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net-sysfs: prevent uncleared queues from being re-added

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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@kernel.org>
Link: https://patch.msgid.link/20250204170314.146022-4-atenart@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Antoine Tenart 2025-02-04 18:03:12 +01:00 committed by Jakub Kicinski
parent b7ecc1de51
commit 7e54f85c60
1 changed files with 32 additions and 0 deletions
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32
net/core/net-sysfs.c
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@ -1210,6 +1210,22 @@ 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)) {
netdev_warn_once(dev, "Cannot re-add rx queues before their removal completed");
return -EAGAIN;
}
/* Kobject_put later will trigger rx_queue_release call which
* decreases dev refcount: Take that reference here
*/
@ -1898,6 +1914,22 @@ 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)) {
netdev_warn_once(dev, "Cannot re-add tx queues before their removal completed");
return -EAGAIN;
}
/* Kobject_put later will trigger netdev_queue_release call
* which decreases dev refcount: Take that reference here
*/