• Will Deacon's avatar
    ARM: 6194/1: change definition of cpu_relax() for ARM11MPCore · 534be1d5
    Will Deacon authored
    Linux expects that if a CPU modifies a memory location, then that
    modification will eventually become visible to other CPUs in the system.
    
    On an ARM11MPCore processor, loads are prioritised over stores so it is
    possible for a store operation to be postponed if a polling loop immediately
    follows it. If the variable being polled indirectly depends on the outstanding
    store [for example, another CPU may be polling the variable that is pending
    modification] then there is the potential for deadlock if interrupts are
    disabled. This deadlock occurs in the KGDB testsuire when executing on an
    SMP ARM11MPCore configuration.
    
    This patch changes the definition of cpu_relax() to smp_mb() for ARMv6 cores,
    forcing a flushing of the write buffer on SMP systems before the next load
    takes place. If the Kernel is not compiled for SMP support, this will expand
    to a barrier() as before.
    Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    534be1d5
processor.h 3.01 KB