NTFS: 2.0.18 - Fix race condition in reading of compressed files.

- There was a narrow window between checking a buffer head for being
uptodate and locking it in ntfs_file_read_compressed_block(). We now
lock the buffer and then check whether it is uptodate or not.

Documentation/filesystems/ntfs.txt

@@ -247,6 +247,8 @@ ChangeLog
 
 Note, a technical ChangeLog aimed at kernel hackers is in fs/ntfs/ChangeLog.
 
+2.0.18:
+	- Fix race condition in reading of compressed files.
 2.0.17:
 	- Cleanups and optimizations.
 2.0.16:

fs/ntfs/ChangeLog

@@ -13,6 +13,14 @@ ToDo:
 	  with initialized_size < data_size. I don't think it can happen but
 	  it requires more careful consideration.
 	- Enable NFS exporting of NTFS.
+	- Apply block resolution optimization from aops.c::ntfs_read_block() to
+	  compress.c::ntfs_file_read_compressed_block() as well.
+
+2.0.18 - Fix race condition in reading of compressed files.
+
+	- There was a narrow window between checking a buffer head for being
+	  uptodate and locking it in ntfs_file_read_compressed_block(). We now
+	  lock the buffer and then check whether it is uptodate or not.
 
 2.0.17 - Cleanups and optimizations - shrinking the ToDo list.
 

fs/ntfs/Makefile

@@ -5,7 +5,7 @@ obj-$(CONFIG_NTFS_FS) += ntfs.o
 ntfs-objs := aops.o attrib.o compress.o debug.o dir.o file.o inode.o mft.o \
 	     mst.o namei.o super.o sysctl.o time.o unistr.o upcase.o
 
-EXTRA_CFLAGS = -DNTFS_VERSION=\"2.0.17\"
+EXTRA_CFLAGS = -DNTFS_VERSION=\"2.0.18\"
 
 ifeq ($(CONFIG_NTFS_DEBUG),y)
 EXTRA_CFLAGS += -DDEBUG

fs/ntfs/compress.c

@@ -157,7 +157,7 @@ static int ntfs_decompress(struct page *dest_pages[], int *dest_index,
 
 	/* Default error code. */
 	int err = -EOVERFLOW;
-	
+
 	ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
 do_next_sb:
 	ntfs_debug("Beginning sub-block at offset = 0x%x in the cb.",
@@ -193,7 +193,7 @@ static int ntfs_decompress(struct page *dest_pages[], int *dest_index,
 	/* Setup offsets for the current sub-block destination. */
 	do_sb_start = *dest_ofs;
 	do_sb_end = do_sb_start + NTFS_SB_SIZE;
-	
+
 	/* Check that we are still within allowed boundaries. */
 	if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
 		goto return_overflow;
@@ -572,11 +572,13 @@ int ntfs_file_read_compressed_block(struct page *page)
 	for (i = 0; i < nr_bhs; i++) {
 		struct buffer_head *tbh = bhs[i];
 
-		if (buffer_uptodate(tbh))
+		if (unlikely(test_set_buffer_locked(tbh)))
 			continue;
-
-		lock_buffer(tbh);
-		get_bh(tbh);
+		if (unlikely(buffer_uptodate(tbh))) {
+			unlock_buffer(tbh);
+			continue;
+		}
+		atomic_inc(&tbh->b_count);
 		tbh->b_end_io = end_buffer_io_sync;
 		submit_bh(READ, tbh);
 	}
@@ -587,9 +589,8 @@ int ntfs_file_read_compressed_block(struct page *page)
 
 		if (buffer_uptodate(tbh))
 			continue;
-
 		wait_on_buffer(tbh);
-		if (!buffer_uptodate(tbh))
+		if (unlikely(!buffer_uptodate(tbh)))
 			goto read_err;
 	}