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Subject: [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock
 in pipe_write() [ver #2]
From:   David Howells <dhowells@redhat.com>
To:     torvalds@linux-foundation.org
Cc:     dhowells@redhat.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        nicolas.dichtel@6wind.com, raven@themaw.net,
        Christian Brauner <christian@brauner.io>, dhowells@redhat.com,
        keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-block@vger.kernel.org, linux-security-module@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 23 Oct 2019 21:18:36 +0100
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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 <dhowells@redhat.com>
---

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

diff --git a/fs/pipe.c b/fs/pipe.c
index 3df93990dd9d..6a982a88f658 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -462,6 +462,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 =09=09=09spin_lock_irq(&pipe->wait.lock);
=20
 =09=09=09head =3D pipe->head;
+=09=09=09if (pipe_full(head, pipe->tail, max_usage)) {
+=09=09=09=09spin_unlock_irq(&pipe->wait.lock);
+=09=09=09=09continue;
+=09=09=09}
+
 =09=09=09pipe_commit_write(pipe, head + 1);
=20
 =09=09=09/* Always wake up, even if the copy fails. Otherwise