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>

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 7368b21..05a6359 100644 (file)
--- 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;