linux-kernel - [patch] epoll - send POLLHUP on ->release

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Date:	Wed, 3 Jun 2009 12:00:22 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: [patch] epoll - send POLLHUP on ->release

The following patch allows waiters to be notified about the eventfd file* 
going away, and give them a change to unregister from the wait queue.
This is turn allows eventfd users to use the eventfd file* w/out 
holding a live reference to it.
After the eventfd user callbacks returns, any usage of the eventfd file* 
should be dropped. The eventfd user callback can acquire sleepy locks 
since it is invoked lockless.



Signed-off-by: Davide Libenzi <davidel@...ilserver.org>


- Davide


---
 fs/eventfd.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Index: linux-2.6.mod/fs/eventfd.c
===================================================================
--- linux-2.6.mod.orig/fs/eventfd.c	2009-05-27 12:10:03.000000000 -0700
+++ linux-2.6.mod/fs/eventfd.c	2009-05-27 12:16:57.000000000 -0700
@@ -59,7 +59,15 @@ int eventfd_signal(struct file *file, in
 
 static int eventfd_release(struct inode *inode, struct file *file)
 {
-	kfree(file->private_data);
+	struct eventfd_ctx *ctx = file->private_data;
+
+	/*
+	 * No need to hold the lock here, since we are on the file cleanup
+	 * path and the ones still attached to the wait queue will be
+	 * serialized by wake_up_locked_poll().
+	 */
+	wake_up_locked_poll(&ctx->wqh, POLLHUP);
+	kfree(ctx);
 	return 0;
 }
 
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