pnfs: change layout state seqlock to a spinlock

This prepares for future changes, where the layout state needs
to change atomically with several other variables.  In particular,
it will need to know if lo->segs is empty, as we test that instead
of manipulating the NFS_LAYOUT_STATEID_SET bit.  Moreover, the
layoutstateid is not really a read-mostly structure, as it is
written almost as often as it is read.

The behavior of pnfs_get_layout_stateid is also slightly changed, so that
it no longer changes the stateid.  Its name is changed to +pnfs_choose_layoutget_stateid.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index f3f9915..4e28242 100644 (file)
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -1798,7 +1798,7 @@ encode_layoutget(struct xdr_stream *xdr,
        p = xdr_encode_hyper(p, args->range.offset);
        p = xdr_encode_hyper(p, args->range.length);
        p = xdr_encode_hyper(p, args->minlength);
-       pnfs_get_layout_stateid(&stateid, NFS_I(args->inode)->layout,
+       pnfs_choose_layoutget_stateid(&stateid, NFS_I(args->inode)->layout,
                                args->ctx->state);
        p = xdr_encode_opaque_fixed(p, &stateid.data, NFS4_STATEID_SIZE);
        *p = cpu_to_be32(args->maxcount);

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index 6736f9e..08313f5 100644 (file)
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -258,9 +258,6 @@ pnfs_clear_lseg_list(struct pnfs_layout_hdr *lo, struct list_head *tmp_list)
        /* List does not take a reference, so no need for put here */
        list_del_init(&lo->plh_layouts);
        spin_unlock(&clp->cl_lock);
-       write_seqlock(&lo->plh_seqlock);
-       clear_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags);
-       write_sequnlock(&lo->plh_seqlock);
 
        dprintk("%s:Return\n", __func__);
 }
@@ -319,69 +316,40 @@ pnfs_destroy_all_layouts(struct nfs_client *clp)
        }
 }
 
-/* update lo->plh_stateid with new if is more recent
- *
- * lo->plh_stateid could be the open stateid, in which case we just use what given.
- */
+/* update lo->plh_stateid with new if is more recent */
 static void
 pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo,
                        const nfs4_stateid *new)
 {
-       nfs4_stateid *old = &lo->plh_stateid;
-       bool overwrite = false;
-
-       write_seqlock(&lo->plh_seqlock);
-       if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags) ||
-           memcmp(old->stateid.other, new->stateid.other, sizeof(new->stateid.other)))
-               overwrite = true;
-       else {
-               u32 oldseq, newseq;
-
-               oldseq = be32_to_cpu(old->stateid.seqid);
-               newseq = be32_to_cpu(new->stateid.seqid);
-               if ((int)(newseq - oldseq) > 0)
-                       overwrite = true;
-       }
-       if (overwrite)
-               memcpy(&old->stateid, &new->stateid, sizeof(new->stateid));
-       write_sequnlock(&lo->plh_seqlock);
-}
-
-static void
-pnfs_layout_from_open_stateid(struct pnfs_layout_hdr *lo,
-                             struct nfs4_state *state)
-{
-       int seq;
+       u32 oldseq, newseq;
 
-       dprintk("--> %s\n", __func__);
-       write_seqlock(&lo->plh_seqlock);
-       do {
-               seq = read_seqbegin(&state->seqlock);
-               memcpy(lo->plh_stateid.data, state->stateid.data,
-                      sizeof(state->stateid.data));
-       } while (read_seqretry(&state->seqlock, seq));
-       set_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags);
-       write_sequnlock(&lo->plh_seqlock);
-       dprintk("<-- %s\n", __func__);
+       oldseq = be32_to_cpu(lo->plh_stateid.stateid.seqid);
+       newseq = be32_to_cpu(new->stateid.seqid);
+       if ((int)(newseq - oldseq) > 0)
+               memcpy(&lo->plh_stateid, &new->stateid, sizeof(new->stateid));
 }
 
-void
-pnfs_get_layout_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
-                       struct nfs4_state *open_state)
+int
+pnfs_choose_layoutget_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
+                             struct nfs4_state *open_state)
 {
-       int seq;
+       int status = 0;
 
        dprintk("--> %s\n", __func__);
-       do {
-               seq = read_seqbegin(&lo->plh_seqlock);
-               if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->plh_flags)) {
-                       /* This will trigger retry of the read */
-                       pnfs_layout_from_open_stateid(lo, open_state);
-               } else
-                       memcpy(dst->data, lo->plh_stateid.data,
-                              sizeof(lo->plh_stateid.data));
-       } while (read_seqretry(&lo->plh_seqlock, seq));
+       spin_lock(&lo->plh_inode->i_lock);
+       if (list_empty(&lo->plh_segs)) {
+               int seq;
+
+               do {
+                       seq = read_seqbegin(&open_state->seqlock);
+                       memcpy(dst->data, open_state->stateid.data,
+                              sizeof(open_state->stateid.data));
+               } while (read_seqretry(&open_state->seqlock, seq));
+       } else
+               memcpy(dst->data, lo->plh_stateid.data, sizeof(lo->plh_stateid.data));
+       spin_unlock(&lo->plh_inode->i_lock);
        dprintk("<-- %s\n", __func__);
+       return status;
 }
 
 /*
@@ -496,7 +464,6 @@ alloc_init_layout_hdr(struct inode *ino)
        lo->plh_refcount = 1;
        INIT_LIST_HEAD(&lo->plh_layouts);
        INIT_LIST_HEAD(&lo->plh_segs);
-       seqlock_init(&lo->plh_seqlock);
        lo->plh_inode = ino;
        return lo;
 }

diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index c2f1086..1093720 100644 (file)
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -44,7 +44,6 @@ struct pnfs_layout_segment {
 enum {
        NFS_LAYOUT_RO_FAILED = 0,       /* get ro layout failed stop trying */
        NFS_LAYOUT_RW_FAILED,           /* get rw layout failed stop trying */
-       NFS_LAYOUT_STATEID_SET,         /* have a valid layout stateid */
 };
 
 /* Per-layout driver specific registration structure */
@@ -63,7 +62,6 @@ struct pnfs_layout_hdr {
        unsigned long           plh_refcount;
        struct list_head        plh_layouts;   /* other client layouts */
        struct list_head        plh_segs;      /* layout segments list */
-       seqlock_t               plh_seqlock;   /* Protects the stateid */
        nfs4_stateid            plh_stateid;
        unsigned long           plh_flags;
        struct inode            *plh_inode;
@@ -143,8 +141,9 @@ int pnfs_layout_process(struct nfs4_layoutget *lgp);
 void pnfs_destroy_layout(struct nfs_inode *);
 void pnfs_destroy_all_layouts(struct nfs_client *);
 void put_layout_hdr(struct inode *inode);
-void pnfs_get_layout_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
-                            struct nfs4_state *open_state);
+int pnfs_choose_layoutget_stateid(nfs4_stateid *dst,
+                                 struct pnfs_layout_hdr *lo,
+                                 struct nfs4_state *open_state);
 
 
 static inline int lo_fail_bit(u32 iomode)