not empty pages list after fuse_readpages

PATCH In review Alexander Zarochentsev 2 participants 3 messages Aug 9, 2006 – Aug 10, 2006

Subsystems (3)

Memory management Page cache FUSE filesystem core

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Alexander Zarochentsev

author

2006-08-09 20:20 UTC #0 lore raw

PATCH 1/1 not empty pages list after fuse_readpages

Hello,

fuse_readpages looks buggy for me because it doesn't care about making the @pages list empty at exit.

If it is indeed a bug, I suggest the following patch:

don't let fuse_readpages leave the @pages list not empty when exiting on error.

Signed-off-by Alexander Zarochentsev <[email protected]>

---
 fs/fuse/file.c          |   15 +++++++++++----
 include/linux/pagemap.h |    1 +
 mm/readahead.c          |   24 +++++++++++++++++-------
 3 files changed, 29 insertions(+), 11 deletions(-)

fs/fuse/file.c +12 -4

@@ -395,14 +395,18 @@ static int fuse_readpages(struct file *f
 	struct fuse_readpages_data data;
 	int err;
 
-	if (is_bad_inode(inode))
-		return -EIO;
+	if (is_bad_inode(inode)) {
+		err = -EIO;
+		goto clean_pages_up;
+	}
 
 	data.file = file;
 	data.inode = inode;
 	data.req = fuse_get_req(fc);
-	if (IS_ERR(data.req))
-		return PTR_ERR(data.req);
+	if (IS_ERR(data.req)) {
+		err = PTR_ERR(data.req);
+		goto clean_pages_up;
+	}
 
 	err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
 	if (!err) {

@@ -411,6 +415,10 @@ static int fuse_readpages(struct file *f
 		else
 			fuse_put_request(fc, data.req);
 	}
+	if (0) {
+clean_pages_up:
+		readpages_cleanup_helper(pages);
+	}
 	return err;
 }

include/linux/pagemap.h +1 -0

@@ -100,6 +100,7 @@ extern struct page * read_cache_page(str
 				void *data);
 extern int read_cache_pages(struct address_space *mapping,
 		struct list_head *pages, filler_t *filler, void *data);
+extern void readpages_cleanup_helper(struct list_head *);
 
 static inline struct page *read_mapping_page(struct address_space *mapping,
 					     unsigned long index, void *data)

mm/readahead.c +17 -7

@@ -229,6 +229,22 @@ static inline unsigned long get_next_ra_
 #define list_to_page(head) (list_entry((head)->prev, struct page, lru))
 
 /**
+ * may be useful in foo_fs_readpages method for the page pool cleanup
+ * before exiting on error.
+ */
+void readpages_cleanup_helper(struct list_head *pages)
+{
+	while (!list_empty(pages)) {
+		struct page *victim;
+
+		victim = list_to_page(pages);
+		list_del(&victim->lru);
+		page_cache_release(victim);
+	}
+}
+EXPORT_SYMBOL(readpages_cleanup_helper);
+
+/**
  * read_cache_pages - populate an address space with some pages & start reads against them
  * @mapping: the address_space
  * @pages: The address of a list_head which contains the target pages.  These

@@ -260,13 +276,7 @@ int read_cache_pages(struct address_spac
 			__pagevec_lru_add(&lru_pvec);
 		}
 		if (ret) {
-			while (!list_empty(pages)) {
-				struct page *victim;
-
-				victim = list_to_page(pages);
-				list_del(&victim->lru);
-				page_cache_release(victim);
-			}
+			readpages_cleanup_helper(pages);
 			break;
 		}
 	}

Alexander Zarochentsev

author

2006-08-10 03:54 UTC #2 lore raw

Quoted 10 lines · Dave Hansen

Review
Quoted 7 lines · Alexander Zarochentsev
        }
(quoted diff) +4 -0
+       if (0) {
+clean_pages_up:
+               readpages_cleanup_helper(pages);
+       }
        return err;
 }
If the list is really empty during a normal exit,

normal exit is done after read_cache_pages()
which always cleans the list. If read_cache_pages is not called, the list is not empty and
__do_page_cache_readahead: BUG_ON(!list_empty(&page_pool)) will be triggered.

