From 2c44512a8bb58e1b566c285137c0c38dfa26278f Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Thu, 14 Feb 2019 16:39:57 -0500 Subject: [PATCH] Fix: additional compiler barriers for procname context Use additional volatile load/stores and compiler barriers to make sure the compiler do not reorder the nesting counter wrt procname cache content load/stores. Signed-off-by: Mathieu Desnoyers --- liblttng-ust/lttng-context-procname.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/liblttng-ust/lttng-context-procname.c b/liblttng-ust/lttng-context-procname.c index 95d5f28d..8c1520ad 100644 --- a/liblttng-ust/lttng-context-procname.c +++ b/liblttng-ust/lttng-context-procname.c @@ -49,24 +49,29 @@ static DEFINE_URCU_TLS(int, procname_nesting); static inline char *wrapper_getprocname(void) { - int nesting = URCU_TLS(procname_nesting); + int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting)); if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX)) return ""; if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) { CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1); + /* Increment nesting before updating cache. */ + cmm_barrier(); lttng_ust_getprocname(URCU_TLS(cached_procname)[nesting]); URCU_TLS(cached_procname)[nesting][LTTNG_UST_PROCNAME_LEN - 1] = '\0'; + /* Decrement nesting after updating cache. */ + cmm_barrier(); CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting); } return URCU_TLS(cached_procname)[nesting]; } +/* Reset should not be called from a signal handler. */ void lttng_context_procname_reset(void) { - URCU_TLS(cached_procname)[1][0] = '\0'; + CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0'); CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1); - URCU_TLS(cached_procname)[0][0] = '\0'; + CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0'); CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0); } -- 2.34.1