relayfs: fix infinite loop with splice()

Running kmemtraced, which uses splice() on relayfs, causes a hard lock on
x86-64 SMP.  As described by Tom Zanussi:

  It looks like you hit the same problem as described here:

  commit 8191ecd1d14c6914c660dfa007154860a7908857

      splice: fix infinite loop in generic_file_splice_read()

  relay uses the same loop but it never got noticed or fixed.

Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Tested-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/kernel/relay.c b/kernel/relay.c
index 32b0befdcb6a..09ac2008f77b 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1317,12 +1317,9 @@ static ssize_t relay_file_splice_read(struct file *in,
                 if (ret < 0)
                         break;
                 else if (!ret) {
-                        if (spliced)
-                                break;
-                        if (flags & SPLICE_F_NONBLOCK) {
+                        if (flags & SPLICE_F_NONBLOCK)
                                 ret = -EAGAIN;
-                                break;
-                        }
+                        break;
                 }
 
                 *ppos += ret;