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OpenCloudOS-Kernel/fs/eventpoll.c

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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* fs/eventpoll.c (Efficient event retrieval implementation)
* Copyright (C) 2001,...,2009 Davide Libenzi
*
* Davide Libenzi <davidel@xmailserver.org>
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/string.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <linux/mount.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/anon_inodes.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <asm/io.h>
#include <asm/mman.h>
#include <linux/atomic.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/compat.h>
#include <linux/rculist.h>
#include <net/busy_poll.h>
/*
* LOCKING:
* There are three level of locking required by epoll :
*
* 1) epmutex (mutex)
* 2) ep->mtx (mutex)
* 3) ep->lock (rwlock)
*
* The acquire order is the one listed above, from 1 to 3.
* We need a rwlock (ep->lock) because we manipulate objects
* from inside the poll callback, that might be triggered from
* a wake_up() that in turn might be called from IRQ context.
* So we can't sleep inside the poll callback and hence we need
* a spinlock. During the event transfer loop (from kernel to
* user space) we could end up sleeping due a copy_to_user(), so
* we need a lock that will allow us to sleep. This lock is a
* mutex (ep->mtx). It is acquired during the event transfer loop,
* during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
* Then we also need a global mutex to serialize eventpoll_release_file()
* and ep_free().
* This mutex is acquired by ep_free() during the epoll file
* cleanup path and it is also acquired by eventpoll_release_file()
* if a file has been pushed inside an epoll set and it is then
* close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL).
* It is also acquired when inserting an epoll fd onto another epoll
* fd. We do this so that we walk the epoll tree and ensure that this
* insertion does not create a cycle of epoll file descriptors, which
* could lead to deadlock. We need a global mutex to prevent two
* simultaneous inserts (A into B and B into A) from racing and
* constructing a cycle without either insert observing that it is
* going to.
* It is necessary to acquire multiple "ep->mtx"es at once in the
* case when one epoll fd is added to another. In this case, we
* always acquire the locks in the order of nesting (i.e. after
* epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired
* before e2->mtx). Since we disallow cycles of epoll file
* descriptors, this ensures that the mutexes are well-ordered. In
* order to communicate this nesting to lockdep, when walking a tree
* of epoll file descriptors, we use the current recursion depth as
* the lockdep subkey.
* It is possible to drop the "ep->mtx" and to use the global
* mutex "epmutex" (together with "ep->lock") to have it working,
* but having "ep->mtx" will make the interface more scalable.
* Events that require holding "epmutex" are very rare, while for
* normal operations the epoll private "ep->mtx" will guarantee
* a better scalability.
*/
/* Epoll private bits inside the event mask */
#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE)
#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT)
#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \
EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE)
/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4
#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
#define EP_UNACTIVE_PTR ((void *) -1L)
#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
struct epoll_filefd {
struct file *file;
int fd;
} __packed;
/*
* Structure used to track possible nested calls, for too deep recursions
* and loop cycles.
*/
struct nested_call_node {
struct list_head llink;
void *cookie;
void *ctx;
};
/*
* This structure is used as collector for nested calls, to check for
* maximum recursion dept and loop cycles.
*/
struct nested_calls {
struct list_head tasks_call_list;
spinlock_t lock;
};
/*
* Each file descriptor added to the eventpoll interface will
* have an entry of this type linked to the "rbr" RB tree.
* Avoid increasing the size of this struct, there can be many thousands
* of these on a server and we do not want this to take another cache line.
*/
struct epitem {
union {
/* RB tree node links this structure to the eventpoll RB tree */
struct rb_node rbn;
/* Used to free the struct epitem */
struct rcu_head rcu;
};
/* List header used to link this structure to the eventpoll ready list */
struct list_head rdllink;
/*
* Works together "struct eventpoll"->ovflist in keeping the
* single linked chain of items.
*/
struct epitem *next;
/* The file descriptor information this item refers to */
struct epoll_filefd ffd;
/* Number of active wait queue attached to poll operations */
int nwait;
/* List containing poll wait queues */
struct list_head pwqlist;
/* The "container" of this item */
struct eventpoll *ep;
/* List header used to link this item to the "struct file" items list */
struct list_head fllink;
/* wakeup_source used when EPOLLWAKEUP is set */
struct wakeup_source __rcu *ws;
/* The structure that describe the interested events and the source fd */
struct epoll_event event;
};
/*
* This structure is stored inside the "private_data" member of the file
* structure and represents the main data structure for the eventpoll
* interface.
*/
struct eventpoll {
/*
* This mutex is used to ensure that files are not removed
* while epoll is using them. This is held during the event
* collection loop, the file cleanup path, the epoll file exit
* code and the ctl operations.
