ARCv2: SMP: Emulate IPI to self using software triggered interrupt
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: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/kernel/entry-arcv2.S b/arch/arc/kernel/entry-arcv2.S
index b178302..c126460 100644
--- a/arch/arc/kernel/entry-arcv2.S
+++ b/arch/arc/kernel/entry-arcv2.S
@@ -45,11 +45,12 @@
VECTOR handle_interrupt ; (16) Timer0
VECTOR handle_interrupt ; unused (Timer1)
VECTOR handle_interrupt ; unused (WDT)
-VECTOR handle_interrupt ; (19) ICI (inter core interrupt)
-VECTOR handle_interrupt
-VECTOR handle_interrupt
-VECTOR handle_interrupt
-VECTOR handle_interrupt ; (23) End of fixed IRQs
+VECTOR handle_interrupt ; (19) Inter core Interrupt (IPI)
+VECTOR handle_interrupt ; (20) perf Interrupt
+VECTOR handle_interrupt ; (21) Software Triggered Intr (Self IPI)
+VECTOR handle_interrupt ; unused
+VECTOR handle_interrupt ; (23) unused
+# End of fixed IRQs
.rept CONFIG_ARC_NUMBER_OF_INTERRUPTS - 8
VECTOR handle_interrupt
