• Suresh Siddha's avatar
    x86, irq: Allow 0xff for /proc/irq/[n]/smp_affinity on an 8-cpu system · 18374d89
    Suresh Siddha authored
    John Blackwood reported:
    > on an older Dell PowerEdge 6650 system with 8 cpus (4 are hyper-threaded),
    > and  32 bit (x86) kernel, once you change the irq smp_affinity of an irq
    > to be less than all cpus in the system, you can never change really the
    > irq smp_affinity back to be all cpus in the system (0xff) again,
    > even though no error status is returned on the "/bin/echo ff >
    > /proc/irq/[n]/smp_affinity" operation.
    >
    > This is due to that fact that BAD_APICID has the same value as
    > all cpus (0xff) on 32bit kernels, and thus the value returned from
    > set_desc_affinity() via the cpu_mask_to_apicid_and() function is treated
    > as a failure in set_ioapic_affinity_irq_desc(), and no affinity changes
    > are made.
    
    set_desc_affinity() is already checking if the incoming cpu mask
    intersects with the cpu online mask or not. So there is no need
    for the apic op cpu_mask_to_apicid_and() to check again
    and return BAD_APICID.
    
    Remove the BAD_APICID return value from cpu_mask_to_apicid_and()
    and also fix set_desc_affinity() to return -1 instead of using BAD_APICID
    to represent error conditions (as cpu_mask_to_apicid_and() can return
    logical or physical apicid values and BAD_APICID is really to represent
    bad physical apic id).
    Reported-by: default avatarJohn Blackwood <john.blackwood@ccur.com>
    Root-caused-by: default avatarJohn Blackwood <john.blackwood@ccur.com>
    Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
    LKML-Reference: <1261103386.2535.409.camel@sbs-t61>
    Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
    18374d89
bigsmp_32.c 6.1 KB