*/
struct mutex mtx;
/* Wait queue used by sys_epoll_wait() */
wait_queue_head_t wq;
/* Wait queue used by file->poll() */
wait_queue_head_t poll_wait;
/* List of ready file descriptors */
struct list_head rdllist;
/* Lock which protects rdllist and ovflist */
rwlock_t lock;
/* RB tree root used to store monitored fd structs */
struct rb_root_cached rbr;
/*
* This is a single linked list that chains all the "struct epitem" that
* happened while transferring ready events to userspace w/out
* holding ->lock.
*/
struct epitem *ovflist;
/* wakeup_source used when ep_scan_ready_list is running */
struct wakeup_source *ws;
/* The user that created the eventpoll descriptor */
struct user_struct *user;
struct file *file;
/* used to optimize loop detection check */
struct list_head visited_list_link;
int visited;
#ifdef CONFIG_NET_RX_BUSY_POLL
/* used to track busy poll napi_id */
unsigned int napi_id;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
/* tracks wakeup nests for lockdep validation */
u8 nests;
#endif
};
/* Wait structure used by the poll hooks */
struct eppoll_entry {
/* List header used to link this structure to the "struct epitem" */
struct list_head llink;
/* The "base" pointer is set to the container "struct epitem" */
struct epitem *base;
/*
* Wait queue item that will be linked to the target file wait
* queue head.
*/
wait_queue_entry_t wait;
/* The wait queue head that linked the "wait" wait queue item */
wait_queue_head_t *whead;
};
/* Wrapper struct used by poll queueing */
struct ep_pqueue {
poll_table pt;
struct epitem *epi;
};
/* Used by the ep_send_events() function as callback private data */
struct ep_send_events_data {
int maxevents;
struct epoll_event __user *events;
int res;
};
/*
* Configuration options available inside /proc/sys/fs/epoll/
*/
/* Maximum number of epoll watched descriptors, per user */
static long max_user_watches __read_mostly;
/*
* This mutex is used to serialize ep_free() and eventpoll_release_file().
*/
static DEFINE_MUTEX(epmutex);
/* Used to check for epoll file descriptor inclusion loops */
static struct nested_calls poll_loop_ncalls;
/* Slab cache used to allocate "struct epitem" */
static struct kmem_cache *epi_cache __read_mostly;
/* Slab cache used to allocate "struct eppoll_entry" */
static struct kmem_cache *pwq_cache __read_mostly;
/* Visited nodes during ep_loop_check(), so we can unset them when we finish */
static LIST_HEAD(visited_list);
/*
* List of files with newly added links, where we may need to limit the number
* of emanating paths. Protected by the epmutex.
*/
static LIST_HEAD(tfile_check_list);
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
static long long_zero;
static long long_max = LONG_MAX;
struct ctl_table epoll_table[] = {
{
.procname = "max_user_watches",
.data = &max_user_watches,
.maxlen = sizeof(max_user_watches),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
.extra1 = &long_zero,
.extra2 = &long_max,
},
{ }
};
#endif /* CONFIG_SYSCTL */
static const struct file_operations eventpoll_fops;
static inline int is_file_epoll(struct file *f)
{
return f->f_op == &eventpoll_fops;
}
/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,
struct file *file, int fd)
{
ffd->file = file;
ffd->fd = fd;
}
/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,
struct epoll_filefd *p2)
{
return (p1->file > p2->file ? +1:
(p1->file < p2->file ? -1 : p1->fd - p2->fd));
}
/* Tells us if the item is currently linked */
static inline int ep_is_linked(struct epitem *epi)
{
return !list_empty(&epi->rdllink);
}
static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p)
{
return container_of(p, struct eppoll_entry, wait);
}
/* Get the "struct epitem" from a wait queue pointer */
static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p)
{
return container_of(p, struct eppoll_entry, wait)->base;
}
/* Get the "struct epitem" from an epoll queue wrapper */
static inline struct epitem *ep_item_from_epqueue(poll_table *p)
{
return container_of(p, struct ep_pqueue, pt)->epi;
}
/* Initialize the poll safe wake up structure */
static void ep_nested_calls_init(struct nested_calls *ncalls)
{
INIT_LIST_HEAD(&ncalls->tasks_call_list);
spin_lock_init(&ncalls->lock);
}
/**
* ep_events_available - Checks if ready events might be available.
*
* @ep: Pointer to the eventpoll context.
*
* Returns: Returns a value different than zero if ready events are available,
* or zero otherwise.
