Commit ac61c115 authored Apr 25, 2018 by Nicholas Piggin Committed by Michael Ellerman Apr 25, 2018

powerpc: Fix smp_send_stop NMI IPI handling



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: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Split out the functions, tweak change log a bit]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent 682e6b4d

arch/powerpc/kernel/smp.c

+17 −5

Original line number	Diff line number	Diff line
		@@ -565,11 +565,7 @@ void crash_send_ipi(void (crash_ipi_callback)(struct pt_regs ))
		}
		#endif

		#ifdef CONFIG_NMI_IPI
		static void stop_this_cpu(struct pt_regs *regs)
		#else
		static void stop_this_cpu(void *dummy)
		#endif
		{
		/* Remove this CPU */
		set_cpu_online(smp_processor_id(), false);
		@@ -580,10 +576,26 @@ static void stop_this_cpu(void *dummy)
		spin_cpu_relax();
		}

		#ifdef CONFIG_NMI_IPI
		static void nmi_stop_this_cpu(struct pt_regs *regs)
		{
		/*
		* This is a special case because it never returns, so the NMI IPI
		* handling would never mark it as done, which makes any later
		* smp_send_nmi_ipi() call spin forever. Mark it done now.
		*/
		nmi_ipi_lock();
		nmi_ipi_busy_count--;
		nmi_ipi_unlock();

		stop_this_cpu(NULL);
		}
		#endif

		void smp_send_stop(void)
		{
		#ifdef CONFIG_NMI_IPI
		smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, stop_this_cpu, 1000000);
		smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, nmi_stop_this_cpu, 1000000);
		#else
		smp_call_function(stop_this_cpu, NULL, 0);
		#endif

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