Fix: show warning for broken clock work-around

[lttng-modules.git] / wrapper / trace-clock.h

diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index d7d18429ba1c1f17d22d35c4ce6ec8484aef422e..05472dc1cebcb341970e2f659ca64f1cefc058fa 100644 (file)
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -39,12 +39,25 @@
 #include "percpu-defs.h"
 #include "random.h"
 
-#if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,7,0, 3,10,14,0,0)) \
+#if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,123,0,0, 3,10,14,0,0,0)) \
        || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3))
 #error "Linux kernels 3.10 and 3.11 introduce a deadlock in the timekeeping subsystem. Fixed by commit 7bd36014460f793c19e7d6c94dab67b0afcfcb7f \"timekeeping: Fix HRTICK related deadlock from ntp lock changes\" in Linux."
 #endif
 
-#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 (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))
+#define LTTNG_CLOCK_NMI_SAFE_BROKEN
+#endif
+
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
+       && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
 
 DECLARE_PER_CPU(local_t, lttng_last_tsc);
 
@@ -90,7 +103,7 @@ static inline u64 trace_clock_fixup(u64 src_now, u64 last)
 #endif /* #else #if (BITS_PER_LONG == 32) */
 
 /*
- * Always called with preemption disabled. Can be interrupted.
+ * Sometimes called with preemption enabled. Can be interrupted.
  */
 static inline u64 trace_clock_monotonic_wrapper(void)
 {
@@ -99,6 +112,7 @@ static inline u64 trace_clock_monotonic_wrapper(void)
        local_t *last_tsc;
 
        /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
+       preempt_disable();
        last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
        last = local_read(last_tsc);
        /*
@@ -112,6 +126,7 @@ static inline u64 trace_clock_monotonic_wrapper(void)
        if (((long) now - (long) last) < 0)
                now = trace_clock_fixup(now, last);
        result = local_cmpxchg(last_tsc, last, (unsigned long) now);
+       preempt_enable();
        if (result == last) {
                /* Update done. */
                return now;