1 files changed, 93 insertions, 6 deletions

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 5a84fd7109ad..1d8332563863 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -40,8 +40,10 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
 
         _debug("--- monitor %p %lx ---", page, page->flags);
 
-        if (!PageUptodate(page) && !PageError(page))
-                dump_stack();
+        if (!PageUptodate(page) && !PageError(page)) {
+                /* unlocked, not uptodate and not erronous? */
+                _debug("page probably truncated");
+        }
 
         /* remove from the waitqueue */
         list_del(&wait->task_list);
@@ -61,6 +63,84 @@ static int cachefiles_read_waiter(wait_queue_t *wait, unsigned mode,
 }
 
 /*
+ * handle a probably truncated page
+ * - check to see if the page is still relevant and reissue the read if
+ *   possible
+ * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
+ *   must wait again and 0 if successful
+ */
+static int cachefiles_read_reissue(struct cachefiles_object *object,
+                                   struct cachefiles_one_read *monitor)
+{
+        struct address_space *bmapping = object->backer->d_inode->i_mapping;
+        struct page *backpage = monitor->back_page, *backpage2;
+        int ret;
+
+        kenter("{ino=%lx},{%lx,%lx}",
+               object->backer->d_inode->i_ino,
+               backpage->index, backpage->flags);
+
+        /* skip if the page was truncated away completely */
+        if (backpage->mapping != bmapping) {
+                kleave(" = -ENODATA [mapping]");
+                return -ENODATA;
+        }
+
+        backpage2 = find_get_page(bmapping, backpage->index);
+        if (!backpage2) {
+                kleave(" = -ENODATA [gone]");
+                return -ENODATA;
+        }
+
+        if (backpage != backpage2) {
+                put_page(backpage2);
+                kleave(" = -ENODATA [different]");
+                return -ENODATA;
+        }
+
+        /* the page is still there and we already have a ref on it, so we don't
+         * need a second */
+        put_page(backpage2);
+
+        INIT_LIST_HEAD(&monitor->op_link);
+        add_page_wait_queue(backpage, &monitor->monitor);
+
+        if (trylock_page(backpage)) {
+                ret = -EIO;
+                if (PageError(backpage))
+                        goto unlock_discard;
+                ret = 0;
+                if (PageUptodate(backpage))
+                        goto unlock_discard;
+
+                kdebug("reissue read");
+                ret = bmapping->a_ops->readpage(NULL, backpage);
+                if (ret < 0)
+                        goto unlock_discard;
+        }
+
+        /* but the page may have been read before the monitor was installed, so
+         * the monitor may miss the event - so we have to ensure that we do get
+         * one in such a case */
+        if (trylock_page(backpage)) {
+                _debug("jumpstart %p {%lx}", backpage, backpage->flags);
+                unlock_page(backpage);
+        }
+
+        /* it'll reappear on the todo list */
+        kleave(" = -EINPROGRESS");
+        return -EINPROGRESS;
+
+unlock_discard:
+        unlock_page(backpage);
+        spin_lock_irq(&object->work_lock);
+        list_del(&monitor->op_link);
+        spin_unlock_irq(&object->work_lock);
+        kleave(" = %d", ret);
+        return ret;
+}
+
+/*
  * copy data from backing pages to netfs pages to complete a read operation
  * - driven by FS-Cache's thread pool
  */
@@ -92,20 +172,26 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
 
                 _debug("- copy {%lu}", monitor->back_page->index);
 
-                error = -EIO;
+        recheck:
                 if (PageUptodate(monitor->back_page)) {
                         copy_highpage(monitor->netfs_page, monitor->back_page);
 
                         pagevec_add(&pagevec, monitor->netfs_page);
                         fscache_mark_pages_cached(monitor->op, &pagevec);
                         error = 0;
-                }
-
-                if (error)
+                } else if (!PageError(monitor->back_page)) {
+                        /* the page has probably been truncated */
+                        error = cachefiles_read_reissue(object, monitor);
+                        if (error == -EINPROGRESS)
+                                goto next;
+                        goto recheck;
+                } else {
                         cachefiles_io_error_obj(
                                 object,
                                 "Readpage failed on backing file %lx",
                                 (unsigned long) monitor->back_page->flags);
+                        error = -EIO;
+                }
 
                 page_cache_release(monitor->back_page);
 
@@ -114,6 +200,7 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
                 fscache_put_retrieval(op);
                 kfree(monitor);
 
+        next:
                 /* let the thread pool have some air occasionally */
                 max--;
                 if (max < 0 || need_resched()) {