d80e731eca
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> Cc: <stable@kernel.org> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
39 lines
764 B
C
39 lines
764 B
C
#ifndef __ASM_GENERIC_POLL_H
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#define __ASM_GENERIC_POLL_H
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/* These are specified by iBCS2 */
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#define POLLIN 0x0001
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#define POLLPRI 0x0002
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#define POLLOUT 0x0004
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#define POLLERR 0x0008
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#define POLLHUP 0x0010
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#define POLLNVAL 0x0020
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/* The rest seem to be more-or-less nonstandard. Check them! */
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#define POLLRDNORM 0x0040
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#define POLLRDBAND 0x0080
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#ifndef POLLWRNORM
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#define POLLWRNORM 0x0100
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#endif
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#ifndef POLLWRBAND
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#define POLLWRBAND 0x0200
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#endif
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#ifndef POLLMSG
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#define POLLMSG 0x0400
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#endif
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#ifndef POLLREMOVE
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#define POLLREMOVE 0x1000
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#endif
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#ifndef POLLRDHUP
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#define POLLRDHUP 0x2000
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#endif
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#define POLLFREE 0x4000 /* currently only for epoll */
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struct pollfd {
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int fd;
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short events;
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short revents;
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};
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#endif /* __ASM_GENERIC_POLL_H */
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