[PATCH AUTOSEL 6.17-5.4] NFSv4: handle ERR_GRACE on delegation recalls

[Sasha Levin <sashal@kernel.org>]

From: Olga Kornievskaia <okorniev@redhat.com>

[ Upstream commit be390f95242785adbf37d7b8a5101dd2f2ba891b ]

RFC7530 states that clients should be prepared for the return of
NFS4ERR_GRACE errors for non-reclaim lock and I/O requests.

Signed-off-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES
**Key Points**
- The change at `fs/nfs/nfs4proc.c:7876-7880` extends the recall retry
  loop so that `-NFS4ERR_GRACE` is treated exactly like
  `-NFS4ERR_DELAY`, matching RFC 7530’s requirement that non-reclaim
  requests retry during the server’s grace period; without it we
  prematurely exit the loop.
- When the old code bailed out on `-NFS4ERR_GRACE`, control returned up
  the stack, causing `nfs_delegation_claim_locks()` to propagate
  `-EAGAIN` (`fs/nfs/delegation.c:176-178`), which in turn made
  `nfs_end_delegation_return()` fall into the client-recovery path or
  abort the delegation (`fs/nfs/delegation.c:584-596`), disrupting
  otherwise healthy delegations after a server restart.
- Other lock paths already retry on `-NFS4ERR_GRACE` (see
  `fs/nfs/nfs4proc.c:7594-7604`), so this patch simply aligns the
  delegation-recall path with existing, well-tested behaviour and
  prevents unnecessary recovery storms.
- The fix is tiny, localized to the NFS client delegation logic, and
  carries minimal regression risk while addressing a real-world failure
  mode observed during grace periods; it is an ideal candidate for
  stable backporting.

 fs/nfs/nfs4proc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 611e6283c194f..4de3e4bd724b7 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -7872,10 +7872,10 @@ int nfs4_lock_delegation_recall(struct file_lock *fl, struct nfs4_state *state,
 		return err;
 	do {
 		err = _nfs4_do_setlk(state, F_SETLK, fl, NFS_LOCK_NEW);
-		if (err != -NFS4ERR_DELAY)
+		if (err != -NFS4ERR_DELAY && err != -NFS4ERR_GRACE)
 			break;
 		ssleep(1);
-	} while (err == -NFS4ERR_DELAY);
+	} while (err == -NFS4ERR_DELAY || err == -NFSERR_GRACE);
 	return nfs4_handle_delegation_recall_error(server, state, stateid, fl, err);
 }
 
-- 
2.51.0