*/
static inline int ep_events_available(struct eventpoll *ep)
{
return !list_empty_careful(&ep->rdllist) ||
READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR;
}
#ifdef CONFIG_NET_RX_BUSY_POLL
static bool ep_busy_loop_end(void *p, unsigned long start_time)
{
struct eventpoll *ep = p;
return ep_events_available(ep) || busy_loop_timeout(start_time);
}
/*
* Busy poll if globally on and supporting sockets found && no events,
* busy loop will return if need_resched or ep_events_available.
*
* we must do our busy polling with irqs enabled
*/
static void ep_busy_loop(struct eventpoll *ep, int nonblock)
{
unsigned int napi_id = READ_ONCE(ep->napi_id);
if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep);
}
static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
{
if (ep->napi_id)
ep->napi_id = 0;
}
/*
* Set epoll busy poll NAPI ID from sk.
*/
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
{
struct eventpoll *ep;
unsigned int napi_id;
struct socket *sock;
struct sock *sk;
int err;
if (!net_busy_loop_on())
return;
sock = sock_from_file(epi->ffd.file, &err);
if (!sock)
return;
sk = sock->sk;
if (!sk)
return;
napi_id = READ_ONCE(sk->sk_napi_id);
ep = epi->ep;
/* Non-NAPI IDs can be rejected
* or
* Nothing to do if we already have this ID
*/
if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id)
return;
/* record NAPI ID for use in next busy poll */
ep->napi_id = napi_id;
}
#else
static inline void ep_busy_loop(struct eventpoll *ep, int nonblock)
{
}
static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
{
}
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
{
}
#endif /* CONFIG_NET_RX_BUSY_POLL */
/**
* ep_call_nested - Perform a bound (possibly) nested call, by checking
* that the recursion limit is not exceeded, and that
* the same nested call (by the meaning of same cookie) is
* no re-entered.
*
* @ncalls: Pointer to the nested_calls structure to be used for this call.
* @nproc: Nested call core function pointer.
* @priv: Opaque data to be passed to the @nproc callback.
* @cookie: Cookie to be used to identify this nested call.
* @ctx: This instance context.
*
* Returns: Returns the code returned by the @nproc callback, or -1 if
* the maximum recursion limit has been exceeded.
*/
static int ep_call_nested(struct nested_calls *ncalls,
int (*nproc)(void *, void *, int), void *priv,
void *cookie, void *ctx)
{
int error, call_nests = 0;
unsigned long flags;
struct list_head *lsthead = &ncalls->tasks_call_list;
struct nested_call_node *tncur;
struct nested_call_node tnode;
spin_lock_irqsave(&ncalls->lock, flags);
/*
* Try to see if the current task is already inside this wakeup call.
* We use a list here, since the population inside this set is always
* very much limited.
*/
list_for_each_entry(tncur, lsthead, llink) {
if (tncur->ctx == ctx &&
(tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) {
/*
* Ops ... loop detected or maximum nest level reached.
* We abort this wake by breaking the cycle itself.
*/
error = -1;
goto out_unlock;
}
}
/* Add the current task and cookie to the list */
tnode.ctx = ctx;
tnode.cookie = cookie;
list_add(&tnode.llink, lsthead);
spin_unlock_irqrestore(&ncalls->lock, flags);
/* Call the nested function */
error = (*nproc)(priv, cookie, call_nests);
/* Remove the current task from the list */
spin_lock_irqsave(&ncalls->lock, flags);
list_del(&tnode.llink);
out_unlock:
spin_unlock_irqrestore(&ncalls->lock, flags);
return error;
}
/*
* As described in commit 0ccf831cb lockdep: annotate epoll
* the use of wait queues used by epoll is done in a very controlled
* manner. Wake ups can nest inside each other, but are never done
* with the same locking. For example:
*
* dfd = socket(...);
* efd1 = epoll_create();
* efd2 = epoll_create();
* epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
* epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
*
* When a packet arrives to the device underneath "dfd", the net code will
* issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
* callback wakeup entry on that queue, and the wake_up() performed by the
* "dfd" net code will end up in ep_poll_callback(). At this point epoll
* (efd1) notices that it may have some event ready, so it needs to wake up
* the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
* that ends up in another wake_up(), after having checked about the
* recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
* avoid stack blasting.
*
* When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
* this special case of epoll.
*/
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
{
struct eventpoll *ep_src;
unsigned long flags;
u8 nests = 0;
/*
* To set the subclass or nesting level for spin_lock_irqsave_nested()
* it might be natural to create a per-cpu nest count. However, since
* we can recurse on ep->poll_wait.lock, and a non-raw spinlock can
* schedule() in the -rt kernel, the per-cpu variable are no longer
* protected. Thus, we are introducing a per eventpoll nest field.
