mm: debug fing_get_pages speculative restart

From: Konstantin Khlebnikov <khlebnikov@openvz.org>

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 mm/filemap.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index a4a5260..a8cffef 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -815,6 +815,7 @@ unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
 	struct radix_tree_iter iter;
 	void **slot;
 	unsigned ret = 0;
+	int nr_found = 0;
 
 	if (unlikely(!nr_pages))
 		return 0;
@@ -846,6 +847,7 @@ repeat:
 			continue;
 		}
 
+		nr_found++;
 		if (!page_cache_get_speculative(page))
 			goto repeat;
 
@@ -861,6 +863,7 @@ repeat:
 	}
 
 	rcu_read_unlock();
+	WARN_ON(!ret && nr_found);
 	return ret;
 }
 
@@ -882,6 +885,7 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
 	struct radix_tree_iter iter;
 	void **slot;
 	unsigned int ret = 0;
+	int nr_found = 0;
 
 	if (unlikely(!nr_pages))
 		return 0;
@@ -913,6 +917,7 @@ repeat:
 			break;
 		}
 
+		nr_found++;
 		if (!page_cache_get_speculative(page))
 			goto repeat;
 
@@ -937,6 +942,7 @@ repeat:
 			break;
 	}
 	rcu_read_unlock();
+	WARN_ON(!ret && nr_found);
 	return ret;
 }
 EXPORT_SYMBOL(find_get_pages_contig);
@@ -958,6 +964,7 @@ unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 	struct radix_tree_iter iter;
 	void **slot;
 	unsigned ret = 0;
+	int nr_found = 0;
 
 	if (unlikely(!nr_pages))
 		return 0;
@@ -988,6 +995,7 @@ repeat:
 			BUG();
 		}
 
+		nr_found++;
 		if (!page_cache_get_speculative(page))
 			goto repeat;
 
@@ -1007,6 +1015,7 @@ repeat:
 	if (ret)
 		*index = pages[ret - 1]->index + 1;
 
+	WARN_ON(!ret && nr_found);
 	return ret;
 }
 EXPORT_SYMBOL(find_get_pages_tag);