Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757131Ab2BXTOK (ORCPT ); Fri, 24 Feb 2012 14:14:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:4269 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753817Ab2BXTOI (ORCPT ); Fri, 24 Feb 2012 14:14:08 -0500 Date: Fri, 24 Feb 2012 20:07:11 +0100 From: Oleg Nesterov To: Linus Torvalds Cc: Andrew Morton , Davide Libenzi , Eric Dumazet , Greg KH , Jason Baron , Roland McGrath , Eugene Teo , Maxime Bizon , Denys Vlasenko , linux-kernel@vger.kernel.org Subject: [PATCH v2 1/2] epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree() Message-ID: <20120224190711.GB22287@redhat.com> References: <20120222173326.GA7139@redhat.com> <20120222173505.GD7147@redhat.com> <20120223154438.GA4354@redhat.com> <20120224190651.GA22287@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120224190651.GA22287@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5113 Lines: 161 This patch is intentionally incomplete to simplify the review. It ignores ep_unregister_pollwait() which plays with the same wqh. See the next change. epoll assumes that the EPOLL_CTL_ADD'ed file controls everything f_op->poll() needs. In particular it assumes that the wait queue can't go away until eventpoll_release(). This is not true in case of signalfd, the task which does EPOLL_CTL_ADD uses its ->sighand which is not connected to the file. This patch adds the special event, POLLFREE, currently only for epoll. It expects that init_poll_funcptr()'ed hook should do the necessary cleanup. Perhaps it should be defined as EPOLLFREE in eventpoll. __cleanup_sighand() is changed to do wake_up_poll(POLLFREE) if ->signalfd_wqh is not empty, we add the new signalfd_cleanup() helper. ep_poll_callback(POLLFREE) simply does list_del_init(task_list). This make this poll entry inconsistent, but we don't care. If you share epoll fd which contains our sigfd with another process you should blame yourself. signalfd is "really special". I simply do not know how we can define the "right" semantics if it used with epoll. The main problem is, epoll calls signalfd_poll() once to establish the connection with the wait queue, after that signalfd_poll(NULL) returns the different/inconsistent results depending on who does EPOLL_CTL_MOD/signalfd_read/etc. IOW: apart from sigmask, signalfd has nothing to do with the file, it works with the current thread. In short: this patch is the hack which tries to fix the symptoms. It also assumes that nobody can take tasklist_lock under epoll locks, this seems to be true. Note: - we do not have wake_up_all_poll() but wake_up_poll() is fine, poll/epoll doesn't use WQ_FLAG_EXCLUSIVE. - signalfd_cleanup() uses POLLHUP along with POLLFREE, we need a couple of simple changes in eventpoll.c to make sure it can't be "lost". Reported-by: Maxime Bizon Cc: Signed-off-by: Oleg Nesterov --- fs/eventpoll.c | 4 ++++ fs/signalfd.c | 11 +++++++++++ include/asm-generic/poll.h | 2 ++ include/linux/signalfd.h | 5 ++++- kernel/fork.c | 5 ++++- 5 files changed, 25 insertions(+), 2 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index aabdfc3..34bbfc6 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -842,6 +842,10 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k struct epitem *epi = ep_item_from_wait(wait); struct eventpoll *ep = epi->ep; + /* the caller holds eppoll_entry->whead->lock */ + if ((unsigned long)key & POLLFREE) + list_del_init(&wait->task_list); + spin_lock_irqsave(&ep->lock, flags); /* diff --git a/fs/signalfd.c b/fs/signalfd.c index 492465b..79c1eea 100644 --- a/fs/signalfd.c +++ b/fs/signalfd.c @@ -30,6 +30,17 @@ #include #include +void signalfd_cleanup(struct sighand_struct *sighand) +{ + wait_queue_head_t *wqh = &sighand->signalfd_wqh; + + if (likely(!waitqueue_active(wqh))) + return; + + /* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */ + wake_up_poll(wqh, POLLHUP | POLLFREE); +} + struct signalfd_ctx { sigset_t sigmask; }; diff --git a/include/asm-generic/poll.h b/include/asm-generic/poll.h index 44bce83..9ce7f44 100644 --- a/include/asm-generic/poll.h +++ b/include/asm-generic/poll.h @@ -28,6 +28,8 @@ #define POLLRDHUP 0x2000 #endif +#define POLLFREE 0x4000 /* currently only for epoll */ + struct pollfd { int fd; short events; diff --git a/include/linux/signalfd.h b/include/linux/signalfd.h index 3ff4961..247399b 100644 --- a/include/linux/signalfd.h +++ b/include/linux/signalfd.h @@ -61,13 +61,16 @@ static inline void signalfd_notify(struct task_struct *tsk, int sig) wake_up(&tsk->sighand->signalfd_wqh); } +extern void signalfd_cleanup(struct sighand_struct *sighand); + #else /* CONFIG_SIGNALFD */ static inline void signalfd_notify(struct task_struct *tsk, int sig) { } +static inline void signalfd_cleanup(struct sighand_struct *sighand) { } + #endif /* CONFIG_SIGNALFD */ #endif /* __KERNEL__ */ #endif /* _LINUX_SIGNALFD_H */ - diff --git a/kernel/fork.c b/kernel/fork.c index b77fd55..e2cd3e2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -66,6 +66,7 @@ #include #include #include +#include #include #include @@ -935,8 +936,10 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) void __cleanup_sighand(struct sighand_struct *sighand) { - if (atomic_dec_and_test(&sighand->count)) + if (atomic_dec_and_test(&sighand->count)) { + signalfd_cleanup(sighand); kmem_cache_free(sighand_cachep, sighand); + } } -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/