Subject: [PATCH net v2 1/3] net: ipa: fix atomic update in ipa_endpoint_replenish()

From: Alex Elder <[email-masked]>
Date: Wed, 12 Jan 2022 07:30:10 -0600

In ipa_endpoint_replenish(), if an error occurs when attempting to
replenish a receive buffer, we just quit and try again later.  In
that case we increment the backlog count to reflect that the attempt
was unsuccessful.  Then, if the add_one flag was true we increment
the backlog again.

This second increment is not included in the backlog local variable
though, and its value determines whether delayed work should be
scheduled.  This is a bug.

Fix this by determining whether 1 or 2 should be added to the
backlog before adding it in a atomic_add_return() call.

Reviewed-by: Matthias Kaehlcke <[email-masked]>
Fixes: 84f9bd12d46db ("soc: qcom: ipa: IPA endpoints")
Signed-off-by: Alex Elder <[email-masked]>
---
 drivers/net/ipa/ipa_endpoint.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ipa/ipa_endpoint.c b/drivers/net/ipa/ipa_endpoint.c
index 49d9a077d0375..8b055885cf3cf 100644
--- a/drivers/net/ipa/ipa_endpoint.c
+++ b/drivers/net/ipa/ipa_endpoint.c
@@ -1080,6 +1080,7 @@ static void ipa_endpoint_replenish(struct ipa_endpoint *endpoint, bool add_one)
 {
 	struct gsi *gsi;
 	u32 backlog;
+	int delta;
 
 	if (!endpoint->replenish_enabled) {
 		if (add_one)
@@ -1097,10 +1098,8 @@ static void ipa_endpoint_replenish(struct ipa_endpoint *endpoint, bool add_one)
 
 try_again_later:
 	/* The last one didn't succeed, so fix the backlog */
-	backlog = atomic_inc_return(&endpoint->replenish_backlog);
-
-	if (add_one)
-		atomic_inc(&endpoint->replenish_backlog);
+	delta = add_one ? 2 : 1;
+	backlog = atomic_add_return(delta, &endpoint->replenish_backlog);
 
 	/* Whenever a receive buffer transaction completes we'll try to
 	 * replenish again.  It's unlikely, but if we fail to supply even
-- 
2.32.0