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>
diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
index c17edfb..0f5b66f 100644
--- a/fs/nfs/pnfs.c
+++ b/fs/nfs/pnfs.c
@@ -247,13 +247,6 @@
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 @@
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 @@
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 @@
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 @@
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);