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authorOleg Nesterov <oleg@redhat.com>2012-02-24 20:07:11 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-02-29 16:34:34 -0800
commit391d7bfe9ce7a08a700f1ff3dc950a347b23e3cb (patch)
tree9863af1ab73f8e10dc127840ef8b961b03af8bb4 /include
parent809a6d6fddb556579e651ad1fb652d6012f8a102 (diff)
epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()
commit d80e731ecab420ddcb79ee9d0ac427acbc187b4b upstream. 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 <mbizon@freebox.fr> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/poll.h2
-rw-r--r--include/linux/signalfd.h5
2 files changed, 6 insertions, 1 deletions
diff --git a/include/asm-generic/poll.h b/include/asm-generic/poll.h
index 44bce836d350..9ce7f44aebd2 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 3ff4961da9b5..247399b2979a 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 */
-