Re: [PATCH] alpha: marvel: Fix lock ordering in init_io7_irqs()

[Magnus Lindholm]

On Fri, Apr 3, 2026 at 5:04 PM Matt Turner <mattst88@xxxxxxxxx> wrote:
>
> Move irq_set_chip_and_handler() and irq_set_status_flags() calls
> outside the io7->irq_lock raw spinlock.  These functions take
> sparse_irq_lock, which is a mutex, and taking a sleeping lock while
> holding a raw spinlock is invalid.  The raw spinlock only needs to
> protect the hardware CSR accesses.
>
> This fixes the following lockdep splat during boot:
>
>   [ BUG: Invalid wait context ]
>   swapper/0/0 is trying to lock:
>   sparse_irq_lock{....}-{4:4}, at: irq_mark_irq
>   other info that might help us debug this:
>   context-{5:5}
>   1 lock held by swapper/0/0:
>    #0: &io7->irq_lock{....}-{2:2}, at: init_io7_irqs.constprop.0
>
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Matt Turner <mattst88@xxxxxxxxx>
> ---
>  arch/alpha/kernel/sys_marvel.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
>
> diff --git ./arch/alpha/kernel/sys_marvel.c ./arch/alpha/kernel/sys_marvel.c
> index 1f99b03effc2..d0bdd5e6cfd7 100644
> --- ./arch/alpha/kernel/sys_marvel.c
> +++ ./arch/alpha/kernel/sys_marvel.c
> @@ -263,6 +263,18 @@ init_io7_irqs(struct io7 *io7,
>          */
>         printk("  Interrupts reported to CPU at PE %u\n", boot_cpuid);
>
> +       /* Set up the lsi irqs.  */
> +       for (i = 0; i < 128; ++i) {
> +               irq_set_chip_and_handler(base + i, lsi_ops, handle_level_irq);
> +               irq_set_status_flags(i, IRQ_LEVEL);
> +       }
> +
> +       /* Set up the msi irqs.  */
> +       for (i = 128; i < (128 + 512); ++i) {
> +               irq_set_chip_and_handler(base + i, msi_ops, handle_level_irq);
> +               irq_set_status_flags(i, IRQ_LEVEL);
> +       }
> +
>         raw_spin_lock(&io7->irq_lock);
>
>         /* set up the error irqs */
> @@ -272,26 +284,13 @@ init_io7_irqs(struct io7 *io7,
>         io7_redirect_irq(io7, &io7->csrs->STV_CTL.csr, boot_cpuid);
>         io7_redirect_irq(io7, &io7->csrs->HEI_CTL.csr, boot_cpuid);
>
> -       /* Set up the lsi irqs.  */
> -       for (i = 0; i < 128; ++i) {
> -               irq_set_chip_and_handler(base + i, lsi_ops, handle_level_irq);
> -               irq_set_status_flags(i, IRQ_LEVEL);
> -       }
> -
>         /* Disable the implemented irqs in hardware.  */
> -       for (i = 0; i < 0x60; ++i)
> +       for (i = 0; i < 0x60; ++i)
>                 init_one_io7_lsi(io7, i, boot_cpuid);
>
>         init_one_io7_lsi(io7, 0x74, boot_cpuid);
>         init_one_io7_lsi(io7, 0x75, boot_cpuid);
>
> -
> -       /* Set up the msi irqs.  */
> -       for (i = 128; i < (128 + 512); ++i) {
> -               irq_set_chip_and_handler(base + i, msi_ops, handle_level_irq);
> -               irq_set_status_flags(i, IRQ_LEVEL);
> -       }
> -
>         for (i = 0; i < 16; ++i)
>                 init_one_io7_msi(io7, i, boot_cpuid);
>
> --

The lock ordering fix makes sense to me.

One question though: in the moved setup loops we now have

    irq_set_chip_and_handler(base + i, ...)

but still

    irq_set_status_flags(i, IRQ_LEVEL);

Why does irq_set_status_flags() not need `base + i` as
well? I would have expected that to match the IRQ number
passed to irq_set_chip_and_handler(), i.e. use

    irq_set_status_flags(base + i, IRQ_LEVEL);


Magnus