Re: [PATCH net 4/5] afs: Fix further netns teardown to cancel the preallocation charger

[Simon Horman <horms@kernel.org>]

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---
afs: Fix further netns teardown to cancel the preallocation charger

This commit modifies the afs network namespace teardown process to wait for
the preallocation charger work item. It addresses a small window where the
work item could be requeued after being cancelled by flushing the workqueue
on which the charger runs.

Link: https://sashiko.dev/#/patchset/20260609140911.838677-1-dhowells%40redhat.com

> diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
> --- a/fs/afs/rxrpc.c
> +++ b/fs/afs/rxrpc.c
> @@ -130,6 +130,7 @@ void afs_close_socket(struct afs_net *net)
>  	cancel_work_sync(&net->charge_preallocation_work);
>  	kernel_listen(net->socket, 0);
>  	flush_workqueue(afs_async_calls);
> +	flush_workqueue(afs_wq);

[Severity: High]
Will flushing the system-wide global workqueue here cause cross-namespace
stalls during teardown?

It appears afs_wq is allocated once in afs_init() as a system-wide workqueue
shared by all AFS network namespaces:

fs/afs/main.c:afs_init() {
    ...
    afs_wq = alloc_workqueue("afs", WQ_PERCPU, 0);
    ...
}

Other namespaces use afs_wq for operations like cell management, which can
block for tens of seconds waiting for userspace DNS lookups via the
request_key mechanism.

Since afs_close_socket() runs in the context of the global cleanup_net
worker thread, does this stall the destruction of all network namespaces
system-wide until unrelated AFS work across the entire system finishes?

Would it be safer to explicitly call
cancel_work_sync(&net->charge_preallocation_work) a second time here instead
of flushing the shared queue?