NFS: Fix races nfs_page_group_destroy() vs nfs_destroy_unlinked_subrequests()

When a subrequest is being detached from the subgroup, we want to
ensure that it is not holding the group lock, or in the process
of waiting for the group lock.

Fixes: 5b2b5187fa85 ("NFS: Fix nfs_page_group_destroy() and nfs_lock_and_join_requests() race cases")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

1 files changed, 45 insertions, 22 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index be5e209399ea..0e3f0f241d83 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -133,47 +133,70 @@ nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
 EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);
 
 /*
- * nfs_page_group_lock - lock the head of the page group
- * @req - request in group that is to be locked
+ * nfs_page_set_headlock - set the request PG_HEADLOCK
+ * @req: request that is to be locked
  *
- * this lock must be held when traversing or modifying the page
- * group list
+ * this lock must be held when modifying req->wb_head
  *
  * return 0 on success, < 0 on error
  */
 int
-nfs_page_group_lock(struct nfs_page *req)
+nfs_page_set_headlock(struct nfs_page *req)
 {
-	struct nfs_page *head = req->wb_head;
-
-	WARN_ON_ONCE(head != head->wb_head);
-
-	if (!test_and_set_bit(PG_HEADLOCK, &head->wb_flags))
+	if (!test_and_set_bit(PG_HEADLOCK, &req->wb_flags))
 		return 0;
 
-	set_bit(PG_CONTENDED1, &head->wb_flags);
+	set_bit(PG_CONTENDED1, &req->wb_flags);
 	smp_mb__after_atomic();
-	return wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK,
+	return wait_on_bit_lock(&req->wb_flags, PG_HEADLOCK,
 				TASK_UNINTERRUPTIBLE);
 }
 
 /*
- * nfs_page_group_unlock - unlock the head of the page group
- * @req - request in group that is to be unlocked
+ * nfs_page_clear_headlock - clear the request PG_HEADLOCK
+ * @req: request that is to be locked
  */
 void
-nfs_page_group_unlock(struct nfs_page *req)
+nfs_page_clear_headlock(struct nfs_page *req)
 {
-	struct nfs_page *head = req->wb_head;
-
-	WARN_ON_ONCE(head != head->wb_head);
-
 	smp_mb__before_atomic();
-	clear_bit(PG_HEADLOCK, &head->wb_flags);
+	clear_bit(PG_HEADLOCK, &req->wb_flags);
 	smp_mb__after_atomic();
-	if (!test_bit(PG_CONTENDED1, &head->wb_flags))
+	if (!test_bit(PG_CONTENDED1, &req->wb_flags))
 		return;
-	wake_up_bit(&head->wb_flags, PG_HEADLOCK);
+	wake_up_bit(&req->wb_flags, PG_HEADLOCK);
+}
+
+/*
+ * nfs_page_group_lock - lock the head of the page group
+ * @req: request in group that is to be locked
+ *
+ * this lock must be held when traversing or modifying the page
+ * group list
+ *
+ * return 0 on success, < 0 on error
+ */
+int
+nfs_page_group_lock(struct nfs_page *req)
+{
+	int ret;
+
+	ret = nfs_page_set_headlock(req);
+	if (ret || req->wb_head == req)
+		return ret;
+	return nfs_page_set_headlock(req->wb_head);
+}
+
+/*
+ * nfs_page_group_unlock - unlock the head of the page group
+ * @req: request in group that is to be unlocked
+ */
+void
+nfs_page_group_unlock(struct nfs_page *req)
+{
+	if (req != req->wb_head)
+		nfs_page_clear_headlock(req->wb_head);
+	nfs_page_clear_headlock(req);
 }
 
 /*