• Vineet Gupta's avatar
    ARCv2: SMP: Emulate IPI to self using software triggered interrupt · bb143f81
    Vineet Gupta authored
    ARConnect/MCIP Inter-Core-Interrupt module can't send interrupt to
    local core. So use core intc capability to trigger software
    interrupt to self, using an unsued IRQ #21.
    
    This showed up as csd deadlock with LTP trace_sched on a dual core
    system. This test acts as scheduler fuzzer, triggering all sorts of
    schedulting activity. Trouble starts with IPI to self, which doesn't get
    delivered (effectively lost due to H/w capability), but the msg intended
    to be sent remain enqueued in per-cpu @ipi_data.
    
    All subsequent IPIs to this core from other cores get elided due to the
    IPI coalescing optimization in ipi_send_msg_one() where a pending msg
    implies an IPI already sent and assumes other core is yet to ack it.
    After the elided IPI, other core simply goes into csd_lock_wait()
    but never comes out as this core never sees the interrupt.
    
    Fixes STAR 9001008624
    
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: <stable@vger.kernel.org>        [4.2]
    Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
    bb143f81
entry-arcv2.S 6.57 KB