* If we are not being call from ep_poll_callback(), epi is NULL and
* we are at the first level of nesting, 0. Otherwise, we are being
* called from ep_poll_callback() and if a previous wakeup source is
* not an epoll file itself, we are at depth 1 since the wakeup source
* is depth 0. If the wakeup source is a previous epoll file in the
* wakeup chain then we use its nests value and record ours as
* nests + 1. The previous epoll file nests value is stable since its
* already holding its own poll_wait.lock.
*/
if (epi) {
if ((is_file_epoll(epi->ffd.file))) {
ep_src = epi->ffd.file->private_data;
nests = ep_src->nests;
} else {
nests = 1;
}
}
spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests);
ep->nests = nests + 1;
wake_up_locked_poll(&ep->poll_wait, EPOLLIN);
ep->nests = 0;
spin_unlock_irqrestore(&ep->poll_wait.lock, flags);
}
#else
static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi)
{
wake_up_poll(&ep->poll_wait, EPOLLIN);
}
#endif
static void ep_remove_wait_queue(struct eppoll_entry *pwq)
{
wait_queue_head_t *whead;
rcu_read_lock();
/*
* If it is cleared by POLLFREE, it should be rcu-safe.
* If we read NULL we need a barrier paired with
* smp_store_release() in ep_poll_callback(), otherwise
* we rely on whead->lock.
*/
whead = smp_load_acquire(&pwq->whead);
if (whead)
remove_wait_queue(whead, &pwq->wait);
rcu_read_unlock();
}
/*
* This function unregisters poll callbacks from the associated file
* descriptor. Must be called with "mtx" held (or "epmutex" if called from
* ep_free).
*/
static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
{
struct list_head *lsthead = &epi->pwqlist;
struct eppoll_entry *pwq;
while (!list_empty(lsthead)) {
pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
list_del(&pwq->llink);
ep_remove_wait_queue(pwq);
kmem_cache_free(pwq_cache, pwq);
}
}
/* call only when ep->mtx is held */
static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi)
{
return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx));
}
/* call only when ep->mtx is held */
static inline void ep_pm_stay_awake(struct epitem *epi)
{
struct wakeup_source *ws = ep_wakeup_source(epi);
if (ws)
__pm_stay_awake(ws);
}
static inline bool ep_has_wakeup_source(struct epitem *epi)
{
return rcu_access_pointer(epi->ws) ? true : false;
}
/* call when ep->mtx cannot be held (ep_poll_callback) */
static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
{
struct wakeup_source *ws;
rcu_read_lock();
ws = rcu_dereference(epi->ws);
if (ws)
__pm_stay_awake(ws);
rcu_read_unlock();
}
/**
* ep_scan_ready_list - Scans the ready list in a way that makes possible for
* the scan code, to call f_op->poll(). Also allows for
* O(NumReady) performance.
*
* @ep: Pointer to the epoll private data structure.
* @sproc: Pointer to the scan callback.
* @priv: Private opaque data passed to the @sproc callback.
* @depth: The current depth of recursive f_op->poll calls.
* @ep_locked: caller already holds ep->mtx
*
* Returns: The same integer error code returned by the @sproc callback.
*/
static __poll_t ep_scan_ready_list(struct eventpoll *ep,
__poll_t (*sproc)(struct eventpoll *,
struct list_head *, void *),
void *priv, int depth, bool ep_locked)
{
__poll_t res;
struct epitem *epi, *nepi;
LIST_HEAD(txlist);
lockdep_assert_irqs_enabled();
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() and epoll_ctl().
*/
if (!ep_locked)
mutex_lock_nested(&ep->mtx, depth);
/*
* Steal the ready list, and re-init the original one to the
* empty list. Also, set ep->ovflist to NULL so that events
* happening while looping w/out locks, are not lost. We cannot
* have the poll callback to queue directly on ep->rdllist,
* because we want the "sproc" callback to be able to do it
* in a lockless way.
*/
write_lock_irq(&ep->lock);
list_splice_init(&ep->rdllist, &txlist);
WRITE_ONCE(ep->ovflist, NULL);
write_unlock_irq(&ep->lock);
/*
* Now call the callback function.
*/
res = (*sproc)(ep, &txlist, priv);
write_lock_irq(&ep->lock);
/*
* During the time we spent inside the "sproc" callback, some
* other events might have been queued by the poll callback.
* We re-insert them inside the main ready-list here.
*/
for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL;
nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
/*
* We need to check if the item is already in the list.
* During the "sproc" callback execution time, items are
* queued into ->ovflist but the "txlist" might already
* contain them, and the list_splice() below takes care of them.
