Re: [PATCH] irqchip/meson-gpio: Fix HARDIRQ-safe -> HARDIRQ-unsafe lock order

Jerome Brunet
2020-04-14T15:52:39Z

On Tue 14 Apr 2020 at 15:20, Marc Zyngier <maz@kernel.org> wrote:

> On Tue, 7 Apr 2020 15:46:58 +0100
> Marc Zyngier <maz@kernel.org> wrote:
>
> +Jerome, Martin,
>
>> Running a lockedp-enabled kernel on a vim3l board (Amlogic SM1)
>> leads to the following splat:
>>
>> [ 13.557138] WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
>> [ 13.587485] ip/456 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
>> [ 13.625922] ffff000059908cf0 (&irq_desc_lock_class){-.-.}-{2:2}, at: __setup_irq+0xf8/0x8d8
>> [ 13.632273] which would create a new lock dependency:
>> [ 13.637272] (&irq_desc_lock_class){-.-.}-{2:2} -> (&ctl->lock){+.+.}-{2:2}
>> [ 13.644209]
>> [ 13.644209] but this new dependency connects a HARDIRQ-irq-safe lock:
>> [ 13.654122] (&irq_desc_lock_class){-.-.}-{2:2}
>> [ 13.654125]
>> [ 13.654125] ... which became HARDIRQ-irq-safe at:
>> [ 13.664759] lock_acquire+0xec/0x368
>> [ 13.666926] _raw_spin_lock+0x60/0x88
>> [ 13.669979] handle_fasteoi_irq+0x30/0x178
>> [ 13.674082] generic_handle_irq+0x38/0x50
>> [ 13.678098] __handle_domain_irq+0x6c/0xc8
>> [ 13.682209] gic_handle_irq+0x5c/0xb0
>> [ 13.685872] el1_irq+0xd0/0x180
>> [ 13.689010] arch_cpu_idle+0x40/0x220
>> [ 13.692732] default_idle_call+0x54/0x60
>> [ 13.696677] do_idle+0x23c/0x2e8
>> [ 13.699903] cpu_startup_entry+0x30/0x50
>> [ 13.703852] rest_init+0x1e0/0x2b4
>> [ 13.707301] arch_call_rest_init+0x18/0x24
>> [ 13.711449] start_kernel+0x4ec/0x51c
>> [ 13.715167]
>> [ 13.715167] to a HARDIRQ-irq-unsafe lock:
>> [ 13.722426] (&ctl->lock){+.+.}-{2:2}
>> [ 13.722430]
>> [ 13.722430] ... which became HARDIRQ-irq-unsafe at:
>> [ 13.732319] ...
>> [ 13.732324] lock_acquire+0xec/0x368
>> [ 13.735985] _raw_spin_lock+0x60/0x88
>> [ 13.739452] meson_gpio_irq_domain_alloc+0xcc/0x290
>> [ 13.744392] irq_domain_alloc_irqs_hierarchy+0x24/0x60
>> [ 13.749586] __irq_domain_alloc_irqs+0x160/0x2f0
>> [ 13.754254] irq_create_fwspec_mapping+0x118/0x320
>> [ 13.759073] irq_create_of_mapping+0x78/0xa0
>> [ 13.763360] of_irq_get+0x6c/0x80
>> [ 13.766701] of_mdiobus_register_phy+0x10c/0x238 [of_mdio]
>> [ 13.772227] of_mdiobus_register+0x158/0x380 [of_mdio]
>> [ 13.777388] mdio_mux_init+0x180/0x2e8 [mdio_mux]
>> [ 13.782128] g12a_mdio_mux_probe+0x290/0x398 [mdio_mux_meson_g12a]
>> [ 13.788349] platform_drv_probe+0x5c/0xb0
>> [ 13.792379] really_probe+0xe4/0x448
>> [ 13.795979] driver_probe_device+0xe8/0x140
>> [ 13.800189] __device_attach_driver+0x94/0x120
>> [ 13.804639] bus_for_each_drv+0x84/0xd8
>> [ 13.808474] __device_attach+0xe4/0x168
>> [ 13.812361] device_initial_probe+0x1c/0x28
>> [ 13.816592] bus_probe_device+0xa4/0xb0
>> [ 13.820430] deferred_probe_work_func+0xa8/0x100
>> [ 13.825064] process_one_work+0x264/0x688
>> [ 13.829088] worker_thread+0x4c/0x458
>> [ 13.832768] kthread+0x154/0x158
>> [ 13.836018] ret_from_fork+0x10/0x18
>> [ 13.839612]
>> [ 13.839612] other info that might help us debug this:
>> [ 13.839612]
>> [ 13.850354] Possible interrupt unsafe locking scenario:
>> [ 13.850354]
>> [ 13.855720] CPU0 CPU1
>> [ 13.858774] ---- ----
>> [ 13.863242] lock(&ctl->lock);
>> [ 13.866330] local_irq_disable();
>> [ 13.872233] lock(&irq_desc_lock_class);
>> [ 13.878705] lock(&ctl->lock);
>> [ 13.884297] <Interrupt>
>> [ 13.886857] lock(&irq_desc_lock_class);
>> [ 13.891014]
>> [ 13.891014] *** DEADLOCK ***
>>
>> The issue can occur when CPU1 is doing something like irq_set_type()
>> and CPU0 performing an interrupt allocation, for example. Taking
>> an interrupt (like the one being reconfigured) would lead to a
>> deadlock.

