Patch "net: ena: fix rare uncompleted admin command false alarm" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

net: ena: fix rare uncompleted admin command false alarm

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-ena-fix-rare-uncompleted-admin-command-false-alarm.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Netanel Belgazal <[email protected]>
Date: Sun, 11 Jun 2017 15:42:43 +0300
Subject: net: ena: fix rare uncompleted admin command false alarm

From: Netanel Belgazal <[email protected]>

[ Upstream commit a77c1aafcc906f657d1a0890c1d898be9ee1d5c9 ]

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.

---
 drivers/net/ethernet/amazon/ena/ena_com.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

@@ -508,15 +508,20 @@ static int ena_com_comp_status_to_errno(
 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 (comp_ctx->status == ENA_CMD_SUBMITTED) {
-		if ((((u32)jiffies_to_usecs(jiffies)) - start_time) >
-		    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);
+
+		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_admi
 			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);
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net-ena-disable-admin-msix-while-working-in-polling-mode.patch queue-4.9/net-ena-fix-race-condition-between-submit-and-completion-admin-command.patch queue-4.9/net-ena-fix-rare-uncompleted-admin-command-false-alarm.patch queue-4.9/net-ena-add-missing-unmap-bars-on-device-removal.patch queue-4.9/net-ena-add-missing-return-when-ena_com_get_io_handlers-fails.patch