*/
if (!ep_is_linked(epi)) {
/*
* ->ovflist is LIFO, so we have to reverse it in order
* to keep in FIFO.
*/
list_add(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
}
}
/*
* We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
* releasing the lock, events will be queued in the normal way inside
* ep->rdllist.
*/
WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR);
/*
* Quickly re-inject items left on "txlist".
*/
list_splice(&txlist, &ep->rdllist);
__pm_relax(ep->ws);
write_unlock_irq(&ep->lock);
if (!ep_locked)
mutex_unlock(&ep->mtx);
return res;
}
static void epi_rcu_free(struct rcu_head *head)
{
struct epitem *epi = container_of(head, struct epitem, rcu);
kmem_cache_free(epi_cache, epi);
}
/*
* Removes a "struct epitem" from the eventpoll RB tree and deallocates
* all the associated resources. Must be called with "mtx" held.
*/
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
struct file *file = epi->ffd.file;
lockdep_assert_irqs_enabled();
/*
* Removes poll wait queue hooks.
*/
ep_unregister_pollwait(ep, epi);
/* Remove the current item from the list of epoll hooks */
spin_lock(&file->f_lock);
list_del_rcu(&epi->fllink);
spin_unlock(&file->f_lock);
rb_erase_cached(&epi->rbn, &ep->rbr);
write_lock_irq(&ep->lock);
if (ep_is_linked(epi))
list_del_init(&epi->rdllink);
write_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi));
/*
* At this point it is safe to free the eventpoll item. Use the union
* field epi->rcu, since we are trying to minimize the size of
* 'struct epitem'. The 'rbn' field is no longer in use. Protected by
* ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
* use of the rbn field.
*/
call_rcu(&epi->rcu, epi_rcu_free);
atomic_long_dec(&ep->user->epoll_watches);
return 0;
}
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
struct epitem *epi;
/* We need to release all tasks waiting for these file */
if (waitqueue_active(&ep->poll_wait))
ep_poll_safewake(ep, NULL);
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() while we're freeing the "struct eventpoll".
* We do not need to hold "ep->mtx" here because the epoll file
* is on the way to be removed and no one has references to it
* anymore. The only hit might come from eventpoll_release_file() but
* holding "epmutex" is sufficient here.
*/
mutex_lock(&epmutex);
/*
* Walks through the whole tree by unregistering poll callbacks.
*/
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_unregister_pollwait(ep, epi);
cond_resched();
}
/*
* Walks through the whole tree by freeing each "struct epitem". At this
* point we are sure no poll callbacks will be lingering around, and also by
* holding "epmutex" we can be sure that no file cleanup code will hit
* us during this operation. So we can avoid the lock on "ep->lock".
* We do not need to lock ep->mtx, either, we only do it to prevent
* a lockdep warning.
*/
mutex_lock(&ep->mtx);
while ((rbp = rb_first_cached(&ep->rbr)) != NULL) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_remove(ep, epi);
cond_resched();
}
mutex_unlock(&ep->mtx);
mutex_unlock(&epmutex);
mutex_destroy(&ep->mtx);
free_uid(ep->user);
wakeup_source_unregister(ep->ws);
kfree(ep);
}
static int ep_eventpoll_release(struct inode *inode, struct file *file)
{
struct eventpoll *ep = file->private_data;
if (ep)
ep_free(ep);
return 0;
}
static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv);
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
poll_table *pt);
/*
* Differs from ep_eventpoll_poll() in that internal callers already have
* the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
* is correctly annotated.
*/
static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
int depth)
{
struct eventpoll *ep;
bool locked;
pt->_key = epi->event.events;
if (!is_file_epoll(epi->ffd.file))
return vfs_poll(epi->ffd.file, pt) & epi->event.events;
ep = epi->ffd.file->private_data;
poll_wait(epi->ffd.file, &ep->poll_wait, pt);
locked = pt && (pt->_qproc == ep_ptable_queue_proc);
return ep_scan_ready_list(epi->ffd.file->private_data,
ep_read_events_proc, &depth, depth,
locked) & epi->event.events;
}
static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv)
{
struct epitem *epi, *tmp;
poll_table pt;
int depth = *(int *)priv;
init_poll_funcptr(&pt, NULL);
depth++;
list_for_each_entry_safe(epi, tmp, head, rdllink) {
if (ep_item_poll(epi, &pt, depth)) {
return EPOLLIN | EPOLLRDNORM;
} else {
/*
* Item has been dropped into the ready list by the poll
* callback, but it's not actually ready, as far as
* caller requested events goes. We can remove it here.
