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Message-ID: <20231018154804.420823-4-atenart@kernel.org>
Date: Wed, 18 Oct 2023 17:47:45 +0200
From: Antoine Tenart <atenart@...nel.org>
To: davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
edumazet@...gle.com
Cc: Antoine Tenart <atenart@...nel.org>,
netdev@...r.kernel.org,
gregkh@...uxfoundation.org,
mhocko@...e.com,
stephen@...workplumber.org
Subject: [RFC PATCH net-next 3/4] net-sysfs: prevent uncleared queues from being re-added
With the (upcoming) removal of the rtnl_trylock/restart_syscall logic
and because of how Tx/Rx queues are implemented (and their
requirements), it might happen that a queue is re-added before having
the chance to be cleared. In such rare case, do not complete the queue
addition operation.
Signed-off-by: Antoine Tenart <atenart@...nel.org>
---
net/core/net-sysfs.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index a9f712ef9925..75fb92c44291 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1160,6 +1160,20 @@ static int rx_queue_add_kobject(struct net_device *dev, int index)
struct kobject *kobj = &queue->kobj;
int error = 0;
+ /* Rx queues are cleared in rx_queue_release to allow later
+ * re-registration. This is triggered when their kobj refcount is
+ * dropped.
+ *
+ * If a queue is removed while both a read (or write) operation and a
+ * the re-addition of the same queue are pending (waiting on rntl_lock)
+ * it might happen that the re-addition will execute before the read,
+ * making the initial removal to never happen (queue's kobj refcount
+ * won't drop enough because of the pending read). In such rare case,
+ * return to allow the removal operation to complete.
+ */
+ if (unlikely(kobj->state_initialized))
+ return -EAGAIN;
+
/* Kobject_put later will trigger rx_queue_release call which
* decreases dev refcount: Take that reference here
*/
@@ -1775,6 +1789,20 @@ static int netdev_queue_add_kobject(struct net_device *dev, int index)
struct kobject *kobj = &queue->kobj;
int error = 0;
+ /* Tx queues are cleared in netdev_queue_release to allow later
+ * re-registration. This is triggered when their kobj refcount is
+ * dropped.
+ *
+ * If a queue is removed while both a read (or write) operation and a
+ * the re-addition of the same queue are pending (waiting on rntl_lock)
+ * it might happen that the re-addition will execute before the read,
+ * making the initial removal to never happen (queue's kobj refcount
+ * won't drop enough because of the pending read). In such rare case,
+ * return to allow the removal operation to complete.
+ */
+ if (unlikely(kobj->state_initialized))
+ return -EAGAIN;
+
/* Kobject_put later will trigger netdev_queue_release call
* which decreases dev refcount: Take that reference here
*/
--
2.41.0
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