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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: 4ca22c2648 "timekeeping: Add warnings when overflows or underflows are observed"
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
John Stultz 2016-08-23 16:08:21 -07:00 committed by Thomas Gleixner
parent fa8410b355
commit 27727df240
1 changed files with 4 additions and 1 deletions
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5
kernel/time/timekeeping.c
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@ -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;