From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f175.google.com ([209.85.192.175]:33493 "EHLO mail-pf0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754469AbcHWXI3 (ORCPT ); Tue, 23 Aug 2016 19:08:29 -0400 Received: by mail-pf0-f175.google.com with SMTP id y134so47995720pfg.0 for ; Tue, 23 Aug 2016 16:08:29 -0700 (PDT) From: John Stultz To: lkml Cc: John Stultz , Steven Rostedt , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , stable Subject: [PATCH 1/2] timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING Date: Tue, 23 Aug 2016 16:08:21 -0700 Message-Id: <1471993702-29148-2-git-send-email-john.stultz@linaro.org> In-Reply-To: <1471993702-29148-1-git-send-email-john.stultz@linaro.org> References: <1471993702-29148-1-git-send-email-john.stultz@linaro.org> Sender: stable-owner@vger.kernel.org List-ID: When I added some extra sanity checking in timekeeping_get_ns() under CONFIG_DEBUG_TIMEKEEPING, I missed that the NMI safe __ktime_get_fast_ns() method was using timekeeping_get_ns(). Thus the locking added to the debug checks broke the NMI-safety of __ktime_get_fast_ns(). This patch open-codes the timekeeping_get_ns() logic for __ktime_get_fast_ns(), so can avoid any deadlocks in NMI. Cc: Steven Rostedt Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Thomas Gleixner Cc: stable # 4.1+ Reported-by: Steven Rostedt Reported-by: Peter Zijlstra Signed-off-by: John Stultz --- kernel/time/timekeeping.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 3b65746..e07fb09 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -401,7 +401,10 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) do { seq = raw_read_seqcount_latch(&tkf->seq); tkr = tkf->base + (seq & 0x01); - now = ktime_to_ns(tkr->base) + timekeeping_get_ns(tkr); + now = ktime_to_ns(tkr->base); + + now += clocksource_delta(tkr->read(tkr->clock), + tkr->cycle_last, tkr->mask); } while (read_seqcount_retry(&tkf->seq, seq)); return now; -- 1.9.1