[PATCH 5.10.y] nfsd: don't offer flexfiles layouts when NFSv3 isn't being served

[Sasha Levin <sashal@kernel.org>]

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit 5d28b2c920d9d9d3c45b41769342ad785eb372a7 ]

The flexfiles layout driver hands out a deviceinfo that names this server
as an NFSv3 DS (flexfilelayout.c hardcodes da->version = 3). With v3
disabled, the client can't talk to the DS: it loops on v3 NULL calls that
the server answers with PROG_MISMATCH, and I/O hangs in D state.

Skip LAYOUT_FLEX_FILES in nfsd4_setup_layout_type() unless v3 is enabled.

Reported-by: Benji Wiebe <itsme@benjiwiebe.com>
Closes: https://lore.kernel.org/linux-nfs/c734eeb8-8486-4491-bb4d-b9656cbaffbe@app.fastmail.com/
Fixes: 9b9960a0ca47 ("nfsd: Add a super simple flex file server")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260904-pnfs-ff-v1-1-5f502cf25401@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
[ sashal: adapted the flexfiles condition to replace an #ifdef guard instead of extending an existing IS_ENABLED() check ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4layouts.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
index bcf16dd07d488..f55092c66f42b 100644
--- a/fs/nfsd/nfs4layouts.c
+++ b/fs/nfsd/nfs4layouts.c
@@ -125,6 +125,7 @@ nfsd4_set_deviceid(struct nfsd4_deviceid *id, const struct svc_fh *fhp,
 
 void nfsd4_setup_layout_type(struct svc_export *exp)
 {
+	struct nfsd_net *nn = net_generic(exp->cd->net, nfsd_net_id);
 #if defined(CONFIG_NFSD_BLOCKLAYOUT) || defined(CONFIG_NFSD_SCSILAYOUT)
 	struct super_block *sb = exp->ex_path.mnt->mnt_sb;
 #endif
@@ -132,9 +133,9 @@ void nfsd4_setup_layout_type(struct svc_export *exp)
 	if (!(exp->ex_flags & NFSEXP_PNFS))
 		return;
 
-#ifdef CONFIG_NFSD_FLEXFILELAYOUT
-	exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
-#endif
+	if (IS_ENABLED(CONFIG_NFSD_FLEXFILELAYOUT) &&
+	    nfsd_vers(nn, 3, NFSD_TEST))
+		exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
 #ifdef CONFIG_NFSD_BLOCKLAYOUT
 	if (sb->s_export_op->get_uuid &&
 	    sb->s_export_op->map_blocks &&
-- 
2.53.0