debugfs: add API to allow debugfs operations cancellation

[linux-2.6-microblaze.git] / fs / debugfs / file.c

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 3eff924..5568cde 100644 (file)
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -114,6 +114,8 @@ int debugfs_file_get(struct dentry *dentry)
                lockdep_init_map(&fsd->lockdep_map, fsd->lock_name ?: "debugfs",
                                 &fsd->key, 0);
 #endif
+               INIT_LIST_HEAD(&fsd->cancellations);
+               mutex_init(&fsd->cancellations_mtx);
        }
 
        /*
@@ -156,6 +158,86 @@ void debugfs_file_put(struct dentry *dentry)
 }
 EXPORT_SYMBOL_GPL(debugfs_file_put);
 
+/**
+ * debugfs_enter_cancellation - enter a debugfs cancellation
+ * @file: the file being accessed
+ * @cancellation: the cancellation object, the cancel callback
+ *     inside of it must be initialized
+ *
+ * When a debugfs file is removed it needs to wait for all active
+ * operations to complete. However, the operation itself may need
+ * to wait for hardware or completion of some asynchronous process
+ * or similar. As such, it may need to be cancelled to avoid long
+ * waits or even deadlocks.
+ *
+ * This function can be used inside a debugfs handler that may
+ * need to be cancelled. As soon as this function is called, the
+ * cancellation's 'cancel' callback may be called, at which point
+ * the caller should proceed to call debugfs_leave_cancellation()
+ * and leave the debugfs handler function as soon as possible.
+ * Note that the 'cancel' callback is only ever called in the
+ * context of some kind of debugfs_remove().
+ *
+ * This function must be paired with debugfs_leave_cancellation().
+ */
+void debugfs_enter_cancellation(struct file *file,
+                               struct debugfs_cancellation *cancellation)
+{
+       struct debugfs_fsdata *fsd;
+       struct dentry *dentry = F_DENTRY(file);
+
+       INIT_LIST_HEAD(&cancellation->list);
+
+       if (WARN_ON(!d_is_reg(dentry)))
+               return;
+
+       if (WARN_ON(!cancellation->cancel))
+               return;
+
+       fsd = READ_ONCE(dentry->d_fsdata);
+       if (WARN_ON(!fsd ||
+                   ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
+               return;
+
+       mutex_lock(&fsd->cancellations_mtx);
+       list_add(&cancellation->list, &fsd->cancellations);
+       mutex_unlock(&fsd->cancellations_mtx);
+
+       /* if we're already removing wake it up to cancel */
+       if (d_unlinked(dentry))
+               complete(&fsd->active_users_drained);
+}
+EXPORT_SYMBOL_GPL(debugfs_enter_cancellation);
+
+/**
+ * debugfs_leave_cancellation - leave cancellation section
+ * @file: the file being accessed
+ * @cancellation: the cancellation previously registered with
+ *     debugfs_enter_cancellation()
+ *
+ * See the documentation of debugfs_enter_cancellation().
+ */
+void debugfs_leave_cancellation(struct file *file,
+                               struct debugfs_cancellation *cancellation)
+{
+       struct debugfs_fsdata *fsd;
+       struct dentry *dentry = F_DENTRY(file);
+
+       if (WARN_ON(!d_is_reg(dentry)))
+               return;
+
+       fsd = READ_ONCE(dentry->d_fsdata);
+       if (WARN_ON(!fsd ||
+                   ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
+               return;
+
+       mutex_lock(&fsd->cancellations_mtx);
+       if (!list_empty(&cancellation->list))
+               list_del(&cancellation->list);
+       mutex_unlock(&fsd->cancellations_mtx);
+}
+EXPORT_SYMBOL_GPL(debugfs_leave_cancellation);
+
 /*
  * Only permit access to world-readable files when the kernel is locked down.
  * We also need to exclude any file that has ways to write or alter it as root