fs: simplify handling of zero sized reads in __blockdev_direct_IO

Reject zero sized reads as soon as we know our I/O length, and don't
borther with locks or allocations that might have to be cleaned up
otherwise.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index ac5f164170e3..98ce3ac0d94b 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1200,6 +1200,10 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
                 }
         }
 
+        /* watch out for a 0 len io from a tricksy fs */
+        if (rw == READ && end == offset)
+                return 0;
+
         dio = kmalloc(sizeof(*dio), GFP_KERNEL);
         retval = -ENOMEM;
         if (!dio)
@@ -1213,8 +1217,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
 
         dio->flags = flags;
         if (dio->flags & DIO_LOCKING) {
-                /* watch out for a 0 len io from a tricksy fs */
-                if (rw == READ && end > offset) {
+                if (rw == READ) {
                         struct address_space *mapping =
                                         iocb->ki_filp->f_mapping;