Re: [PATCH] gpio: omap: Silence lockdep "Invalid wait context"

On Mon, Nov 25, 2024 at 9:05 AM A. Sverdlin alexander.sverdlin@siemens.com wrote:

From: Alexander Sverdlin alexander.sverdlin@siemens.com

The problem apparetly has been known since the conversion to raw_spin_lock() (commit 4dbada2be460 ("gpio: omap: use raw locks for locking")).

Symptom:

[ BUG: Invalid wait context ] 5.10.214

---

swapper/1 is trying to lock: (enable_lock){....}-{3:3}, at: clk_enable_lock other info that might help us debug this: context-{5:5} 2 locks held by swapper/1: #0: (&dev->mutex){....}-{4:4}, at: device_driver_attach #1: (&bank->lock){....}-{2:2}, at: omap_gpio_set_config stack backtrace: CPU: 0 PID: 1 Comm: swapper Not tainted 5.10.214 Hardware name: Generic AM33XX (Flattened Device Tree) unwind_backtrace show_stack __lock_acquire lock_acquire.part.0 _raw_spin_lock_irqsave clk_enable_lock clk_enable omap_gpio_set_config gpio_keys_setup_key gpio_keys_probe platform_drv_probe really_probe driver_probe_device device_driver_attach __driver_attach bus_for_each_dev bus_add_driver driver_register do_one_initcall do_initcalls kernel_init_freeable kernel_init

Problematic spin_lock_irqsave(&enable_lock, ...) is being called by clk_enable()/clk_disable() in omap2_set_gpio_debounce() and omap_clear_gpio_debounce().

For omap2_set_gpio_debounce() it's possible to move raw_spin_lock_irqsave(&bank->lock, ...) inside omap2_set_gpio_debounce() so that the locks nest as follows:

clk_enable(bank->dbck) raw_spin_lock_irqsave(&bank->lock, ...) raw_spin_unlock_irqrestore() clk_disable()

Two call-sites of omap_clear_gpio_debounce() are more convoluted, but one can take the advantage of the nesting nature of clk_enable()/clk_disable(), so that the inner clk_disable() becomes lockless:

clk_enable(bank->dbck) <-- only to clk_enable_lock() raw_spin_lock_irqsave(&bank->lock, ...) omap_clear_gpio_debounce() clk_disable() <-- becomes lockless raw_spin_unlock_irqrestore() clk_disable()

Cc: stable@vger.kernel.org Fixes: 4dbada2be460 ("gpio: omap: use raw locks for locking") Signed-off-by: Alexander Sverdlin alexander.sverdlin@siemens.com

---

drivers/gpio/gpio-omap.c | 35 ++++++++++++++++++++++++++++++----- 1 file changed, 30 insertions(+), 5 deletions(-)

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c index 7ad4534054962..f9e502aa57753 100644 --- a/drivers/gpio/gpio-omap.c +++ b/drivers/gpio/gpio-omap.c @@ -181,6 +181,7 @@ static inline void omap_gpio_dbck_disable(struct gpio_bank *bank) static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, unsigned debounce) {

•   unsigned long           flags;
    u32                     val;
    u32                     l;
    bool                    enable = !!debounce;
  

@@ -196,13 +197,18 @@ static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset,

    l = BIT(offset);

•   /*
  

•    * Ordering is important here: clk_enable() calls spin_lock_irqsave(),
  

•    * therefore it must be outside of the following raw_spin_lock_irqsave()
  

•    */
    clk_enable(bank->dbck);
  

•   raw_spin_lock_irqsave(&bank->lock, flags);
  

•   writel_relaxed(debounce, bank->base + bank->regs->debounce);
  
    val = omap_gpio_rmw(bank->base + bank->regs->debounce_en, l, enable);
    bank->dbck_enable_mask = val;
  
  

•   clk_disable(bank->dbck);
    /*
     * Enable debounce clock per module.
     * This call is mandatory because in omap_gpio_request() when
  

@@ -217,6 +223,9 @@ static int omap2_set_gpio_debounce(struct gpio_bank *bank, unsigned offset, bank->context.debounce_en = val; }

•   raw_spin_unlock_irqrestore(&bank->lock, flags);
  

•   clk_disable(bank->dbck);
  

This part looks pretty clear to me.

    return 0;

}

@@ -647,6 +656,13 @@ static void omap_gpio_irq_shutdown(struct irq_data *d) unsigned long flags; unsigned offset = d->hwirq;

•   /*
  

•    * Enable the clock here so that the nested clk_disable() in the
  

•    * following omap_clear_gpio_debounce() is lockless
  

•    */
  

•   if (bank->dbck_flag)
  

•           clk_enable(bank->dbck);
  

But this looks like a functional change. You effectively bump the clock enable count but don't add a corresponding clk_disable() in the affected path. Is the clock ever actually disabled then?

Am I not getting something?

Bart

    raw_spin_lock_irqsave(&bank->lock, flags);
    bank->irq_usage &= ~(BIT(offset));
    omap_set_gpio_triggering(bank, offset, IRQ_TYPE_NONE);

@@ -656,6 +672,9 @@ static void omap_gpio_irq_shutdown(struct irq_data *d) omap_clear_gpio_debounce(bank, offset); omap_disable_gpio_module(bank, offset); raw_spin_unlock_irqrestore(&bank->lock, flags);

•   if (bank->dbck_flag)
  

•           clk_disable(bank->dbck);
  

}

static void omap_gpio_irq_bus_lock(struct irq_data *data) @@ -827,6 +846,13 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset) struct gpio_bank *bank = gpiochip_get_data(chip); unsigned long flags;

•   /*
  

•    * Enable the clock here so that the nested clk_disable() in the
  

•    * following omap_clear_gpio_debounce() is lockless
  

•    */
  

•   if (bank->dbck_flag)
  

•           clk_enable(bank->dbck);
  

•   raw_spin_lock_irqsave(&bank->lock, flags);
    bank->mod_usage &= ~(BIT(offset));
    if (!LINE_USED(bank->irq_usage, offset)) {
  

@@ -836,6 +862,9 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset) omap_disable_gpio_module(bank, offset); raw_spin_unlock_irqrestore(&bank->lock, flags);

•   if (bank->dbck_flag)
  

•           clk_disable(bank->dbck);
  

•   pm_runtime_put(chip->parent);
  

}

@@ -913,15 +942,11 @@ static int omap_gpio_debounce(struct gpio_chip *chip, unsigned offset, unsigned debounce) { struct gpio_bank *bank;

•   unsigned long flags;
    int ret;
  
    bank = gpiochip_get_data(chip);
  
  

•   raw_spin_lock_irqsave(&bank->lock, flags);
    ret = omap2_set_gpio_debounce(bank, offset, debounce);
  

•   raw_spin_unlock_irqrestore(&bank->lock, flags);
  

•   if (ret)
            dev_info(chip->parent,
                     "Could not set line %u debounce to %u microseconds (%d)",
  

-- 2.47.0