nfs: nfs_page should take a ref on the head req

nfs_pages that aren't the the head of a group must take a reference on the
head as long as ->wb_head is set to it. This stops the head from hitting
a refcount of 0 while there is still an active nfs_page for the page group.

This avoids kref warnings in the writeback code when the page group head
is found and referenced.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 7368b2130a41..05a63593a61f 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -239,15 +239,21 @@ nfs_page_group_init(struct nfs_page *req, struct nfs_page *prev)
         WARN_ON_ONCE(prev == req);
 
         if (!prev) {
+                /* a head request */
                 req->wb_head = req;
                 req->wb_this_page = req;
         } else {
+                /* a subrequest */
                 WARN_ON_ONCE(prev->wb_this_page != prev->wb_head);
                 WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &prev->wb_head->wb_flags));
                 req->wb_head = prev->wb_head;
                 req->wb_this_page = prev->wb_this_page;
                 prev->wb_this_page = req;
 
+                /* All subrequests take a ref on the head request until
+                 * nfs_page_group_destroy is called */
+                kref_get(&req->wb_head->wb_kref);
+
                 /* grab extra ref if head request has extra ref from
                  * the write/commit path to handle handoff between write
                  * and commit lists */
@@ -271,6 +277,10 @@ nfs_page_group_destroy(struct kref *kref)
         struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref);
         struct nfs_page *tmp, *next;
 
+        /* subrequests must release the ref on the head request */
+        if (req->wb_head != req)
+                nfs_release_request(req->wb_head);
+
         if (!nfs_page_group_sync_on_bit(req, PG_TEARDOWN))
                 return;