[PATCH v2] powerpc: Fix smp_send_stop NMI IPI handling
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2018-04-25 11:35:24
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
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 smp_send_stop 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, 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 smp_send_stop handler to
decrement the busy count, because it will never return.
Fixes: 6bed3237624e3 ("powerpc: use NMI IPI for smp_send_stop")
Reported-by: Abdul Haleem <redacted>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
Changes since v1:
- Reduce #ifdef spaghetti suggested by mpe
arch/powerpc/kernel/smp.c | 36 +++++++++++++++++++++++++++++-------
1 file changed, 29 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index e16ec7b3b427..41d42c2f88d4 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c@@ -566,10 +566,35 @@ 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 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(); + + /* Remove this CPU */ + set_cpu_online(smp_processor_id(), false); + + spin_begin(); + while (1) + spin_cpu_relax(); +} + +void smp_send_stop(void) +{ + smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, nmi_stop_this_cpu, 1000000); +} + +#else /* CONFIG_NMI_IPI */ + static void stop_this_cpu(void *dummy) -#endif { /* Remove this CPU */ set_cpu_online(smp_processor_id(), false);
@@ -582,12 +607,9 @@ static void stop_this_cpu(void *dummy) void smp_send_stop(void) { -#ifdef CONFIG_NMI_IPI - smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, stop_this_cpu, 1000000); -#else smp_call_function(stop_this_cpu, NULL, 0); -#endif } +#endif /* CONFIG_NMI_IPI */ struct thread_info *current_set[NR_CPUS];
--
2.17.0