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From: John Stultz <john.stultz@linaro.org>
To: lkml <linux-kernel@vger.kernel.org>
Cc: John Stultz <john.stultz@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	stable <stable@vger.kernel.org>
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> (raw)
In-Reply-To: <1471993702-29148-1-git-send-email-john.stultz@linaro.org>

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 <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable <stable@vger.kernel.org> # 4.1+
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 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

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-23 23:08 [GIT PULL][PATCH 0/2] Timekeeping items for 4.8 via tip/timers/urgent John Stultz
2016-08-23 23:08 ` John Stultz [this message]
2016-08-24  7:40   ` [tip:timers/urgent] timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING tip-bot for John Stultz
2016-10-05  0:30   ` [PATCH 1/2] " Alexei Starovoitov
2016-10-05  0:50     ` John Stultz
2016-10-05  2:55     ` [PATCH] timekeeping: Fix __ktime_get_fast_ns() regression John Stultz
2016-10-05 10:57       ` Mathieu Desnoyers
2016-10-05 13:48       ` [tip:timers/urgent] " tip-bot for John Stultz
2016-08-23 23:08 ` [PATCH 2/2] timekeeping: Cap array access in timekeeping_debug to protect against invalid sleep times John Stultz
2016-08-24  0:58   ` Chen Yu
2016-08-24  2:54     ` John Stultz
2016-08-24  2:56   ` [RFC][PATCH v2] " John Stultz
2016-08-24  7:41   ` [tip:timers/urgent] timekeeping: Cap array access in timekeeping_debug tip-bot for John Stultz

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