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Commit 5b73151f authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
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powerpc: NMI IPI make NMI IPIs fully sychronous 



There is an asynchronous aspect to smp_send_nmi_ipi. The caller waits
for all CPUs to call in to the handler, but it does not wait for
completion of the handler. This is a needless complication, so remove
it and always wait synchronously.

The synchronous wait allows the caller to easily time out and clear
the wait for completion (zero nmi_ipi_busy_count) in the case of badly
behaved handlers. This would have prevented the recent smp_send_stop
NMI IPI bug from causing the system to hang.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 9b81c021

arch/powerpc/include/asm/smp.h

+0 −1
Original line number Diff line number Diff line
@@ -56,7 +56,6 @@ struct smp_ops_t { 
	int   (*cpu_bootable)(unsigned int nr);

};



extern void smp_flush_nmi_ipi(u64 delay_us);

extern int smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);

extern int smp_send_safe_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us);

extern void smp_send_debugger_break(void);

arch/powerpc/kernel/smp.c

+27 −23
Original line number Diff line number Diff line
@@ -423,6 +423,7 @@ int smp_handle_nmi_ipi(struct pt_regs *regs) 
	fn(regs);



	nmi_ipi_lock();

	if (nmi_ipi_busy_count > 1) /* Can race with caller time-out */

		nmi_ipi_busy_count--;

out:

	nmi_ipi_unlock_end(&flags);
@@ -448,29 +449,11 @@ static void do_smp_send_nmi_ipi(int cpu, bool safe) 
	}

}



void smp_flush_nmi_ipi(u64 delay_us)

{

	unsigned long flags;



	nmi_ipi_lock_start(&flags);

	while (nmi_ipi_busy_count) {

		nmi_ipi_unlock_end(&flags);

		udelay(1);

		if (delay_us) {

			delay_us--;

			if (!delay_us)

				return;

		}

		nmi_ipi_lock_start(&flags);

	}

	nmi_ipi_unlock_end(&flags);

}



/*

 * - cpu is the target CPU (must not be this CPU), or NMI_IPI_ALL_OTHERS.

 * - fn is the target callback function.

 * - delay_us > 0 is the delay before giving up waiting for targets to

 *   enter the handler, == 0 specifies indefinite delay.

 *   complete executing the handler, == 0 specifies indefinite delay.

 */

int __smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us, bool safe)

{
@@ -507,8 +490,12 @@ int __smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us, bool 


	do_smp_send_nmi_ipi(cpu, safe);



	nmi_ipi_lock();

	/* nmi_ipi_busy_count is held here, so unlock/lock is okay */

	while (!cpumask_empty(&nmi_ipi_pending_mask)) {

		nmi_ipi_unlock();

		udelay(1);

		nmi_ipi_lock();

		if (delay_us) {

			delay_us--;

			if (!delay_us)
@@ -516,12 +503,28 @@ int __smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us, bool 
		}

	}



	while (nmi_ipi_busy_count > 1) {

		nmi_ipi_unlock();

		udelay(1);

		nmi_ipi_lock();

		if (delay_us) {

			delay_us--;

			if (!delay_us)

				break;

		}

	}



	if (!cpumask_empty(&nmi_ipi_pending_mask)) {

		/* Could not gather all CPUs */

		/* Timeout waiting for CPUs to call smp_handle_nmi_ipi */

		ret = 0;

		cpumask_clear(&nmi_ipi_pending_mask);

	}

	if (nmi_ipi_busy_count > 1) {

		/* Timeout waiting for CPUs to execute fn */

		ret = 0;

		nmi_ipi_busy_count = 1;

	}



	nmi_ipi_busy_count--;

	nmi_ipi_unlock_end(&flags);
@@ -597,6 +600,7 @@ static void nmi_stop_this_cpu(struct pt_regs *regs) 
	 * IRQs are already hard disabled by the smp_handle_nmi_ipi.

	 */

	nmi_ipi_lock();

	if (nmi_ipi_busy_count > 1)

		nmi_ipi_busy_count--;

	nmi_ipi_unlock();

arch/powerpc/kernel/watchdog.c

+0 −1
Original line number Diff line number Diff line
@@ -174,7 +174,6 @@ static void watchdog_smp_panic(int cpu, u64 tb) 
				continue;

			smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);

		}

		smp_flush_nmi_ipi(1000000);

	}



	/* Take the stuck CPUs out of the watch group */