Just to make sure I understand
* the 1st trace is a CPU getting interrupted while setting the irq type
* the 2nd trace is another CPU trying to allocate an irq for network PHY.

>>
>> A solution to this is:
>>
>> - Reorder the locking so that meson_gpio_irq_update_bits takes the lock
>> itself at all times, instead of relying on the caller to lock or not,
>> hence making the RMW sequence atomic,
>>
>> - Rework the critical section in meson_gpio_irq_request_channel to only
>> cover the allocation itself, and let the gpio_irq_sel_pin callback
>> deal with its own locking if required,
>>
>> - Take the private spin-lock with interrupts disabled at all times

Looks like the only safe path if I understand correctly.
The patch below looks good to me.

>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>

Thanks for the fix Marc.

Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>

>> ---
>> drivers/irqchip/irq-meson-gpio.c | 18 ++++++++++--------
>> 1 file changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-meson-gpio.c b/drivers/irqchip/irq-meson-gpio.c
>> index ccc7f823911b..bc7aebcc96e9 100644
>> --- a/drivers/irqchip/irq-meson-gpio.c
>> +++ b/drivers/irqchip/irq-meson-gpio.c
>> @@ -144,12 +144,17 @@ struct meson_gpio_irq_controller {
>> static void meson_gpio_irq_update_bits(struct meson_gpio_irq_controller *ctl,
>> unsigned int reg, u32 mask, u32 val)
>> {
>> + unsigned long flags;
>> u32 tmp;
>>
>> + spin_lock_irqsave(&ctl->lock, flags);
>> +
>> tmp = readl_relaxed(ctl->base + reg);
>> tmp &= ~mask;
>> tmp |= val;
>> writel_relaxed(tmp, ctl->base + reg);
>> +
>> + spin_unlock_irqrestore(&ctl->lock, flags);
>> }
>>
>> static void meson_gpio_irq_init_dummy(struct meson_gpio_irq_controller *ctl)
>> @@ -196,14 +201,15 @@ meson_gpio_irq_request_channel(struct meson_gpio_irq_controller *ctl,
>> unsigned long hwirq,
>> u32 **channel_hwirq)
>> {
>> + unsigned long flags;
>> unsigned int idx;
>>
>> - spin_lock(&ctl->lock);
>> + spin_lock_irqsave(&ctl->lock, flags);
>>
>> /* Find a free channel */
>> idx = find_first_zero_bit(ctl->channel_map, NUM_CHANNEL);
>> if (idx >= NUM_CHANNEL) {
>> - spin_unlock(&ctl->lock);
>> + spin_unlock_irqrestore(&ctl->lock, flags);
>> pr_err("No channel available\n");
>> return -ENOSPC;
>> }
>> @@ -211,6 +217,8 @@ meson_gpio_irq_request_channel(struct meson_gpio_irq_controller *ctl,
>> /* Mark the channel as used */
>> set_bit(idx, ctl->channel_map);
>>
>> + spin_unlock_irqrestore(&ctl->lock, flags);
>> +
>> /*
>> * Setup the mux of the channel to route the signal of the pad
>> * to the appropriate input of the GIC
>> @@ -225,8 +233,6 @@ meson_gpio_irq_request_channel(struct meson_gpio_irq_controller *ctl,
>> */
>> *channel_hwirq = &(ctl->channel_irqs[idx]);
>>
>> - spin_unlock(&ctl->lock);
>> -
>> pr_debug("hwirq %lu assigned to channel %d - irq %u\n",
>> hwirq, idx, **channel_hwirq);
>>
>> @@ -287,13 +293,9 @@ static int meson_gpio_irq_type_setup(struct meson_gpio_irq_controller *ctl,
>> val |= REG_EDGE_POL_LOW(params, idx);
>> }
>>
>> - spin_lock(&ctl->lock);
>> -
>> meson_gpio_irq_update_bits(ctl, REG_EDGE_POL,
>> REG_EDGE_POL_MASK(params, idx), val);
>>
>> - spin_unlock(&ctl->lock);
>> -
>> return 0;
>> }
>>