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authorJohn Stultz <john.stultz@linaro.org>2016-10-04 19:55:48 -0700
committerThomas Gleixner <tglx@linutronix.de>2016-10-05 15:44:46 +0200
commit58bfea9532552d422bde7afa207e1a0f08dffa7d (patch)
tree9635381af9572968f1ce94dd5b7152f114908680 /kernel
parent597f03f9d133e9837d00965016170271d4f87dcf (diff)
downloadlinux-58bfea9532552d422bde7afa207e1a0f08dffa7d.tar.bz2
timekeeping: Fix __ktime_get_fast_ns() regression
In commit 27727df240c7 ("Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING"), I changed the logic to open-code the timekeeping_get_ns() function, but I forgot to include the unit conversion from cycles to nanoseconds, breaking the function's output, which impacts users like perf. This results in bogus perf timestamps like: swapper 0 [000] 253.427536: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.426573: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.426687: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.426800: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.426905: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.427022: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.427127: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.427239: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.427346: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 254.427463: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 255.426572: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) Instead of more reasonable expected timestamps like: swapper 0 [000] 39.953768: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.064839: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.175956: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.287103: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.398217: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.509324: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.620437: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.731546: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.842654: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 40.953772: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) swapper 0 [000] 41.064881: 111111111 cpu-clock: ffffffff810a0de6 native_safe_halt+0x6 ([kernel.kallsyms]) Add the proper use of timekeeping_delta_to_ns() to convert the cycle delta to nanoseconds as needed. Thanks to Brendan and Alexei for finding this quickly after the v4.8 release. Unfortunately the problematic commit has landed in some -stable trees so they'll need this fix as well. Many apologies for this mistake. I'll be looking to add a perf-clock sanity test to the kselftest timers tests soon. Fixes: 27727df240c7 "timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING" Reported-by: Brendan Gregg <bgregg@netflix.com> Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> Tested-and-reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: stable <stable@vger.kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/1475636148-26539-1-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/timekeeping.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e07fb093f819..37dec7e3db43 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -403,8 +403,11 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
tkr = tkf->base + (seq & 0x01);
now = ktime_to_ns(tkr->base);
- now += clocksource_delta(tkr->read(tkr->clock),
- tkr->cycle_last, tkr->mask);
+ now += timekeeping_delta_to_ns(tkr,
+ clocksource_delta(
+ tkr->read(tkr->clock),
+ tkr->cycle_last,
+ tkr->mask));
} while (read_seqcount_retry(&tkf->seq, seq));
return now;