net: ena: fix rare uncompleted admin command false alarm

The current flow to detect admin completion is:
while (command_not_completed) {
	if (timeout)
		error

	check_for_completion()
		sleep()
   }
So in case the sleep took more than the timeout
(in case the thread/workqueue was not scheduled due to higher priority
task or prolonged VMexit), the driver can detect a stall even if
the completion is present.

The fix changes the order of this function to first check for
completion and only after that check if the timeout expired.

Fixes: 1738cd3ed342 ("Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 10 deletions

diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
index 08d11cede9c9..e1c2fab6292f 100644
--- a/drivers/net/ethernet/amazon/ena/ena_com.c
+++ b/drivers/net/ethernet/amazon/ena/ena_com.c
@@ -508,15 +508,20 @@ static int ena_com_comp_status_to_errno(u8 comp_status)
 static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_ctx,
                                                      struct ena_com_admin_queue *admin_queue)
 {
-        unsigned long flags;
-        u32 start_time;
+        unsigned long flags, timeout;
         int ret;
 
-        start_time = ((u32)jiffies_to_usecs(jiffies));
+        timeout = jiffies + ADMIN_CMD_TIMEOUT_US;
+
+        while (1) {
+                spin_lock_irqsave(&admin_queue->q_lock, flags);
+                ena_com_handle_admin_completion(admin_queue);
+                spin_unlock_irqrestore(&admin_queue->q_lock, flags);
 
-        while (comp_ctx->status == ENA_CMD_SUBMITTED) {
-                if ((((u32)jiffies_to_usecs(jiffies)) - start_time) >
-                    ADMIN_CMD_TIMEOUT_US) {
+                if (comp_ctx->status != ENA_CMD_SUBMITTED)
+                        break;
+
+                if (time_is_before_jiffies(timeout)) {
                         pr_err("Wait for completion (polling) timeout\n");
                         /* ENA didn't have any completion */
                         spin_lock_irqsave(&admin_queue->q_lock, flags);
@@ -528,10 +533,6 @@ static int ena_com_wait_and_process_admin_cq_polling(struct ena_comp_ctx *comp_c
                         goto err;
                 }
 
-                spin_lock_irqsave(&admin_queue->q_lock, flags);
-                ena_com_handle_admin_completion(admin_queue);
-                spin_unlock_irqrestore(&admin_queue->q_lock, flags);
-
                 msleep(100);
         }