*/
__pm_relax(ep_wakeup_source(epi));
list_del_init(&epi->rdllink);
}
}
return 0;
}
static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
{
struct eventpoll *ep = file->private_data;
int depth = 0;
/* Insert inside our poll wait queue */
poll_wait(file, &ep->poll_wait, wait);
/*
* Proceed to find out if wanted events are really available inside
* the ready list.
*/
return ep_scan_ready_list(ep, ep_read_events_proc,
&depth, depth, false);
}
#ifdef CONFIG_PROC_FS
static void ep_show_fdinfo(struct seq_file *m, struct file *f)
{
struct eventpoll *ep = f->private_data;
struct rb_node *rbp;
mutex_lock(&ep->mtx);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
struct epitem *epi = rb_entry(rbp, struct epitem, rbn);
struct inode *inode = file_inode(epi->ffd.file);
seq_printf(m, "tfd: %8d events: %8x data: %16llx "
" pos:%lli ino:%lx sdev:%x\n",
epi->ffd.fd, epi->event.events,
(long long)epi->event.data,
(long long)epi->ffd.file->f_pos,
inode->i_ino, inode->i_sb->s_dev);
if (seq_has_overflowed(m))
break;
}
mutex_unlock(&ep->mtx);
}
#endif
/* File callbacks that implement the eventpoll file behaviour */
static const struct file_operations eventpoll_fops = {
#ifdef CONFIG_PROC_FS
.show_fdinfo = ep_show_fdinfo,
#endif
.release = ep_eventpoll_release,
.poll = ep_eventpoll_poll,
.llseek = noop_llseek,
};
/*
* This is called from eventpoll_release() to unlink files from the eventpoll
* interface. We need to have this facility to cleanup correctly files that are
* closed without being removed from the eventpoll interface.
*/
void eventpoll_release_file(struct file *file)
{
struct eventpoll *ep;
struct epitem *epi, *next;
/*
* We don't want to get "file->f_lock" because it is not
* necessary. It is not necessary because we're in the "struct file"
* cleanup path, and this means that no one is using this file anymore.
* So, for example, epoll_ctl() cannot hit here since if we reach this
* point, the file counter already went to zero and fget() would fail.
* The only hit might come from ep_free() but by holding the mutex
* will correctly serialize the operation. We do need to acquire
* "ep->mtx" after "epmutex" because ep_remove() requires it when called
* from anywhere but ep_free().
*
* Besides, ep_remove() acquires the lock, so we can't hold it here.
*/
mutex_lock(&epmutex);
list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) {
ep = epi->ep;
mutex_lock_nested(&ep->mtx, 0);
ep_remove(ep, epi);
mutex_unlock(&ep->mtx);
}
mutex_unlock(&epmutex);
}
static int ep_alloc(struct eventpoll **pep)
{
int error;
struct user_struct *user;
struct eventpoll *ep;
user = get_current_user();
error = -ENOMEM;
ep = kzalloc(sizeof(*ep), GFP_KERNEL);
if (unlikely(!ep))
goto free_uid;
mutex_init(&ep->mtx);
rwlock_init(&ep->lock);
init_waitqueue_head(&ep->wq);
init_waitqueue_head(&ep->poll_wait);
INIT_LIST_HEAD(&ep->rdllist);
ep->rbr = RB_ROOT_CACHED;
ep->ovflist = EP_UNACTIVE_PTR;
ep->user = user;
*pep = ep;
return 0;
free_uid:
free_uid(user);
return error;
}
/*
* Search the file inside the eventpoll tree. The RB tree operations
* are protected by the "mtx" mutex, and ep_find() must be called with
* "mtx" held.
*/
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{
int kcmp;
struct rb_node *rbp;
struct epitem *epi, *epir = NULL;
struct epoll_filefd ffd;
ep_set_ffd(&ffd, file, fd);
for (rbp = ep->rbr.rb_root.rb_node; rbp; ) {
epi = rb_entry(rbp, struct epitem, rbn);
kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
if (kcmp > 0)
rbp = rbp->rb_right;
else if (kcmp < 0)
rbp = rbp->rb_left;
else {
epir = epi;
break;
}
}
return epir;
}
#ifdef CONFIG_CHECKPOINT_RESTORE
static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff)
{
struct rb_node *rbp;
struct epitem *epi;
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
if (epi->ffd.fd == tfd) {
if (toff == 0)
return epi;
else
toff--;
}
cond_resched();
}
return NULL;
}
struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
unsigned long toff)
{
struct file *file_raw;
struct eventpoll *ep;
struct epitem *epi;
if (!is_file_epoll(file))
return ERR_PTR(-EINVAL);
ep = file->private_data;
mutex_lock(&ep->mtx);
epi = ep_find_tfd(ep, tfd, toff);
if (epi)
file_raw = epi->ffd.file;
else
file_raw = ERR_PTR(-ENOENT);
mutex_unlock(&ep->mtx);
return file_raw;
}
#endif /* CONFIG_CHECKPOINT_RESTORE */
/**
* Adds a new entry to the tail of the list in a lockless way, i.e.
