• Nicholas Piggin's avatar
    powerpc: Fix smp_send_stop NMI IPI handling · ac61c115
    Nicholas Piggin authored
    The NMI IPI handler for a receiving CPU increments nmi_ipi_busy_count
    over the handler function call, which causes later smp_send_nmi_ipi()
    callers to spin until the call is finished.
    
    The stop_this_cpu() function never returns, so the busy count is never
    decremeted, which can cause the system to hang in some cases. For
    example panic() will call smp_send_stop() early on which calls
    stop_this_cpu() on other CPUs, then later in the reboot path,
    pnv_restart() will call smp_send_stop() again, which hangs.
    
    Fix this by adding a special case to the stop_this_cpu() handler to
    decrement the busy count, because it will never return.
    
    Now that the NMI/non-NMI versions of stop_this_cpu() are different,
    split them out into separate functions rather than doing #ifdef tricks
    to share the body between the two functions.
    
    Fixes: 6bed3237 ("powerpc: use NMI IPI for smp_send_stop")
    Reported-by: default avatarAbdul Haleem <abdhalee@linux.vnet.ibm.com>
    Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
    [mpe: Split out the functions, tweak change log a bit]
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    ac61c115
smp.c 26.3 KB