nfs: fix nonblocking calls to nfs_page_group_lock

nfs_page_group_lock was calling wait_on_bit_lock even when told not to
block. Fix by first trying test_and_set_bit, followed by wait_on_bit_lock
if and only if blocking is allowed.  Return -EAGAIN if nonblocking and the
test_and_set of the bit was already locked.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Reviewed-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 7efa615..89d5d43 100644 (file)
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -143,23 +143,28 @@ nfs_iocounter_wait(struct nfs_io_counter *c)
  *
  * this lock must be held if modifying the page group list
  *
- * returns result from wait_on_bit_lock: 0 on success, < 0 on error
+ * return 0 on success, < 0 on error: -EDELAY if nonblocking or the
+ * result from wait_on_bit_lock
+ *
+ * NOTE: calling with nonblock=false should always have set the
+ *       lock bit (see fs/buffer.c and other uses of wait_on_bit_lock
+ *       with TASK_UNINTERRUPTIBLE), so there is no need to check the result.
  */
 int
 nfs_page_group_lock(struct nfs_page *req, bool nonblock)
 {
        struct nfs_page *head = req->wb_head;
-       int ret;
 
        WARN_ON_ONCE(head != head->wb_head);
 
-       do {
-               ret = wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
-                       TASK_UNINTERRUPTIBLE);
-       } while (!nonblock && ret != 0);
+       if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
+               return 0;
 
-       WARN_ON_ONCE(ret > 0);
-       return ret;
+       if (!nonblock)
+               return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
+                               TASK_UNINTERRUPTIBLE);
+
+       return -EAGAIN;
 }
 
 /*