From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753397AbZFUQ5r (ORCPT ); Sun, 21 Jun 2009 12:57:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752003AbZFUQ5h (ORCPT ); Sun, 21 Jun 2009 12:57:37 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:49610 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751578AbZFUQ5g (ORCPT ); Sun, 21 Jun 2009 12:57:36 -0400 X-AuthUser: davidel@xmailserver.org Date: Sun, 21 Jun 2009 09:51:24 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@makko.or.mcafeemobile.com To: Gregory Haskins cc: mst@redhat.com, kvm@vger.kernel.org, Linux Kernel Mailing List , avi@redhat.com, paulmck@linux.vnet.ibm.com, Ingo Molnar Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions In-Reply-To: <4A3D895C.7020605@novell.com> Message-ID: References: <20090619183534.31118.30934.stgit@dev.haskins.net> <20090619185138.31118.14916.stgit@dev.haskins.net> <4A3C004B.8010706@novell.com> <4A3C07FF.3000406@novell.com> <4A3C44DA.7000503@novell.com> <4A3D895C.7020605@novell.com> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 #include #include +#include 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 +#include +#include +#include +#include + +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 */