From: Chuck Lever chuck.lever@oracle.com

commit f11ad7aa653130b71e2e89bed207f387718216d5 upstream.

RFC 8881 explains the purpose of the write verifier this way:

The final portion of the result is the field writeverf. This field is the write verifier and is a cookie that the client can use to determine whether a server has changed instance state (e.g., server restart) between a call to WRITE and a subsequent call to either WRITE or COMMIT.

But then it says:

This cookie MUST be unchanged during a single instance of the NFSv4.1 server and MUST be unique between instances of the NFSv4.1 server. If the cookie changes, then the client MUST assume that any data written with an UNSTABLE4 value for committed and an old writeverf in the reply has been lost and will need to be recovered.

RFC 1813 has similar language for NFSv3. NFSv2 does not have a write verifier since it doesn't implement the COMMIT procedure.

Since commit 19e0663ff9bc ("nfsd: Ensure sampling of the write verifier is atomic with the write"), the Linux NFS server has returned a boot-time-based verifier for UNSTABLE WRITEs, but a zero verifier for FILE_SYNC and DATA_SYNC WRITEs. FILE_SYNC and DATA_SYNC WRITEs are not followed up with a COMMIT, so there's no need for clients to compare verifiers for stable writes.

However, by returning a different verifier for stable and unstable writes, the above commit puts the Linux NFS server a step farther out of compliance with the first MUST above. At least one NFS client (FreeBSD) noticed the difference, making this a potential regression.

Reported-by: Rick Macklem rmacklem@uoguelph.ca Link: https://lore.kernel.org/linux-nfs/YQXPR0101MB096857EEACF04A6DF1FC6D9BDD749@Y... Fixes: 19e0663ff9bc ("nfsd: Ensure sampling of the write verifier is atomic with the write") Signed-off-by: Chuck Lever chuck.lever@oracle.com Signed-off-by: Michael Kochera kochera@google.com --- Removed down_write to fix the conflict in the cherry-pick. The down_write functionality was no longer needed there. Upstream commit 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb titled nfsd: Replace use of rwsem with errseq_t removed those and replace it with new functionality that was more scalable. This commit is already backported onto 5.10 and so removing down_write ensures consistency with that change. Tested by compiling and booting successfully.

fs/nfsd/vfs.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index c852bb5ff212..a4ae1fcd2ab1 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -1014,6 +1014,10 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf, iov_iter_kvec(&iter, WRITE, vec, vlen, *cnt); since = READ_ONCE(file->f_wb_err); if (flags & RWF_SYNC) { + if (verf) + nfsd_copy_boot_verifier(verf, + net_generic(SVC_NET(rqstp), + nfsd_net_id)); host_err = vfs_iter_write(file, &iter, &pos, flags); if (host_err < 0) nfsd_reset_boot_verifier(net_generic(SVC_NET(rqstp),