This is a note to let you know that I've just added the patch titled x86/i8259: Mark legacy PIC interrupts with IRQ_LEVEL to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-i8259-mark-legacy-pic-interrupts-with-irq_level.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 5fa55950729d0762a787451dc52862c3f850f859 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Date: Mon, 9 Jan 2023 22:57:13 +0100 Subject: x86/i8259: Mark legacy PIC interrupts with IRQ_LEVEL From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> commit 5fa55950729d0762a787451dc52862c3f850f859 upstream. Baoquan reported that after triggering a crash the subsequent crash-kernel fails to boot about half of the time. It triggers a NULL pointer dereference in the periodic tick code. This happens because the legacy timer interrupt (IRQ0) is resent in software which happens in soft interrupt (tasklet) context. In this context get_irq_regs() returns NULL which leads to the NULL pointer dereference. The reason for the resend is a spurious APIC interrupt on the IRQ0 vector which is captured and leads to a resend when the legacy timer interrupt is enabled. This is wrong because the legacy PIC interrupts are level triggered and therefore should never be resent in software, but nothing ever sets the IRQ_LEVEL flag on those interrupts, so the core code does not know about their trigger type. Ensure that IRQ_LEVEL is set when the legacy PCI interrupts are set up. Fixes: a4633adcdbc1 ("[PATCH] genirq: add genirq sw IRQ-retrigger") Reported-by: Baoquan He <bhe@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Baoquan He <bhe@xxxxxxxxxx> Link: https://lore.kernel.org/r/87mt6rjrra.ffs@tglx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/i8259.c | 1 + arch/x86/kernel/irqinit.c | 4 +++- 2 files changed, 4 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/i8259.c +++ b/arch/x86/kernel/i8259.c @@ -114,6 +114,7 @@ static void make_8259A_irq(unsigned int disable_irq_nosync(irq); io_apic_irqs &= ~(1<<irq); irq_set_chip_and_handler(irq, &i8259A_chip, handle_level_irq); + irq_set_status_flags(irq, IRQ_LEVEL); enable_irq(irq); lapic_assign_legacy_vector(irq, true); } --- a/arch/x86/kernel/irqinit.c +++ b/arch/x86/kernel/irqinit.c @@ -72,8 +72,10 @@ void __init init_ISA_irqs(void) legacy_pic->init(0); - for (i = 0; i < nr_legacy_irqs(); i++) + for (i = 0; i < nr_legacy_irqs(); i++) { irq_set_chip_and_handler(i, chip, handle_level_irq); + irq_set_status_flags(i, IRQ_LEVEL); + } } void __init init_IRQ(void) Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are queue-4.19/x86-i8259-mark-legacy-pic-interrupts-with-irq_level.patch