From: Mathieu Desnoyers Date: Wed, 5 Oct 2016 11:20:32 +0000 (-0400) Subject: Fix: work-around upstream Linux timekeeping bug X-Git-Tag: v2.9.0-rc1~4 X-Git-Url: http://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=a9df1445c3d54e647d9aea248cc1b26bb6f15298 Fix: work-around upstream Linux timekeeping bug Linux commit 27727df240c7 ("Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING"), changed the logic to open-code the timekeeping_get_ns() function, but forgot to include the unit conversion from cycles to nanoseconds, breaking the function's output, which impacts LTTng. The following kernel versions are affected: 4.8, 4.7.4+, 4.4.20+, 4.1.32+ We expect that the upstream fix will reach the master and stable branches timely before the next releases, so we use 4.8.1, 4.7.7, 4.4.24, and 4.1.34 as upper bounds (exclusive). Fall-back to the non-NMI-safe trace clock for those kernel versions. We simply discard events from NMI context with a in_nmi() check, as we did before Linux 3.17. Link: http://lkml.kernel.org/r/1475636148-26539-1-git-send-email-john.stultz@linaro.org Signed-off-by: Mathieu Desnoyers --- diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h index 3e8780da..649c93f3 100644 --- a/wrapper/trace-clock.h +++ b/wrapper/trace-clock.h @@ -47,7 +47,16 @@ extern struct lttng_trace_clock *lttng_trace_clock; -#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) +/* + * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with + * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns(). + * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression". + */ +#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \ + && !LTTNG_KERNEL_RANGE(4,8,0, 4,8,1) \ + && !LTTNG_KERNEL_RANGE(4,7,4, 4,7,7) \ + && !LTTNG_KERNEL_RANGE(4,4,20, 4,4,24) \ + && !LTTNG_KERNEL_RANGE(4,1,32, 4,1,34)) DECLARE_PER_CPU(local_t, lttng_last_tsc);