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nfsd: reset write verifier on deferred writeback errors

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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@meta.com>
Fixes: 555dbf1a9a ("nfsd: Replace use of rwsem with errseq_t")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-6
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Jeff Layton 2026-05-22 12:44:19 -04:00 committed by Chuck Lever
parent 57aee7a35b
commit 2090b05803
1 changed files with 5 additions and 1 deletions
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6
fs/nfsd/vfs.c
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@ -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: