On Sun, Feb 17, 2019 at 07:11:43PM +0100, Andrew Lunn wrote:
> The following false positive lockdep splat has been observed.
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.20.0+ #302 Not tainted
> ------------------------------------------------------
> systemd-udevd/160 is trying to acquire lock:
> edea6080 (&chip->reg_lock){+.+.}, at: __setup_irq+0x640/0x704
>
> but task is already holding lock:
> edff0340 (&desc->request_mutex){+.+.}, at: __setup_irq+0xa0/0x704
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&desc->request_mutex){+.+.}:
> mutex_lock_nested+0x1c/0x24
> __setup_irq+0xa0/0x704
> request_threaded_irq+0xd0/0x150
> mv88e6xxx_probe+0x41c/0x694 [mv88e6xxx]
> mdio_probe+0x2c/0x54
> really_probe+0x200/0x2c4
> driver_probe_device+0x5c/0x174
> __driver_attach+0xd8/0xdc
> bus_for_each_dev+0x58/0x7c
> bus_add_driver+0xe4/0x1f0
> driver_register+0x7c/0x110
> mdio_driver_register+0x24/0x58
> do_one_initcall+0x74/0x2e8
> do_init_module+0x60/0x1d0
> load_module+0x1968/0x1ff4
> sys_finit_module+0x8c/0x98
> ret_fast_syscall+0x0/0x28
> 0xbedf2ae8
>
> -> #0 (&chip->reg_lock){+.+.}:
> __mutex_lock+0x50/0x8b8
> mutex_lock_nested+0x1c/0x24
> __setup_irq+0x640/0x704
> request_threaded_irq+0xd0/0x150
> mv88e6xxx_g2_irq_setup+0xcc/0x1b4 [mv88e6xxx]
> mv88e6xxx_probe+0x44c/0x694 [mv88e6xxx]
> mdio_probe+0x2c/0x54
> really_probe+0x200/0x2c4
> driver_probe_device+0x5c/0x174
> __driver_attach+0xd8/0xdc
> bus_for_each_dev+0x58/0x7c
> bus_add_driver+0xe4/0x1f0
> driver_register+0x7c/0x110
> mdio_driver_register+0x24/0x58
> do_one_initcall+0x74/0x2e8
> do_init_module+0x60/0x1d0
> load_module+0x1968/0x1ff4
> sys_finit_module+0x8c/0x98
> ret_fast_syscall+0x0/0x28
> 0xbedf2ae8
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&desc->request_mutex);
> lock(&chip->reg_lock);
> lock(&desc->request_mutex);
> lock(&chip->reg_lock);
>
> &desc->request_mutex refer to two different mutex. #1 is the GPIO for
> the chip interrupt. #2 is the chained interrupt between global 1 and
> global 2.
>
> Add lockdep classes to the GPIO interrupt to avoid this.
>
> Reported-by: Russell King <rmk+ker...@armlinux.org.uk>
> Signed-off-by: Andrew Lunn <and...@lunn.ch>
> ---
>
> Hi Russell
>
> Does this fix it for you on Clearfog?
Yes, that also fixes the problem, but I do think this is just papering
over mv88e6xxx needlessly holding locks when it doesn't need to do so.
>
> drivers/net/dsa/mv88e6xxx/chip.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c
> b/drivers/net/dsa/mv88e6xxx/chip.c
> index 32e7af5caa69..936d53a92144 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -442,12 +442,20 @@ static int mv88e6xxx_g1_irq_setup_common(struct
> mv88e6xxx_chip *chip)
>
> static int mv88e6xxx_g1_irq_setup(struct mv88e6xxx_chip *chip)
> {
> + static struct lock_class_key lock_key;
> + static struct lock_class_key request_key;
> int err;
>
> err = mv88e6xxx_g1_irq_setup_common(chip);
> if (err)
> return err;
>
> + /* These lock classes tells lockdep that global 1 irqs are in
> + * a different category than their parent GPIO, so it won't
> + * report false recursion.
> + */
> + irq_set_lockdep_class(chip->irq, &lock_key, &request_key);
> +
> err = request_threaded_irq(chip->irq, NULL,
> mv88e6xxx_g1_irq_thread_fn,
> IRQF_ONESHOT | IRQF_SHARED,
> --
> 2.20.1
>
>
--
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