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

Chester A. Unal
2026-04-17T07:36:08Z

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
>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.