splice: only return -EAGAIN if there's hope of more data

sys_tee() currently is a bit eager in returning -EAGAIN, it may do so
even if we don't have a chance of anymore data becoming available. So
improve the logic and only return -EAGAIN if we have an attached writer
to the input pipe.

Reported by Johann Felix Soden <johfel@gmx.de> and
Patrick McManus <mcmanus@ducksong.com>.

Tested-by: Johann Felix Soden <johfel@users.sourceforge.net>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/splice.c b/fs/splice.c
index 9b559ee711a8..0670c915cd35 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1669,6 +1669,13 @@ static int link_pipe(struct pipe_inode_info *ipipe,
                 i++;
         } while (len);
 
+        /*
+         * return EAGAIN if we have the potential of some data in the
+         * future, otherwise just return 0
+         */
+        if (!ret && ipipe->waiting_writers && (flags & SPLICE_F_NONBLOCK))
+                ret = -EAGAIN;
+
         inode_double_unlock(ipipe->inode, opipe->inode);
 
         /*
@@ -1709,11 +1716,8 @@ static long do_tee(struct file *in, struct file *out, size_t len,
                 ret = link_ipipe_prep(ipipe, flags);
                 if (!ret) {
                         ret = link_opipe_prep(opipe, flags);
-                        if (!ret) {
+                        if (!ret)
                                 ret = link_pipe(ipipe, opipe, len, flags);
-                                if (!ret && (flags & SPLICE_F_NONBLOCK))
-                                        ret = -EAGAIN;
-                        }
                 }
         }