* multiple CPUs are allowed to call this function concurrently.
*
* Beware: it is necessary to prevent any other modifications of the
* existing list until all changes are completed, in other words
* concurrent list_add_tail_lockless() calls should be protected
* with a read lock, where write lock acts as a barrier which
* makes sure all list_add_tail_lockless() calls are fully
* completed.
*
* Also an element can be locklessly added to the list only in one
* direction i.e. either to the tail either to the head, otherwise
* concurrent access will corrupt the list.
*
* Returns %false if element has been already added to the list, %true
* otherwise.
*/
static inline bool list_add_tail_lockless(struct list_head *new,
struct list_head *head)
{
struct list_head *prev;
/*
* This is simple 'new->next = head' operation, but cmpxchg()
* is used in order to detect that same element has been just
* added to the list from another CPU: the winner observes
* new->next == new.
*/
if (cmpxchg(&new->next, new, head) != new)
return false;
/*
* Initially ->next of a new element must be updated with the head
* (we are inserting to the tail) and only then pointers are atomically
* exchanged. XCHG guarantees memory ordering, thus ->next should be
* updated before pointers are actually swapped and pointers are
* swapped before prev->next is updated.
*/
prev = xchg(&head->prev, new);
/*
* It is safe to modify prev->next and new->prev, because a new element
* is added only to the tail and new->next is updated before XCHG.
*/
prev->next = new;
new->prev = prev;
return true;
}
/**
* Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
* i.e. multiple CPUs are allowed to call this function concurrently.
*
* Returns %false if epi element has been already chained, %true otherwise.
*/
static inline bool chain_epi_lockless(struct epitem *epi)
{
struct eventpoll *ep = epi->ep;
/* Fast preliminary check */
if (epi->next != EP_UNACTIVE_PTR)
return false;
/* Check that the same epi has not been just chained from another CPU */
if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
return false;
/* Atomically exchange tail */
epi->next = xchg(&ep->ovflist, epi);
return true;
}
/*
* This is the callback that is passed to the wait queue wakeup
* mechanism. It is called by the stored file descriptors when they
* have events to report.
*
* This callback takes a read lock in order not to content with concurrent
* events from another file descriptors, thus all modifications to ->rdllist
* or ->ovflist are lockless. Read lock is paired with the write lock from
* ep_scan_ready_list(), which stops all list modifications and guarantees
* that lists state is seen correctly.
*
* Another thing worth to mention is that ep_poll_callback() can be called
* concurrently for the same @epi from different CPUs if poll table was inited
* with several wait queues entries. Plural wakeup from different CPUs of a
* single wait queue is serialized by wq.lock, but the case when multiple wait
* queues are used should be detected accordingly. This is detected using
* cmpxchg() operation.
*/
static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
int pwake = 0;
struct epitem *epi = ep_item_from_wait(wait);
struct eventpoll *ep = epi->ep;
__poll_t pollflags = key_to_poll(key);
unsigned long flags;
int ewake = 0;
read_lock_irqsave(&ep->lock, flags);
ep_set_busy_poll_napi_id(epi);
/*
* If the event mask does not contain any poll(2) event, we consider the
* descriptor to be disabled. This condition is likely the effect of the
* EPOLLONESHOT bit that disables the descriptor when an event is received,
* until the next EPOLL_CTL_MOD will be issued.
*/
if (!(epi->event.events & ~EP_PRIVATE_BITS))
goto out_unlock;
/*
* Check the events coming with the callback. At this stage, not
* every device reports the events in the "key" parameter of the
* callback. We need to be able to handle both cases here, hence the
* test for "key" != NULL before the event match test.
*/
if (pollflags && !(pollflags & epi->event.events))
goto out_unlock;
/*
* If we are transferring events to userspace, we can hold no locks
* (because we're accessing user memory, and because of linux f_op->poll()
* semantics). All the events that happen during that period of time are
* chained in ep->ovflist and requeued later on.
*/
if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
if (chain_epi_lockless(epi))
ep_pm_stay_awake_rcu(epi);
} else if (!ep_is_linked(epi)) {
/* In the usual case, add event to ready list. */
if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist))
ep_pm_stay_awake_rcu(epi);
}
/*
* Wake up ( if active ) both the eventpoll wait list and the ->poll()
* wait list.
