Issue:
Two threads:
- A, executing rte_eal_alarm_cancel,
- B, executing eal_alarm_callback.
Such case can cause starvation of thread B. Please see that there is a
small time window between lock and unlock in thread A, so thread B must
be switched to within a very small time window, so that it can obtain
the lock.
Solution to this problem is use sched_yield(), which puts current thread
(A) at the end of thread execution priority queue and allows thread B to
execute.
The issue can be observed e.g. on hot-pluggable device detach path.
On such path, rte_alarm can used to check if DPDK has completed
the detachment. Waiting for completion, rte_eal_alarm_cancel
is called, while another thread periodically calls eal_alarm_callback
causing the issue to occur.
Signed-off-by: Wojciech Panfil <wojciech.pan...@intel.com>
---
lib/eal/freebsd/eal_alarm.c | 5 +++++
lib/eal/linux/eal_alarm.c | 5 +++++
lib/eal/windows/eal_alarm.c | 4 ++++
3 files changed, 14 insertions(+)
diff --git a/lib/eal/freebsd/eal_alarm.c b/lib/eal/freebsd/eal_alarm.c
index 94cae5f4b6..8425b4f5a2 100644
--- a/lib/eal/freebsd/eal_alarm.c
+++ b/lib/eal/freebsd/eal_alarm.c
@@ -318,7 +318,12 @@ rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void
*cb_arg)
}
ap_prev = ap;
}
+
rte_spinlock_unlock(&alarm_list_lk);
+
+ /* Yield control to a second thread executing
eal_alarm_callback to avoid its starvation,
+ * as it is waiting for the lock we have just released. */
+ sched_yield();
} while (executing != 0);
if (count == 0 && err == 0)
diff --git a/lib/eal/linux/eal_alarm.c b/lib/eal/linux/eal_alarm.c
index eeb096213b..5326b1895f 100644
--- a/lib/eal/linux/eal_alarm.c
+++ b/lib/eal/linux/eal_alarm.c
@@ -248,7 +248,12 @@ rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void
*cb_arg)
}
ap_prev = ap;
}
+
rte_spinlock_unlock(&alarm_list_lk);
+
+ /* Yield control to a second thread executing
eal_alarm_callback to avoid its starvation,
+ * as it is waiting for the lock we have just released. */
+ sched_yield();
} while (executing != 0);
if (count == 0 && err == 0)
diff --git a/lib/eal/windows/eal_alarm.c b/lib/eal/windows/eal_alarm.c
index 052af4b21b..43e8d7881f 100644
--- a/lib/eal/windows/eal_alarm.c
+++ b/lib/eal/windows/eal_alarm.c
@@ -211,6 +211,10 @@ rte_eal_alarm_cancel(rte_eal_alarm_callback cb_fn, void
*cb_arg)
}
rte_spinlock_unlock(&alarm_lock);
+
+ /* Yield control to a second thread executing
eal_alarm_callback to avoid its starvation,
+ * as it is waiting for the lock we have just released. */
+ SwitchToThread();
} while (executing);
rte_eal_trace_alarm_cancel(cb_fn, cb_arg, removed);
--
2.46.0
