[PATCH v6 3/6] eal: avoid deadlock in async IPC alarm callback

[Anatoly Burakov]

async_reply_handle_thread_unsafe() can run while holding
pending_requests.lock and currently calls rte_eal_alarm_cancel().

rte_eal_alarm_cancel() may spin-wait for an executing callback, which can
deadlock if that callback is blocked on the same lock.

Remove callback-side alarm cancellation. It is safe to do so, because any
callback triggered without a pending request becomes a noop due to the
async request lookup now using numerical ID.

Fixes: daf9bfca717e ("ipc: remove thread for async requests")
Cc: stable at dpdk.org

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
---
 lib/eal/common/eal_common_proc.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/lib/eal/common/eal_common_proc.c b/lib/eal/common/eal_common_proc.c
index 3e32ee5027..869ce99bf9 100644
--- a/lib/eal/common/eal_common_proc.c
+++ b/lib/eal/common/eal_common_proc.c
@@ -549,19 +549,6 @@ async_reply_handle_thread_unsafe(struct pending_request *req)
 
 	TAILQ_REMOVE(&pending_requests.requests, req, next);
 
-	if (rte_eal_alarm_cancel(async_reply_handle,
-			(void *)(uintptr_t)req->id) < 0) {
-		/* if we failed to cancel the alarm because it's already in
-		 * progress, don't proceed because otherwise we will end up
-		 * handling the same message twice.
-		 */
-		if (rte_errno == EINPROGRESS) {
-			EAL_LOG(DEBUG, "Request handling is already in progress");
-			goto no_trigger;
-		}
-		EAL_LOG(ERR, "Failed to cancel alarm");
-	}
-
 	if (action == ACTION_TRIGGER)
 		return req;
 no_trigger:
-- 
2.47.3