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Date: Sat, 7 Dec 2002 20:55:50 +0000 (GMT)
From: Peter Benie <peterb@chiark.greenend.org.uk>
To: Alan.Cox@linux.org
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] [2.2] pipe_write can block even with non-blocking fd
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Please apply the following patch. This makes non-blocking writes to
pipe actually non-blocking.

A program that demonstrates the bug can be found at:
http://www.chiark.greenend.org.uk/~peterb/linux/nonblock/pipe-testnonblock.c

--- 2.2.19/fs/pipe.c.orig	Thu Dec  6 21:20:38 2001
+++ 2.2.19/fs/pipe.c	Thu Dec  6 21:22:47 2001
@@ -105,9 +105,17 @@
 	else
 		free = 1; /* can't do it atomically, wait for any free space */
 	up(&inode->i_sem);
-	if (down_interruptible(&inode->i_atomic_write)) {
-		down(&inode->i_sem);
-		return -ERESTARTSYS;
+	if (filp->f_flags & O_NONBLOCK) {
+		if (down_trylock(&inode->i_atomic_write)) {
+			down(&inode->i_sem);
+			return -ERESTARTSYS;
+		}
+	}
+	else {
+		if (down_interruptible(&inode->i_atomic_write)) {
+			down(&inode->i_sem);
+			return -ERESTARTSYS;
+		}
 	}
 	while (count>0) {
 		while ((PIPE_FREE(*inode) < free) || PIPE_LOCK(*inode)) {
-
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