From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x241.google.com (mail-pg0-x241.google.com [IPv6:2607:f8b0:400e:c05::241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40W3l44pHQzF24L for ; Wed, 25 Apr 2018 12:18:07 +1000 (AEST) Received: by mail-pg0-x241.google.com with SMTP id e9so12219585pgr.7 for ; Tue, 24 Apr 2018 19:18:07 -0700 (PDT) From: Nicholas Piggin To: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin , Abdul Haleem Subject: [PATCH] powerpc: Fix smp_send_stop NMI IPI handling Date: Wed, 25 Apr 2018 12:17:53 +1000 Message-Id: <20180425021753.26275-1-npiggin@gmail.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Signed-off-by: Nicholas Piggin --- arch/powerpc/kernel/smp.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index e16ec7b3b427..250fccf04c6e 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c @@ -567,10 +567,19 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *)) #ifdef CONFIG_NMI_IPI static void 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(); #else static void stop_this_cpu(void *dummy) -#endif { +#endif /* Remove this CPU */ set_cpu_online(smp_processor_id(), false); -- 2.17.0