NFSD: Fix verifier returned in stable WRITEs
commit f11ad7aa 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 19e0663f ("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. [Removed down_write to fix the conflict in the cherry-pick. The down_write functionality was no longer needed there. Upstream commit 555dbf1a 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. - kochera] Reported-by:Rick Macklem <rmacklem@uoguelph.ca> Link: https://lore.kernel.org/linux-nfs/YQXPR0101MB096857EEACF04A6DF1FC6D9BDD749@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM/T/ Fixes: 19e0663f ("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> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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281e81a5
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