Re: [PATCH] nfsd: reset write verifier on deferred writeback errors

[Chuck Lever]

On Fri, May 22, 2026, at 12:44 PM, Jeff Layton wrote:
> nfsd_vfs_write() and nfsd_commit() both call filemap_check_wb_err() to
> detect deferred writeback errors, but neither rotates the server's write
> verifier (nn->writeverf) when this check fails. Every other
> durable-storage-failure path in these functions calls
> commit_reset_write_verifier() before returning an error.
>
> The missing rotation means clients holding UNSTABLE write data under the
> current verifier will COMMIT, receive the unchanged verifier back, and
> conclude their data is durable — silently dropping data that failed
> writeback. This violates the UNSTABLE+COMMIT durability contract
> (RFC 1813 §3.3.7, RFC 8881 §18.32).
>
> Add commit_reset_write_verifier() calls at both filemap_check_wb_err()
> error sites, matching the pattern used by adjacent error paths in the
> same functions. The helper already filters -EAGAIN and -ESTALE
> internally, so the calls are unconditionally safe.
>
> Reported-by: Chris Mason <clm@xxxxxxxx>
> Assisted-by: kres:claude-opus-4-6
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/nfsd/vfs.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index cba473969429..7e6468bdc723 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1513,8 +1513,10 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct 
> svc_fh *fhp,
>  	nfsd_stats_io_write_add(nn, exp, *cnt);
>  	fsnotify_modify(file);
>  	host_err = filemap_check_wb_err(file->f_mapping, since);
> -	if (host_err < 0)
> +	if (host_err < 0) {
> +		commit_reset_write_verifier(nn, rqstp, host_err);
>  		goto out_nfserr;
> +	}
> 
>  	if (stable && fhp->fh_use_wgather) {
>  		host_err = wait_for_concurrent_writes(file);
> @@ -1694,6 +1696,8 @@ nfsd_commit(struct svc_rqst *rqstp, struct svc_fh 
> *fhp, struct nfsd_file *nf,
>  			nfsd_copy_write_verifier(verf, nn);
>  			err2 = filemap_check_wb_err(nf->nf_file->f_mapping,
>  						    since);
> +			if (err2 < 0)
> +				commit_reset_write_verifier(nn, rqstp, err2);
>  			err = nfserrno(err2);
>  			break;
>  		case -EINVAL:
>
> ---
> base-commit: 6167e81847ba3adca17d8881ed9415beae993e2d
> change-id: 20260522-missing_verifier_reset_on_wb_err-480eb64a4ebe
>
> Best regards,
> -- 
> Jeff Layton <jlayton@xxxxxxxxxx>

Do you have an additional fix pending that addresses the same bug
in the async COPY path? If not, I can post one.


-- 
Chuck Lever