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Commit 6029755e authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc: Fix deadlock with multiple calls to smp_send_stop 



smp_send_stop can lock up the IPI path for any subsequent calls,
because the receiving CPUs spin in their handler function. This
started becoming a problem with the addition of an smp_send_stop
call in the reboot path, because panics can reboot after doing
their own smp_send_stop.

The NMI IPI variant was fixed with ac61c115 ("powerpc: Fix
smp_send_stop NMI IPI handling"), which leaves the smp_call_function
variant.

This is fixed by having smp_send_stop only ever do the
smp_call_function once. This is a bit less robust than the NMI IPI
fix, because any other call to smp_call_function after smp_send_stop
could deadlock, but that has always been the case, and it was not
been a problem before.

Fixes: f2748bdf ("powerpc/powernv: Always stop secondaries before reboot/shutdown")
Reported-by: default avatarAbdul Haleem <abdhalee@linux.vnet.ibm.com>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent c0f7f5b6

arch/powerpc/kernel/smp.c

+39 −16
Original line number Diff line number Diff line
@@ -565,17 +565,6 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *)) 
}

#endif



static void stop_this_cpu(void *dummy)

{

	/* Remove this CPU */

	set_cpu_online(smp_processor_id(), false);



	hard_irq_disable();

	spin_begin();

	while (1)

		spin_cpu_relax();

}



#ifdef CONFIG_NMI_IPI

static void nmi_stop_this_cpu(struct pt_regs *regs)

{
@@ -583,23 +572,57 @@ 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.

	 *

	 * IRQs are already hard disabled by the smp_handle_nmi_ipi.

	 */

	nmi_ipi_lock();

	nmi_ipi_busy_count--;

	nmi_ipi_unlock();



	stop_this_cpu(NULL);

	/* Remove this CPU */

	set_cpu_online(smp_processor_id(), false);



	spin_begin();

	while (1)

		spin_cpu_relax();

}

#endif



void smp_send_stop(void)

{

#ifdef CONFIG_NMI_IPI

	smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, nmi_stop_this_cpu, 1000000);

#else

}



#else /* CONFIG_NMI_IPI */



static void stop_this_cpu(void *dummy)

{

	/* Remove this CPU */

	set_cpu_online(smp_processor_id(), false);



	hard_irq_disable();

	spin_begin();

	while (1)

		spin_cpu_relax();

}



void smp_send_stop(void)

{

	static bool stopped = false;



	/*

	 * Prevent waiting on csd lock from a previous smp_send_stop.

	 * This is racy, but in general callers try to do the right

	 * thing and only fire off one smp_send_stop (e.g., see

	 * kernel/panic.c)

	 */

	if (stopped)

		return;



	stopped = true;



	smp_call_function(stop_this_cpu, NULL, 0);

#endif

}

#endif /* CONFIG_NMI_IPI */



struct thread_info *current_set[NR_CPUS];