Fix: lttng trace-clock needs to disable preemption

We use a per-cpu data structure, and some contexts (e.g. buffer create)
call this function with preemption enabled. This is the case also for
buffer flush operation.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index d2b7f19dba76e197738d055217250d38767bd816..d6439c7fb13bb1249560e1351cf649a94056414f 100644 (file)
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -93,7 +93,7 @@ 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)
 {
@@ -102,6 +102,7 @@ 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);
        /*
@@ -115,6 +116,7 @@ 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;