[RFC PATCH 08/21] pipe: Check for ring full inside of the spinlock in pipe_write()

[David Howells]

Make pipe_write() check to see if the ring has become full between it
taking the pipe mutex, checking the ring status and then taking the
spinlock.

This can happen if a notification is written into the pipe as that happens
without the pipe mutex.

Signed-off-by: David Howells <dhowe...@redhat.com>
---

 fs/pipe.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/pipe.c b/fs/pipe.c
index 289a887f6b5b..0255a5ca5097 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -462,6 +462,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
                        spin_lock_irq(&pipe->wait.lock);
 
                        head = pipe->head;
+                       if (head - pipe->tail == buffers) {
+                               spin_unlock_irq(&pipe->wait.lock);
+                               continue;
+                       }
+
                        pipe_commit_write(pipe, head + 1);
 
                        /* Always wake up, even if the copy fails. Otherwise