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

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

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

--
2.25.1
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