timer: add limitation note for sync stop and reset

If a timer's callback function calls rte_timer_reset_sync() or
rte_timer_stop_sync() on another timer that is in the RUNNING state and
owned by the current lcore, the *_sync() calls will loop indefinitely.

Relatedly, if a timer's callback function calls *_sync() on another
timer that is in the RUNNING state and is owned by a different lcore,
but a timer callback function runs on that different lcore and calls
*_sync() on a timer that is in the RUNNING state and owned by the
current lcore, the two lcores will loop indefinitely.

Add a note in the rte_timer_stop_sync and rte_timer_reset_sync
documentation that indicates that these APIs should not be used inside
timer callback functions in order to avoid the hangs described above,
and suggests an alternative.

Bugzilla ID: 491
Cc: stable@dpdk.org
Signed-off-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

diff --git a/lib/librte_timer/rte_timer.h b/lib/librte_timer/rte_timer.h
index 7af8378..22a27aa 100644 (file)
--- a/lib/librte_timer/rte_timer.h
+++ b/lib/librte_timer/rte_timer.h
@@ -262,6 +262,12 @@ int rte_timer_reset(struct rte_timer *tim, uint64_t ticks,
  *   The callback function of the timer.
  * @param arg
  *   The user argument of the callback function.
+ *
+ * @note
+ *   This API should not be called inside a timer's callback function to
+ *   reset another timer; doing so could hang in certain scenarios. Instead,
+ *   the rte_timer_reset() API can be called directly and its return code
+ *   can be checked for success or failure.
  */
 void
 rte_timer_reset_sync(struct rte_timer *tim, uint64_t ticks,
@@ -301,6 +307,12 @@ int rte_timer_stop(struct rte_timer *tim);
  *
  * @param tim
  *   The timer handle.
+ *
+ * @note
+ *   This API should not be called inside a timer's callback function to
+ *   stop another timer; doing so could hang in certain scenarios. Instead, the
+ *   rte_timer_stop() API can be called directly and its return code can
+ *   be checked for success or failure.
  */
 void rte_timer_stop_sync(struct rte_timer *tim);