Re: [PATCH net v2] net: dsa: mt7530: fix .get_stats64 sleeping in atomic context

Simon Horman
2026-04-22T18:23:08Z

On Sun, Apr 19, 2026 at 11:43:05AM +0100, Daniel Golle 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 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>
> Acked-by: Chester A. Unal <chester.a.unal@arinc9.com>
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>
> ---
> v2:
> * use spin_lock_bh()/spin_unlock_bh() to prevent potential deadlock
> * rate-limit mod_delayed_work() refresh to at most once per 100ms
> * move cancel_delayed_work_sync() after dsa_unregister_switch()
> * add mt753x_teardown() callback to cancel the stats work
> * fix commit message

FWIIW, I looked over the feedback generated by Sashiko for this patch,
and I believe the issues it flags are false positives.