NFS: Prevent a deadlock in the new writeback code
We have to unlock the nfs_page before we call nfs_end_page_writeback
to avoid races with functions that expect the page to be unlocked
when PG_locked and PG_writeback are not set.
The problem is that nfs_unlock_request also releases the nfs_page,
causing a deadlock if the release of the nfs_open_context
triggers an iput() while the PG_writeback flag is still set...
The solution is to separate the unlocking and release of the nfs_page,
so that we can do the former before nfs_end_page_writeback and the
latter after.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Fred Isaman <iisaman@netapp.com>
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 33a21ca..69146f3 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -128,10 +128,10 @@
}
/**
- * nfs_unlock_request - Unlock request and wake up sleepers.
+ * nfs_unlock_request_dont_release - Unlock request and wake up sleepers.
* @req:
*/
-void nfs_unlock_request(struct nfs_page *req)
+void nfs_unlock_request_dont_release(struct nfs_page *req)
{
if (!NFS_WBACK_BUSY(req)) {
printk(KERN_ERR "NFS: Invalid unlock attempted\n");
@@ -141,6 +141,14 @@
clear_bit(PG_BUSY, &req->wb_flags);
smp_mb__after_clear_bit();
wake_up_bit(&req->wb_flags, PG_BUSY);
+}
+
+/**
+ * nfs_unlock_request - Unlock request and release the nfs_page
+ */
+void nfs_unlock_request(struct nfs_page *req)
+{
+ nfs_unlock_request_dont_release(req);
nfs_release_request(req);
}