanly and directly using the regmap API.
> >I've prepared this already and am going to submit a series doing
> >most of that using Coccinelle semantic patches once net-next opens
> >again.
> 
> Acked-by: Chester A. Unal <chester.a.unal@arinc9.com>
> 
> Chester A.