f2fs: do not preallocate blocks which has wrong buffer

Sheng Yong reports needless preallocation if write(small_buffer, large_size)
is called.

In that case, f2fs preallocates large_size, but vfs returns early due to
small_buffer size. Let's detect it before preallocation phase in f2fs.

Reported-by: Sheng Yong <shengyong1@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index e45522115b1c..9c0f469cde13 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -20,6 +20,7 @@
 #include <linux/uaccess.h>
 #include <linux/mount.h>
 #include <linux/pagevec.h>
+#include <linux/uio.h>
 #include <linux/uuid.h>
 #include <linux/file.h>
 
@@ -2258,8 +2259,12 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	inode_lock(inode);
 	ret = generic_write_checks(iocb, from);
 	if (ret > 0) {
-		int err = f2fs_preallocate_blocks(iocb, from);
+		int err;
 
+		if (iov_iter_fault_in_readable(from, iov_iter_count(from)))
+			set_inode_flag(inode, FI_NO_PREALLOC);
+
+		err = f2fs_preallocate_blocks(iocb, from);
 		if (err) {
 			inode_unlock(inode);
 			return err;
@@ -2267,6 +2272,7 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		blk_start_plug(&plug);
 		ret = __generic_file_write_iter(iocb, from);
 		blk_finish_plug(&plug);
+		clear_inode_flag(inode, FI_NO_PREALLOC);
 	}
 	inode_unlock(inode);