[PATCH v2 12/21] nfsd: fix clock domain mismatch in clients_still_reclaiming()

[Jeff Layton <jlayton@kernel.org>]

clients_still_reclaiming() computes a deadline from nn->boot_time
(CLOCK_REALTIME, ~1.7 billion) but compares it against
ktime_get_boottime_seconds() (CLOCK_BOOTTIME, seconds since boot).
The comparison is always false — it would take ~54 years of uptime
for BOOTTIME to exceed the REALTIME-derived deadline.

This means any client can hold the server in grace indefinitely by
sending CLAIM_PREVIOUS OPEN requests, blocking all non-reclaim
operations for all other clients.

Add boot_time_bt (CLOCK_BOOTTIME) alongside the existing boot_time
and use it for the deadline computation. boot_time (CLOCK_REALTIME)
is preserved for its cl_boot clientid-nonce role.

Fixes: 20b7d86f29d3 ("nfsd: use boottime for lease expiry calculation")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/netns.h     | 1 +
 fs/nfsd/nfs4state.c | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 5c33c96da28e..03724bef10a7 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -78,6 +78,7 @@ struct nfsd_net {
 	struct lock_manager nfsd4_manager;
 	unsigned long flags;
 	time64_t boot_time;
+	time64_t boot_time_bt;	/* same instant in CLOCK_BOOTTIME */
 
 	struct dentry *nfsd_client_dir;
 
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 3dc0c0f6eb5d..17cb3b0ad956 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6870,7 +6870,7 @@ bool nfsd4_force_end_grace(struct nfsd_net *nn)
  */
 static bool clients_still_reclaiming(struct nfsd_net *nn)
 {
-	time64_t double_grace_period_end = nn->boot_time +
+	time64_t double_grace_period_end = nn->boot_time_bt +
 					   2 * nn->nfsd4_lease;
 
 	if (test_bit(NFSD_NET_GRACE_END_FORCED, &nn->flags))
@@ -9245,6 +9245,7 @@ static int nfs4_state_create_net(struct net *net)
 	nn->conf_name_tree = RB_ROOT;
 	nn->unconf_name_tree = RB_ROOT;
 	nn->boot_time = ktime_get_real_seconds();
+	nn->boot_time_bt = ktime_get_boottime_seconds();
 	clear_bit(NFSD_NET_GRACE_ENDED, &nn->flags);
 	clear_bit(NFSD_NET_GRACE_END_FORCED, &nn->flags);
 	nn->nfsd4_manager.block_opens = true;

-- 
2.54.0