splice: fix misuse of SPLICE_F_NONBLOCK

commit 6965031d331a642e31278fa1b5bd47f372ffdd5d upstream.

SPLICE_F_NONBLOCK is clearly documented to only affect blocking on the
pipe.  In __generic_file_splice_read(), however, it causes an EAGAIN
if the page is currently being read.

This makes it impossible to write an application that only wants
failure if the pipe is full.  For example if the same process is
handling both ends of a pipe and isn't otherwise able to determine
whether a splice to the pipe will fill it or not.

We could make the read non-blocking on O_NONBLOCK or some other splice
flag, but for now this is the simplest fix.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/splice.c b/fs/splice.c
index eb602cbc1eb544c3f7a0ff954a8f4ab1073178f5..cc617b09e4c226175f610d2de56ece6e04777404 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -366,17 +366,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
                 * If the page isn't uptodate, we may need to start io on it
                 */
                if (!PageUptodate(page)) {
-                       /*
-                        * If in nonblock mode then dont block on waiting
-                        * for an in-flight io page
-                        */
-                       if (flags & SPLICE_F_NONBLOCK) {
-                               if (!trylock_page(page)) {
-                                       error = -EAGAIN;
-                                       break;
-                               }
-                       } else
-                               lock_page(page);
+                       lock_page(page);
 
                        /*
                         * Page was truncated, or invalidated by the