pnfs: fix pnfs lock inversion of i_lock and cl_lock

The pnfs code was using throughout the lock order i_lock, cl_lock.
This conflicts with the nfs delegation code.  Rework the pnfs code
to avoid taking both locks simultaneously.

Currently the code takes the double lock to add/remove the layout to a
nfs_client list, while atomically checking that the list of lsegs is
empty.  To avoid this, we rely on existing serializations.  When a
layout is initialized with lseg count equal zero, LAYOUTGET's
openstateid serialization is in effect, making it safe to assume it
stays zero unless we change it.  And once a layout's lseg count drops
to zero, it is set as DESTROYED and so will stay at zero.

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

1 files changed, 25 insertions, 17 deletions

diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index c17edfbbaebf..0f5b66f90d17 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -247,13 +247,6 @@ put_lseg_locked(struct pnfs_layout_segment *lseg,
                 BUG_ON(test_bit(NFS_LSEG_VALID, &lseg->pls_flags));
                 list_del(&lseg->pls_list);
                 if (list_empty(&lseg->pls_layout->plh_segs)) {
-                        struct nfs_client *clp;
-
-                        clp = NFS_SERVER(ino)->nfs_client;
-                        spin_lock(&clp->cl_lock);
-                        /* List does not take a reference, so no need for put here */
-                        list_del_init(&lseg->pls_layout->plh_layouts);
-                        spin_unlock(&clp->cl_lock);
                         set_bit(NFS_LAYOUT_DESTROYED, &lseg->pls_layout->plh_flags);
                         /* Matched by initial refcount set in alloc_init_layout_hdr */
                         put_layout_hdr_locked(lseg->pls_layout);
@@ -319,11 +312,27 @@ mark_matching_lsegs_invalid(struct pnfs_layout_hdr *lo,
         return invalid - removed;
 }
 
+/* note free_me must contain lsegs from a single layout_hdr */
 void
 pnfs_free_lseg_list(struct list_head *free_me)
 {
         struct pnfs_layout_segment *lseg, *tmp;
+        struct pnfs_layout_hdr *lo;
+
+        if (list_empty(free_me))
+                return;
 
+        lo = list_first_entry(free_me, struct pnfs_layout_segment,
+                              pls_list)->pls_layout;
+
+        if (test_bit(NFS_LAYOUT_DESTROYED, &lo->plh_flags)) {
+                struct nfs_client *clp;
+
+                clp = NFS_SERVER(lo->plh_inode)->nfs_client;
+                spin_lock(&clp->cl_lock);
+                list_del_init(&lo->plh_layouts);
+                spin_unlock(&clp->cl_lock);
+        }
         list_for_each_entry_safe(lseg, tmp, free_me, pls_list) {
                 list_del(&lseg->pls_list);
                 free_lseg(lseg);
@@ -705,6 +714,7 @@ pnfs_update_layout(struct inode *ino,
         struct nfs_client *clp = NFS_SERVER(ino)->nfs_client;
         struct pnfs_layout_hdr *lo;
         struct pnfs_layout_segment *lseg = NULL;
+        bool first = false;
 
         if (!pnfs_enabled_sb(NFS_SERVER(ino)))
                 return NULL;
@@ -735,7 +745,10 @@ pnfs_update_layout(struct inode *ino,
         atomic_inc(&lo->plh_outstanding);
 
         get_layout_hdr(lo);
-        if (list_empty(&lo->plh_segs)) {
+        if (list_empty(&lo->plh_segs))
+                first = true;
+        spin_unlock(&ino->i_lock);
+        if (first) {
                 /* The lo must be on the clp list if there is any
                  * chance of a CB_LAYOUTRECALL(FILE) coming in.
                  */
@@ -744,17 +757,12 @@ pnfs_update_layout(struct inode *ino,
                 list_add_tail(&lo->plh_layouts, &clp->cl_layouts);
                 spin_unlock(&clp->cl_lock);
         }
-        spin_unlock(&ino->i_lock);
 
         lseg = send_layoutget(lo, ctx, iomode);
-        if (!lseg) {
-                spin_lock(&ino->i_lock);
-                if (list_empty(&lo->plh_segs)) {
-                        spin_lock(&clp->cl_lock);
-                        list_del_init(&lo->plh_layouts);
-                        spin_unlock(&clp->cl_lock);
-                }
-                spin_unlock(&ino->i_lock);
+        if (!lseg && first) {
+                spin_lock(&clp->cl_lock);
+                list_del_init(&lo->plh_layouts);
+                spin_unlock(&clp->cl_lock);
         }
         atomic_dec(&lo->plh_outstanding);
         put_layout_hdr(lo);