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Commit 27727df2 authored by John Stultz's avatar John Stultz Committed by Thomas Gleixner
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timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING 



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.

Fixes: 4ca22c26 "timekeeping: Add warnings when overflows or underflows are observed"
Reported-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Reported-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
Cc: stable <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/1471993702-29148-2-git-send-email-john.stultz@linaro.org


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent fa8410b3

kernel/time/timekeeping.c

+4 −1
Original line number Diff line number Diff line
@@ -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;