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7741374fa2
commit d80e731eca 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>
77 lines
1.6 KiB
C
77 lines
1.6 KiB
C
/*
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* include/linux/signalfd.h
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*
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* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
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*
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*/
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#ifndef _LINUX_SIGNALFD_H
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#define _LINUX_SIGNALFD_H
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#include <linux/types.h>
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/* For O_CLOEXEC and O_NONBLOCK */
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#include <linux/fcntl.h>
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/* Flags for signalfd4. */
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#define SFD_CLOEXEC O_CLOEXEC
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#define SFD_NONBLOCK O_NONBLOCK
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struct signalfd_siginfo {
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__u32 ssi_signo;
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__s32 ssi_errno;
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__s32 ssi_code;
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__u32 ssi_pid;
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__u32 ssi_uid;
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__s32 ssi_fd;
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__u32 ssi_tid;
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__u32 ssi_band;
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__u32 ssi_overrun;
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__u32 ssi_trapno;
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__s32 ssi_status;
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__s32 ssi_int;
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__u64 ssi_ptr;
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__u64 ssi_utime;
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__u64 ssi_stime;
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__u64 ssi_addr;
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__u16 ssi_addr_lsb;
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/*
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* Pad strcture to 128 bytes. Remember to update the
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* pad size when you add new members. We use a fixed
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* size structure to avoid compatibility problems with
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* future versions, and we leave extra space for additional
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* members. We use fixed size members because this strcture
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* comes out of a read(2) and we really don't want to have
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* a compat on read(2).
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*/
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__u8 __pad[46];
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};
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#ifdef __KERNEL__
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#ifdef CONFIG_SIGNALFD
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/*
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* Deliver the signal to listening signalfd.
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*/
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static inline void signalfd_notify(struct task_struct *tsk, int sig)
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{
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if (unlikely(waitqueue_active(&tsk->sighand->signalfd_wqh)))
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wake_up(&tsk->sighand->signalfd_wqh);
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}
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extern void signalfd_cleanup(struct sighand_struct *sighand);
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#else /* CONFIG_SIGNALFD */
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static inline void signalfd_notify(struct task_struct *tsk, int sig) { }
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static inline void signalfd_cleanup(struct sighand_struct *sighand) { }
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#endif /* CONFIG_SIGNALFD */
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#endif /* __KERNEL__ */
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#endif /* _LINUX_SIGNALFD_H */
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