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    Subject[PATCH] x86 apic: Ack all pending irqs when crashed/on kexec - V4
    Date
    From: Kerstin Jonsson <kerstin.jonsson@ericsson.com>

    When the SMP kernel decides to crash_kexec() the local APICs may have
    pending interrupts in their vector tables.
    The setup routine for the local APIC has a deficient mechanism for
    clearing these interrupts, it only handles interrupts that has already
    been dispatched to the local core for servicing (the ISR register)
    safely, it doesn't consider lower prioritized queued interrupts stored
    in the IRR register.

    If you have more than one pending interrupt within the same 32 bit word
    in the LAPIC vector table registers you may find yourself entering the
    IO APIC setup with pending interrupts left in the LAPIC. This is a
    situation for wich the IO APIC setup is not prepared. Depending of
    what/which interrupt vector/vectors are stuck in the APIC tables your
    system may show various degrees of malfunctioning.
    That was the reason why the check_timer() failed in our system, the
    timer interrupts was blocked by pending interrupts from the old kernel
    when routed trough the IO APIC.

    Additional comment from Jiri Bohac:
    ==============
    If this should go into stable release,
    I'd add some kind of limit on the number of iterations, just to be safe from
    hard to debug lock-ups:

    +if (loops++ > MAX_LOOPS) {
    + printk("LAPIC pending clean-up")
    + break;
    +}
    while (queued);

    with MAX_LOOPS something like 1E9 this would leave plenty of time for the
    pending IRQs to be cleared and would and still cause at most a second of delay
    if the loop were to lock-up for whatever reason.
    ==============

    From trenn@suse.de:
    V2: Use tsc if avail to bail out after 1 sec due to possible virtual apic_read
    calls which may take rather long (suggested by: Avi Kivity <avi@redhat.com>)
    If no tsc is available bail out quickly after cpu_khz, if we broke out too
    early and still have irqs pending (which should never happen?) we still
    get a WARN_ON...

    V3: - Fixed indentation -> checkpatch clean
    - max_loops must be signed

    V4: - Fix typo, mixed up tsc and ntsc in first rdtscll() call

    CC: jbohac@novell.com
    CC: "Yinghai Lu" <yinghai@kernel.org>
    CC: akpm@linux-foundation.org
    CC: mingo@elte.hu
    CC: "Kerstin Jonsson" <kerstin.jonsson@ericsson.com>
    CC: "Avi Kivity" <avi@redhat.com>
    Signed-off-by: Thomas Renninger <trenn@suse.de>
    ---
    arch/x86/kernel/apic/apic.c | 41 +++++++++++++++++++++++++++++++++--------
    1 files changed, 33 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    index 3987e44..414a5df 100644
    --- a/arch/x86/kernel/apic/apic.c
    +++ b/arch/x86/kernel/apic/apic.c
    @@ -51,6 +51,7 @@
    #include <asm/smp.h>
    #include <asm/mce.h>
    #include <asm/kvm_para.h>
    +#include <asm/tsc.h>

    unsigned int num_processors;

    @@ -1151,8 +1152,13 @@ static void __cpuinit lapic_setup_esr(void)
    */
    void __cpuinit setup_local_APIC(void)
    {
    - unsigned int value;
    - int i, j;
    + unsigned int value, queued;
    + int i, j, acked = 0;
    + unsigned long long tsc = 0, ntsc;
    + long long max_loops = cpu_khz;
    +
    + if (cpu_has_tsc)
    + rdtscll(tsc);

    if (disable_apic) {
    arch_disable_smp_support();
    @@ -1204,13 +1210,32 @@ void __cpuinit setup_local_APIC(void)
    * the interrupt. Hence a vector might get locked. It was noticed
    * for timer irq (vector 0x31). Issue an extra EOI to clear ISR.
    */
    - for (i = APIC_ISR_NR - 1; i >= 0; i--) {
    - value = apic_read(APIC_ISR + i*0x10);
    - for (j = 31; j >= 0; j--) {
    - if (value & (1<<j))
    - ack_APIC_irq();
    + do {
    + queued = 0;
    + for (i = APIC_ISR_NR - 1; i >= 0; i--)
    + queued |= apic_read(APIC_IRR + i*0x10);
    +
    + for (i = APIC_ISR_NR - 1; i >= 0; i--) {
    + value = apic_read(APIC_ISR + i*0x10);
    + for (j = 31; j >= 0; j--) {
    + if (value & (1<<j)) {
    + ack_APIC_irq();
    + acked++;
    + }
    + }
    }
    - }
    + if (acked > 256) {
    + printk(KERN_ERR "LAPIC pending interrupts after %d EOI\n",
    + acked);
    + break;
    + }
    + if (cpu_has_tsc) {
    + rdtscll(ntsc);
    + max_loops = (cpu_khz << 10) - (ntsc - tsc);
    + } else
    + max_loops--;
    + } while (queued && max_loops > 0);
    + WARN_ON(!max_loops);

    /*
    * Now that we are all set up, enable the APIC
    --
    1.6.3


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