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powerpc: NMI IPI make NMI IPIs fully sychronous

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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: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2018-04-25 15:17:59 +10:00 committed by Michael Ellerman
parent 9b81c0211c
commit 5b73151fff
3 changed files with 27 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/powerpc/include/asm/smp.h
View File

@ -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);

50
arch/powerpc/kernel/smp.c
View File

@ -423,7 +423,8 @@ int smp_handle_nmi_ipi(struct pt_regs *regs)
fn(regs);
nmi_ipi_lock();
nmi_ipi_busy_count--;
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 +490,23 @@ 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)
break;
}
}
while (nmi_ipi_busy_count > 1) {
nmi_ipi_unlock();
udelay(1);
nmi_ipi_lock();
if (delay_us) {
delay_us--;
if (!delay_us)
@ -516,12 +514,17 @@ int __smp_send_nmi_ipi(int cpu, void (*fn)(struct pt_regs *), u64 delay_us, bool
}
}
nmi_ipi_lock();
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);
@ -597,7 +600,8 @@ static void nmi_stop_this_cpu(struct pt_regs *regs)
* IRQs are already hard disabled by the smp_handle_nmi_ipi.
*/
nmi_ipi_lock();
nmi_ipi_busy_count--;
if (nmi_ipi_busy_count > 1)
nmi_ipi_busy_count--;
nmi_ipi_unlock();
spin_begin();

1
arch/powerpc/kernel/watchdog.c
View File

@ -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 */