[PATCH 1/3] eventfd: Allow waiters to be notified about the eventfdfile* going away

From: Gregory Haskins
Date: Fri Jun 19 2009 - 14:52:04 EST

From: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>

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.

This is a feature, needed by KVM to avoid an awkward workaround when using

Signed-off-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Tested-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>

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

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 2a701d5..c71f51d 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -59,7 +59,15 @@ int eventfd_signal(struct file *file, int n)

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;

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/