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From: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
To: erik.g.carrillo@intel.com
Cc: stable@dpdk.org
Subject: [dpdk-stable] [PATCH 1/1] timer: add limitation note for sync stop and reset
Date: Wed,  9 Sep 2020 09:38:50 -0500
Message-ID: <1599662330-44663-2-git-send-email-erik.g.carrillo@intel.com> (raw)
In-Reply-To: <1599662330-44663-1-git-send-email-erik.g.carrillo@intel.com>

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>
---
 lib/librte_timer/rte_timer.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/librte_timer/rte_timer.h b/lib/librte_timer/rte_timer.h
index c6b3d45..d7c3e03 100644
--- a/lib/librte_timer/rte_timer.h
+++ b/lib/librte_timer/rte_timer.h
@@ -274,6 +274,12 @@ 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,
@@ -313,6 +319,12 @@ 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);
 
-- 
2.6.4


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Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1599662330-44663-1-git-send-email-erik.g.carrillo@intel.com>
2020-09-09 14:38 ` Erik Gabriel Carrillo [this message]
     [not found] <1599662474-44882-1-git-send-email-erik.g.carrillo@intel.com>
2020-09-09 14:41 ` Erik Gabriel Carrillo

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