[PATCH v4 21/24] NFSv4: Use sequence counter with associated spinlock

[Ahmed S. Darwish]

A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darw...@linutronix.de>
---
 fs/nfs/nfs4_fs.h   | 2 +-
 fs/nfs/nfs4state.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index 2b7f6dcd2eb8..210e590e1f71 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -117,7 +117,7 @@ struct nfs4_state_owner {
        unsigned long        so_flags;
        struct list_head     so_states;
        struct nfs_seqid_counter so_seqid;
-       seqcount_t           so_reclaim_seqcount;
+       seqcount_spinlock_t  so_reclaim_seqcount;
        struct mutex         so_delegreturn_mutex;
 };
 
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index a8dc25ce48bb..b1dba24918f8 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -509,7 +509,7 @@ nfs4_alloc_state_owner(struct nfs_server *server,
        nfs4_init_seqid_counter(&sp->so_seqid);
        atomic_set(&sp->so_count, 1);
        INIT_LIST_HEAD(&sp->so_lru);
-       seqcount_init(&sp->so_reclaim_seqcount);
+       seqcount_spinlock_init(&sp->so_reclaim_seqcount, &sp->so_lock);
        mutex_init(&sp->so_delegreturn_mutex);
        return sp;
 }
-- 
2.20.1