[PATCH v1 1/1] regmap: irq: Set lockdep class for hierarchical IRQ domains

[PATCH v1 1/1] regmap: irq: Set lockdep class for hierarchical IRQ domains

[Andy Shevchenko]

Lockdep gives a false positive splat as it can't distinguish the lock
which is taken by different IRQ descriptors from different IRQ chips
that are organized in a way of a hierarchy:

   ======================================================
   WARNING: possible circular locking dependency detected
   6.12.0-rc5-next-20241101-00148-g9fabf8160b53 #562 Tainted: G        W
   ------------------------------------------------------
   modprobe/141 is trying to acquire lock:
   ffff899446947868 (intel_soc_pmic_bxtwc:502:(&bxtwc_regmap_config)->lock){+.+.}-{4:4}, at: regmap_update_bits_base+0x33/0x90

   but task is already holding lock:
   ffff899446947c68 (&d->lock){+.+.}-{4:4}, at: __setup_irq+0x682/0x790

   which lock already depends on the new lock.

   -> #3 (&d->lock){+.+.}-{4:4}:
   -> #2 (&desc->request_mutex){+.+.}-{4:4}:
   -> #1 (ipclock){+.+.}-{4:4}:
   -> #0 (intel_soc_pmic_bxtwc:502:(&bxtwc_regmap_config)->lock){+.+.}-{4:4}:

   Chain exists of:
     intel_soc_pmic_bxtwc:502:(&bxtwc_regmap_config)->lock --> &desc->request_mutex --> &d->lock

    Possible unsafe locking scenario:

          CPU0                    CPU1
          ----                    ----
     lock(&d->lock);
                                  lock(&desc->request_mutex);
                                  lock(&d->lock);
     lock(intel_soc_pmic_bxtwc:502:(&bxtwc_regmap_config)->lock);

    *** DEADLOCK ***

   3 locks held by modprobe/141:
    #0: ffff8994419368f8 (&dev->mutex){....}-{4:4}, at: __driver_attach+0xf6/0x250
    #1: ffff89944690b250 (&desc->request_mutex){+.+.}-{4:4}, at: __setup_irq+0x1a2/0x790
    #2: ffff899446947c68 (&d->lock){+.+.}-{4:4}, at: __setup_irq+0x682/0x790

Set a lockdep class when we map the IRQ so that it doesn't warn about
a lockdep bug that doesn't exist.

Fixes: 4af8be67fd99 ("regmap: Convert regmap_irq to use irq_domain")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/base/regmap/regmap-irq.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/base/regmap/regmap-irq.c b/drivers/base/regmap/regmap-irq.c
index 33ec28e3a802..0bcd81389a29 100644
--- a/drivers/base/regmap/regmap-irq.c
+++ b/drivers/base/regmap/regmap-irq.c
@@ -511,12 +511,16 @@ static irqreturn_t regmap_irq_thread(int irq, void *d)
 		return IRQ_NONE;
 }
 
+static struct lock_class_key regmap_irq_lock_class;
+static struct lock_class_key regmap_irq_request_class;
+
 static int regmap_irq_map(struct irq_domain *h, unsigned int virq,
 			  irq_hw_number_t hw)
 {
 	struct regmap_irq_chip_data *data = h->host_data;
 
 	irq_set_chip_data(virq, data);
+	irq_set_lockdep_class(virq, &regmap_irq_lock_class, &regmap_irq_request_class);
 	irq_set_chip(virq, &data->irq_chip);
 	irq_set_nested_thread(virq, 1);
 	irq_set_parent(virq, data->irq);
-- 
2.43.0.rc1.1336.g36b5255a03ac

Re: [PATCH v1 1/1] regmap: irq: Set lockdep class for hierarchical IRQ domains

[Mark Brown]

On Fri, 01 Nov 2024 18:55:53 +0200, Andy Shevchenko wrote:
> Lockdep gives a false positive splat as it can't distinguish the lock
> which is taken by different IRQ descriptors from different IRQ chips
> that are organized in a way of a hierarchy:
> 
>    ======================================================
>    WARNING: possible circular locking dependency detected
>    6.12.0-rc5-next-20241101-00148-g9fabf8160b53 #562 Tainted: G        W
>    ------------------------------------------------------
>    modprobe/141 is trying to acquire lock:
>    ffff899446947868 (intel_soc_pmic_bxtwc:502:(&bxtwc_regmap_config)->lock){+.+.}-{4:4}, at: regmap_update_bits_base+0x33/0x90
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git for-next

Thanks!

[1/1] regmap: irq: Set lockdep class for hierarchical IRQ domains
      commit: 953e549471cabc9d4980f1da2e9fa79f4c23da06

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark