Re: [PATCH] nfsd: decrease cl_cb_inflight if fail to queue cb_work

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2025-02-18 at 21:54 +0800, Li Lingfeng wrote:
> In nfsd4_run_cb, cl_cb_inflight is increased before attempting to queue
> cb_work to callback_wq. This count can be decreased in three situations:
> 1) If queuing fails in nfsd4_run_cb, the count will be decremented
> accordingly.
> 2) After cb_work is running, the count is decreased in the exception
> branch of nfsd4_run_cb_work via nfsd41_destroy_cb.
> 3) The count is decreased in the release callback of rpc_task — either
> directly calling nfsd41_cb_inflight_end in nfsd4_cb_probe_release, or
> calling nfsd41_destroy_cb in nfsd4_cb_release.
> 
> However, in nfsd4_cb_release, if the current cb_work needs to restart, the
> count will not be decreased, with the expectation that it will be reduced
> once cb_work is running.
> If queuing fails here, then the count will leak, ultimately causing the
> nfsd service to be unable to exit as shown below:
> [root@nfs_test2 ~]# cat /proc/2271/stack
> [<0>] nfsd4_shutdown_callback+0x22b/0x290
> [<0>] __destroy_client+0x3cd/0x5c0
> [<0>] nfs4_state_destroy_net+0xd2/0x330
> [<0>] nfs4_state_shutdown_net+0x2ad/0x410
> [<0>] nfsd_shutdown_net+0xb7/0x250
> [<0>] nfsd_last_thread+0x15f/0x2a0
> [<0>] nfsd_svc+0x388/0x3f0
> [<0>] write_threads+0x17e/0x2b0
> [<0>] nfsctl_transaction_write+0x91/0xf0
> [<0>] vfs_write+0x1c4/0x750
> [<0>] ksys_write+0xcb/0x170
> [<0>] do_syscall_64+0x70/0x120
> [<0>] entry_SYSCALL_64_after_hwframe+0x78/0xe2
> [root@nfs_test2 ~]#
> 
> Fix this by decreasing cl_cb_inflight if the restart fails.
> 
> Fixes: cba5f62b1830 ("nfsd: fix callback restarts")
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
> ---
>  fs/nfsd/nfs4callback.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> index 484077200c5d..8a7d24efdd08 100644
> --- a/fs/nfsd/nfs4callback.c
> +++ b/fs/nfsd/nfs4callback.c
> @@ -1459,12 +1459,16 @@ static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
>  static void nfsd4_cb_release(void *calldata)
>  {
>  	struct nfsd4_callback *cb = calldata;
> +	struct nfs4_client *clp = cb->cb_clp;
> +	int queued;
>  
>  	trace_nfsd_cb_rpc_release(cb->cb_clp);
>  
> -	if (cb->cb_need_restart)
> -		nfsd4_queue_cb(cb);
> -	else
> +	if (cb->cb_need_restart) {
> +		queued = nfsd4_queue_cb(cb);
> +		if (!queued)
> +			nfsd41_cb_inflight_end(clp);
> +	} else
>  		nfsd41_destroy_cb(cb);
>  
>  }

Good catch!

Reviewed-by: Jeff Layton <jlayton@kernel.org>