Re: [PATCH 3/3] NFSD: Fix server reboot hang problem when callback workqueue is stuck

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2023-12-15 at 11:15 -0800, Dai Ngo wrote:
> If the callback workqueue is stuck, nfsd4_deleg_getattr_conflict will
> also stuck waiting for the callback request to be executed. This causes
> the client to hang waiting for the reply of the GETATTR and also causes
> the reboot of the NFS server to hang due to the pending NFS request.
> 
> Fix by replacing wait_on_bit with wait_on_bit_timeout with 20 seconds
> time out.
> 
> Reported-by: Wolfgang Walter <linux-nfs@stwm.de>
> Fixes: 6c41d9a9bd02 ("NFSD: handle GETATTR conflict with write delegation")
> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> ---
>  fs/nfsd/nfs4state.c | 6 +++++-
>  fs/nfsd/state.h     | 2 ++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 175f3e9f5822..0cc7d4953807 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -2948,6 +2948,9 @@ void nfs4_cb_getattr(struct nfs4_cb_fattr *ncf)
>  	if (test_and_set_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags))
>  		return;
>  
> +	/* set to proper status when nfsd4_cb_getattr_done runs */
> +	ncf->ncf_cb_status = NFS4ERR_IO;
> +
>  	refcount_inc(&dp->dl_stid.sc_count);
>  	if (!nfsd4_run_cb(&ncf->ncf_getattr)) {
>  		refcount_dec(&dp->dl_stid.sc_count);
> @@ -8558,7 +8561,8 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct inode *inode,
>  			nfs4_cb_getattr(&dp->dl_cb_fattr);
>  			spin_unlock(&ctx->flc_lock);
>  
> -			wait_on_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY, TASK_INTERRUPTIBLE);
> +			wait_on_bit_timeout(&ncf->ncf_cb_flags, CB_GETATTR_BUSY,
> +				TASK_INTERRUPTIBLE, NFSD_CB_GETATTR_TIMEOUT);

The RPC won't necessarily have timed out at this point, and it looks
like ncf_cb_status won't have been set to anything (and is probably
still 0?).

Don't you need to check whether the wait timed out or was successful?
What happens now when this times out?


>  			if (ncf->ncf_cb_status) {
>  				status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
>  				if (status != nfserr_jukebox ||
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index f96eaa8e9413..94563a6813a6 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -135,6 +135,8 @@ struct nfs4_cb_fattr {
>  /* bits for ncf_cb_flags */
>  #define	CB_GETATTR_BUSY		0
>  
> +#define	NFSD_CB_GETATTR_TIMEOUT	msecs_to_jiffies(20000) /* 20 secs */
> +

Why 20s?

>  /*
>   * Represents a delegation stateid. The nfs4_client holds references to these
>   * and they are put when it is being destroyed or when the delegation is


-- 
Jeff Layton <jlayton@kernel.org>