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Date: Sun, 21 Jun 2009 09:51:24 -0700 (PDT)
From: Davide Libenzi <davidel@...ilserver.org>
To: Gregory Haskins <ghaskins@...ell.com>
cc: mst@...hat.com, kvm@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
avi@...hat.com, paulmck@...ux.vnet.ibm.com,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix
notifier race conditions
On Sat, 20 Jun 2009, Gregory Haskins wrote:
> Davide Libenzi wrote:
> > On Sat, 20 Jun 2009, Davide Libenzi wrote:
> >
> >
> >> On Sat, 20 Jun 2009, Davide Libenzi wrote:
> >>
> >>
> >>> How about the one below?
> >>>
> >> Maybe with an interface that can be undone w/out a file* :)
> >>
> >
> > This is another alternative, based on a low-carb diet of your notifier
> > patch.
> >
> Ah, I should always check if I have more mail before responding to a now
> stale patch ;)
Here. I changed the eventfd_pollcb_register() prototype to return the full
registeration time event mask, instead of the POLLIN explicit check.
Let's give this one some more thought before I push it to Andrew.
- Davide
---
fs/eventfd.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++-
include/linux/eventfd.h | 24 ++++++++++++
2 files changed, 117 insertions(+), 1 deletion(-)
Index: linux-2.6.mod/fs/eventfd.c
===================================================================
--- linux-2.6.mod.orig/fs/eventfd.c 2009-06-20 16:25:45.000000000 -0700
+++ linux-2.6.mod/fs/eventfd.c 2009-06-21 09:36:46.000000000 -0700
@@ -17,8 +17,10 @@
#include <linux/eventfd.h>
#include <linux/syscalls.h>
#include <linux/module.h>
+#include <linux/kref.h>
struct eventfd_ctx {
+ struct kref kref;
wait_queue_head_t wqh;
/*
* Every time that a write(2) is performed on an eventfd, the
@@ -59,9 +61,30 @@ int eventfd_signal(struct file *file, in
}
EXPORT_SYMBOL_GPL(eventfd_signal);
+static void eventfd_free(struct kref *kref)
+{
+ struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
+
+ kfree(ctx);
+}
+
+static struct eventfd_ctx *eventfd_get(struct eventfd_ctx *ctx)
+{
+ kref_get(&ctx->kref);
+ return ctx;
+}
+
+static void eventfd_put(struct eventfd_ctx *ctx)
+{
+ kref_put(&ctx->kref, eventfd_free);
+}
+
static int eventfd_release(struct inode *inode, struct file *file)
{
- kfree(file->private_data);
+ struct eventfd_ctx *ctx = file->private_data;
+
+ wake_up_poll(&ctx->wqh, POLLHUP);
+ eventfd_put(ctx);
return 0;
}
@@ -185,6 +208,14 @@ static const struct file_operations even
.write = eventfd_write,
};
+/**
+ * eventfd_fget - Acquire a reference of an eventfd file descriptor.
+ *
+ * @fd: [in] Eventfd file descriptor.
+ *
+ * Returns: A pointer to the eventfd file structure in case of success, or a
+ * proper error pointer in case of failure.
+ */
struct file *eventfd_fget(int fd)
{
struct file *file;
@@ -217,6 +248,7 @@ SYSCALL_DEFINE2(eventfd2, unsigned int,
if (!ctx)
return -ENOMEM;
+ kref_init(&ctx->kref);
init_waitqueue_head(&ctx->wqh);
ctx->count = count;
ctx->flags = flags;
@@ -237,3 +269,63 @@ SYSCALL_DEFINE1(eventfd, unsigned int, c
return sys_eventfd2(count, 0);
}
+static void eventfd_pollcb_ptqueue(struct file *file, wait_queue_head_t *wqh,
+ poll_table *pt)
+{
+ struct eventfd_pollcb *ecb;
+
+ ecb = container_of(pt, struct eventfd_pollcb, pt);
+
+ add_wait_queue(wqh, &ecb->wait);
+}
+
+/**
+ * eventfd_pollcb_register - Registers a wakeup callback with the eventfd
+ * file. The wakeup callback will be called from
+ * atomic context, and should handle the POLLHUP
+ * event accordingly in order to notice the last
+ * instance of the eventfd descriptor going away.
+ *
+ * @file: [in] Pointer to the eventfd file.
+ * @ecb: [out] Pointer to the eventfd callback structure.
+ * @cbf: [in] Pointer to the wakeup callback function.
+ * @events: [out] Pointer to the events that were ready at the time of the
+ * callback registration.
+ *
+ * Returns: Zero in case of success, or a proper error code.
+ */
+int eventfd_pollcb_register(struct file *file, struct eventfd_pollcb *ecb,
+ wait_queue_func_t cbf, unsigned int *events)
+{
+ struct eventfd_ctx *ctx;
+
+ ctx = file->private_data;
+ if (file->f_op != &eventfd_fops)
+ return -EINVAL;
+
+ init_waitqueue_func_entry(&ecb->wait, cbf);
+ init_poll_funcptr(&ecb->pt, eventfd_pollcb_ptqueue);
+ ecb->ctx = eventfd_get(ctx);
+
+ *events = file->f_op->poll(file, &ecb->pt);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(eventfd_pollcb_register);
+
+/**
+ * eventfd_pollcb_unregister - Unregisters a wakeup callback previously registered
+ * with eventfd_pollcb_register().
+ *
+ * @ecb: [in] Pointer to the eventfd callback structure previously registered with
+ * eventfd_pollcb_register().
+ *
+ * Returns: Nothing.
+ */
+void eventfd_pollcb_unregister(struct eventfd_pollcb *ecb)
+{
+ remove_wait_queue(&ecb->ctx->wqh, &ecb->wait);
+ eventfd_put(ecb->ctx);
+}
+EXPORT_SYMBOL_GPL(eventfd_pollcb_unregister);
+
Index: linux-2.6.mod/include/linux/eventfd.h
===================================================================
--- linux-2.6.mod.orig/include/linux/eventfd.h 2009-06-20 16:25:45.000000000 -0700
+++ linux-2.6.mod/include/linux/eventfd.h 2009-06-21 09:37:12.000000000 -0700
@@ -8,6 +8,20 @@
#ifndef _LINUX_EVENTFD_H
#define _LINUX_EVENTFD_H
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/file.h>
+#include <linux/list.h>
+#include <linux/kref.h>
+
+struct eventfd_ctx;
+
+struct eventfd_pollcb {
+ poll_table pt;
+ struct eventfd_ctx *ctx;
+ wait_queue_t wait;
+};
+
#ifdef CONFIG_EVENTFD
/* For O_CLOEXEC and O_NONBLOCK */
@@ -29,12 +43,22 @@
struct file *eventfd_fget(int fd);
int eventfd_signal(struct file *file, int n);
+int eventfd_pollcb_register(struct file *file, struct eventfd_pollcb *ecb,
+ wait_queue_func_t cbf, unsigned int *events);
+void eventfd_pollcb_unregister(struct eventfd_pollcb *ecb);
#else /* CONFIG_EVENTFD */
#define eventfd_fget(fd) ERR_PTR(-ENOSYS)
static inline int eventfd_signal(struct file *file, int n)
{ return 0; }
+static inline int eventfd_pollcb_register(struct file *file,
+ struct eventfd_pollcb *ecb,
+ wait_queue_func_t cbf,
+ unsigned int *events)
+{ return -ENOSYS; }
+static inline void eventfd_pollcb_unregister(struct eventfd_pollcb *ecb)
+{ }
#endif /* CONFIG_EVENTFD */
--
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