2019-05-27 14:55:01 +08:00
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/* SPDX-License-Identifier: GPL-2.0-or-later */
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2005-04-17 06:20:36 +08:00
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/*
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2011-03-31 09:57:33 +08:00
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* include/linux/eventpoll.h ( Efficient event polling implementation )
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2006-06-25 20:48:14 +08:00
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* Copyright (C) 2001,...,2006 Davide Libenzi
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2005-04-17 06:20:36 +08:00
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*
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* Davide Libenzi <davidel@xmailserver.org>
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*/
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#ifndef _LINUX_EVENTPOLL_H
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#define _LINUX_EVENTPOLL_H
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2012-10-13 17:46:48 +08:00
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#include <uapi/linux/eventpoll.h>
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2017-07-13 05:34:28 +08:00
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#include <uapi/linux/kcmp.h>
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2005-04-17 06:20:36 +08:00
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/* Forward declarations to avoid compiler errors */
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struct file;
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#ifdef CONFIG_EPOLL
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2017-07-13 05:34:31 +08:00
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#ifdef CONFIG_CHECKPOINT_RESTORE
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2017-07-13 05:34:28 +08:00
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struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff);
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2017-07-13 05:34:31 +08:00
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#endif
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2017-07-13 05:34:28 +08:00
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2005-04-17 06:20:36 +08:00
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/* Used to release the epoll bits inside the "struct file" */
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void eventpoll_release_file(struct file *file);
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/*
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* This is called from inside fs/file_table.c:__fput() to unlink files
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* from the eventpoll interface. We need to have this facility to cleanup
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* correctly files that are closed without being removed from the eventpoll
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* interface.
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*/
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static inline void eventpoll_release(struct file *file)
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{
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/*
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* Fast check to avoid the get/release of the semaphore. Since
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* we're doing this outside the semaphore lock, it might return
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* false negatives, but we don't care. It'll help in 99.99% of cases
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* to avoid the semaphore lock. False positives simply cannot happen
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* because the file in on the way to be removed and nobody ( but
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* eventpoll ) has still a reference to this file.
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*/
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epoll: take epitem list out of struct file
Move the head of epitem list out of struct file; for epoll ones it's
moved into struct eventpoll (->refs there), for non-epoll - into
the new object (struct epitem_head). In place of ->f_ep_links we
leave a pointer to the list head (->f_ep).
->f_ep is protected by ->f_lock and it's zeroed as soon as the list
of epitems becomes empty (that can happen only in ep_remove() by
now).
The list of files for reverse path check is *not* going through
struct file now - it's a single-linked list going through epitem_head
instances. It's terminated by ERR_PTR(-1) (== EP_UNACTIVE_POINTER),
so the elements of list can be distinguished by head->next != NULL.
epitem_head instances are allocated at ep_insert() time (by
attach_epitem()) and freed either by ep_remove() (if it empties
the set of epitems *and* epitem_head does not belong to the
reverse path check list) or by clear_tfile_check_list() when
the list is emptied (if the set of epitems is empty by that
point). Allocations are done from a separate slab - minimal kmalloc()
size is too large on some architectures.
As the result, we trim struct file _and_ get rid of the games with
temporary file references.
Locking and barriers are interesting (aren't they always); see unlist_file()
and ep_remove() for details. The non-obvious part is that ep_remove() needs
to decide if it will be the one to free the damn thing *before* actually
storing NULL to head->epitems.first - that's what smp_load_acquire is for
in there. unlist_file() lockless path is safe, since we hit it only if
we observe NULL in head->epitems.first and whoever had done that store is
guaranteed to have observed non-NULL in head->next. IOW, their last access
had been the store of NULL into ->epitems.first and we can safely free
the sucker. OTOH, we are under rcu_read_lock() and both epitem and
epitem->file have their freeing RCU-delayed. So if we see non-NULL
->epitems.first, we can grab ->f_lock (all epitems in there share the
same struct file) and safely recheck the emptiness of ->epitems; again,
->next is still non-NULL, so ep_remove() couldn't have freed head yet.
->f_lock serializes us wrt ep_remove(); the rest is trivial.
Note that once head->epitems becomes NULL, nothing can get inserted into
it - the only remaining reference to head after that point is from the
reverse path check list.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-10-02 08:45:51 +08:00
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if (likely(!file->f_ep))
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2005-04-17 06:20:36 +08:00
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return;
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/*
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* The file is being closed while it is still linked to an epoll
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* descriptor. We need to handle this by correctly unlinking it
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* from its containers.
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*/
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eventpoll_release_file(file);
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}
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2020-01-09 06:05:37 +08:00
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int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
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bool nonblock);
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/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
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static inline int ep_op_has_event(int op)
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{
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return op != EPOLL_CTL_DEL;
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}
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2005-04-17 06:20:36 +08:00
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#else
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static inline void eventpoll_release(struct file *file) {}
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#endif
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#endif /* #ifndef _LINUX_EVENTPOLL_H */
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