On Wed, Dec 09, 2020 at 07:54:26PM +0100, Thomas Gleixner wrote:
> On Wed, Dec 09 2020 at 18:15, Mark Rutland wrote:
> > In arch/x86/kernel/apic/io_apic.c's timer_irq_works() we do:
> >
> > local_irq_save(flags);
> > local_irq_enable();
> >
> > [ trigger an IRQ here ]
> >
> > local_irq_restore(flags);
> >
> > ... and in check_timer() we call that a number of times after either a
> > local_irq_save() or local_irq_disable(), eventually trailing with a
> > local_irq_disable() that will balance things up before calling
> > local_irq_restore().
I gave the patchlet below a spin with my debug patch, and it boots
cleanly for me under QEMU. If you spin it as a real patch, feel free to
add:
Tested-by: Mark Rutland <mark.rutland@xxxxxxx>
Mark.
> ---
> arch/x86/kernel/apic/io_apic.c | 22 ++++++----------------
> 1 file changed, 6 insertions(+), 16 deletions(-)
>
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -1618,21 +1618,16 @@ static void __init delay_without_tsc(voi
> static int __init timer_irq_works(void)
> {
> unsigned long t1 = jiffies;
> - unsigned long flags;
>
> if (no_timer_check)
> return 1;
>
> - local_save_flags(flags);
> local_irq_enable();
> -
> if (boot_cpu_has(X86_FEATURE_TSC))
> delay_with_tsc();
> else
> delay_without_tsc();
>
> - local_irq_restore(flags);
> -
> /*
> * Expect a few ticks at least, to be sure some possible
> * glue logic does not lock up after one or two first
> @@ -1641,10 +1636,10 @@ static int __init timer_irq_works(void)
> * least one tick may be lost due to delays.
> */
>
> - /* jiffies wrap? */
> - if (time_after(jiffies, t1 + 4))
> - return 1;
> - return 0;
> + local_irq_disable();
> +
> + /* Did jiffies advance? */
> + return time_after(jiffies, t1 + 4);
> }
>
> /*
> @@ -2117,13 +2112,12 @@ static inline void __init check_timer(vo
> struct irq_cfg *cfg = irqd_cfg(irq_data);
> int node = cpu_to_node(0);
> int apic1, pin1, apic2, pin2;
> - unsigned long flags;
> int no_pin1 = 0;
>
> if (!global_clock_event)
> return;
>
> - local_irq_save(flags);
> + local_irq_disable();
>
> /*
> * get/set the timer IRQ vector:
> @@ -2191,7 +2185,6 @@ static inline void __init check_timer(vo
> goto out;
> }
> panic_if_irq_remap("timer doesn't work through Interrupt-remapped IO-APIC");
> - local_irq_disable();
> clear_IO_APIC_pin(apic1, pin1);
> if (!no_pin1)
> apic_printk(APIC_QUIET, KERN_ERR "..MP-BIOS bug: "
> @@ -2215,7 +2208,6 @@ static inline void __init check_timer(vo
> /*
> * Cleanup, just in case ...
> */
> - local_irq_disable();
> legacy_pic->mask(0);
> clear_IO_APIC_pin(apic2, pin2);
> apic_printk(APIC_QUIET, KERN_INFO "....... failed.\n");
> @@ -2232,7 +2224,6 @@ static inline void __init check_timer(vo
> apic_printk(APIC_QUIET, KERN_INFO "..... works.\n");
> goto out;
> }
> - local_irq_disable();
> legacy_pic->mask(0);
> apic_write(APIC_LVT0, APIC_LVT_MASKED | APIC_DM_FIXED | cfg->vector);
> apic_printk(APIC_QUIET, KERN_INFO "..... failed.\n");
> @@ -2251,7 +2242,6 @@ static inline void __init check_timer(vo
> apic_printk(APIC_QUIET, KERN_INFO "..... works.\n");
> goto out;
> }
> - local_irq_disable();
> apic_printk(APIC_QUIET, KERN_INFO "..... failed :(.\n");
> if (apic_is_x2apic_enabled())
> apic_printk(APIC_QUIET, KERN_INFO
> @@ -2260,7 +2250,7 @@ static inline void __init check_timer(vo
> panic("IO-APIC + timer doesn't work! Boot with apic=debug and send a "
> "report. Then try booting with the 'noapic' option.\n");
> out:
> - local_irq_restore(flags);
> + local_irq_enable();
> }
>
> /*
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