4.7-stable review patch. If anyone has any objections, please let me know.
------------------ From: John Stultz <[email protected]> commit 58bfea9532552d422bde7afa207e1a0f08dffa7d upstream. 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 <[email protected]> Reported-by: Alexei Starovoitov <[email protected]> Tested-and-reviewed-by: Mathieu Desnoyers <[email protected]> Signed-off-by: John Stultz <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Steven Rostedt <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Thomas Gleixner <[email protected]> Cc: Mathieu Desnoyers <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- kernel/time/timekeeping.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -403,8 +403,11 @@ static __always_inline u64 __ktime_get_f 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;