Quoted 3 lines

does it hurt to
call the helper? The whole goto inside of an if(0) statement looks a little funky.

yes, a bit.

but really anybody has problems understanding it?

Quoted 8 lines

The following would be the same number of lines of code, and this is used pretty commonly in the kernel:
	return err;
clean_pages_up:
	readpages_cleanup_helper(pages);
	return err;

Quoted 5 lines

But, I really wonder what is wrong with this:
clean_pages_up:
	readpages_cleanup_helper(pages);
	return err;

unneeded function call?

well, the same patch without if(0):

don't let fuse_readpages leave the @pages list not empty when exiting on error.

Signed-off-by Alexander Zarochentsev <[email protected]>

---
 fs/fuse/file.c          |   15 +++++++++++----
 include/linux/pagemap.h |    1 +
 mm/readahead.c          |   24 +++++++++++++++++-------
 3 files changed, 29 insertions(+), 11 deletions(-)

fs/fuse/file.c +11 -4

@@ -395,14 +395,18 @@ static int fuse_readpages(struct file *f
 	struct fuse_readpages_data data;
 	int err;
 
-	if (is_bad_inode(inode))
-		return -EIO;
+	if (is_bad_inode(inode)) {
+		err = -EIO;
+		goto clean_pages_up;
+	}
 
 	data.file = file;
 	data.inode = inode;
 	data.req = fuse_get_req(fc);
-	if (IS_ERR(data.req))
-		return PTR_ERR(data.req);
+	if (IS_ERR(data.req)) {
+		err = PTR_ERR(data.req);
+		goto clean_pages_up;
+	}
 
 	err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
 	if (!err) {

@@ -412,6 +416,9 @@ static int fuse_readpages(struct file *f
 			fuse_put_request(fc, data.req);
 	}
 	return err;
+clean_pages_up:
+	readpages_cleanup_helper(pages);
+	return err;
 }
 
 static size_t fuse_send_write(struct fuse_req *req, struct file *file,

include/linux/pagemap.h +1 -0

@@ -100,6 +100,7 @@ extern struct page * read_cache_page(str
 				void *data);
 extern int read_cache_pages(struct address_space *mapping,
 		struct list_head *pages, filler_t *filler, void *data);
+extern void readpages_cleanup_helper(struct list_head *);
 
 static inline struct page *read_mapping_page(struct address_space *mapping,
 					     unsigned long index, void *data)

mm/readahead.c +17 -7

@@ -229,6 +229,22 @@ static inline unsigned long get_next_ra_
 #define list_to_page(head) (list_entry((head)->prev, struct page, lru))
 
 /**
+ * may be useful in foo_fs_readpages method for the page pool cleanup
+ * before exiting on error.
+ */
+void readpages_cleanup_helper(struct list_head *pages)
+{
+	while (!list_empty(pages)) {
+		struct page *victim;
+
+		victim = list_to_page(pages);
+		list_del(&victim->lru);
+		page_cache_release(victim);
+	}
+}
+EXPORT_SYMBOL(readpages_cleanup_helper);
+
+/**
  * read_cache_pages - populate an address space with some pages & start reads against them
  * @mapping: the address_space
  * @pages: The address of a list_head which contains the target pages.  These

@@ -260,13 +276,7 @@ int read_cache_pages(struct address_spac
 			__pagevec_lru_add(&lru_pvec);
 		}
 		if (ret) {
-			while (!list_empty(pages)) {
-				struct page *victim;
-
-				victim = list_to_page(pages);
-				list_del(&victim->lru);
-				page_cache_release(victim);
-			}
+			readpages_cleanup_helper(pages);
 			break;
 		}
 	}