*/
if (waitqueue_active(&ep->wq)) {
if ((epi->event.events & EPOLLEXCLUSIVE) &&
!(pollflags & POLLFREE)) {
switch (pollflags & EPOLLINOUT_BITS) {
case EPOLLIN:
if (epi->event.events & EPOLLIN)
ewake = 1;
break;
case EPOLLOUT:
if (epi->event.events & EPOLLOUT)
ewake = 1;
break;
case 0:
ewake = 1;
break;
}
}
wake_up(&ep->wq);
}
if (waitqueue_active(&ep->poll_wait))
pwake++;
out_unlock:
read_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(ep, epi);
if (!(epi->event.events & EPOLLEXCLUSIVE))
ewake = 1;
if (pollflags & POLLFREE) {
/*
* If we race with ep_remove_wait_queue() it can miss
* ->whead = NULL and do another remove_wait_queue() after
* us, so we can't use __remove_wait_queue().
*/
list_del_init(&wait->entry);
/*
* ->whead != NULL protects us from the race with ep_free()
* or ep_remove(), ep_remove_wait_queue() takes whead->lock
* held by the caller. Once we nullify it, nothing protects
* ep/epi or even wait.
*/
smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL);
}
return ewake;
}
/*
* This is the callback that is used to add our wait queue to the
* target file wakeup lists.
*/
static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
poll_table *pt)
{
struct epitem *epi = ep_item_from_epqueue(pt);
struct eppoll_entry *pwq;
if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) {
init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
pwq->whead = whead;
pwq->base = epi;
if (epi->event.events & EPOLLEXCLUSIVE)
add_wait_queue_exclusive(whead, &pwq->wait);
else
add_wait_queue(whead, &pwq->wait);
list_add_tail(&pwq->llink, &epi->pwqlist);
epi->nwait++;
} else {
/* We have to signal that an error occurred */
epi->nwait = -1;
}
}
static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
{
int kcmp;
struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL;
struct epitem *epic;
bool leftmost = true;
while (*p) {
parent = *p;
epic = rb_entry(parent, struct epitem, rbn);
kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd);
if (kcmp > 0) {
p = &parent->rb_right;
leftmost = false;
} else
p = &parent->rb_left;
}
rb_link_node(&epi->rbn, parent, p);
rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost);
}
#define PATH_ARR_SIZE 5
/*
* These are the number paths of length 1 to 5, that we are allowing to emanate
* from a single file of interest. For example, we allow 1000 paths of length
* 1, to emanate from each file of interest. This essentially represents the
* potential wakeup paths, which need to be limited in order to avoid massive
* uncontrolled wakeup storms. The common use case should be a single ep which
* is connected to n file sources. In this case each file source has 1 path
* of length 1. Thus, the numbers below should be more than sufficient. These
* path limits are enforced during an EPOLL_CTL_ADD operation, since a modify
* and delete can't add additional paths. Protected by the epmutex.
*/
static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 };
static int path_count[PATH_ARR_SIZE];
static int path_count_inc(int nests)
{
/* Allow an arbitrary number of depth 1 paths */
if (nests == 0)
return 0;
if (++path_count[nests] > path_limits[nests])
return -1;
return 0;
}
static void path_count_init(void)
{
int i;
for (i = 0; i < PATH_ARR_SIZE; i++)
path_count[i] = 0;
}
static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
{
int error = 0;
struct file *file = priv;
struct file *child_file;
struct epitem *epi;
/* CTL_DEL can remove links here, but that can't increase our count */
rcu_read_lock();
list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
child_file = epi->ep->file;
if (is_file_epoll(child_file)) {
if (list_empty(&child_file->f_ep_links)) {
if (path_count_inc(call_nests)) {
error = -1;
break;
}
} else {
error = ep_call_nested(&poll_loop_ncalls,
reverse_path_check_proc,
child_file, child_file,
current);
}
if (error != 0)
break;
} else {
printk(KERN_ERR "reverse_path_check_proc: "
"file is not an ep!\n");
}
}
rcu_read_unlock();
return error;
}
/**
* reverse_path_check - The tfile_check_list is list of file *, which have
* links that are proposed to be newly added. We need to
* make sure that those added links don't add too many
* paths such that we will spend all our time waking up
* eventpoll objects.
*
* Returns: Returns zero if the proposed links don't create too many paths,
* -1 otherwise.
*/
static int reverse_path_check(void)
{
int error = 0;
struct file *current_file;
/* let's call this for all tfiles */
list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
path_count_init();
error = ep_call_nested(&poll_loop_ncalls,
reverse_path_check_proc, current_file,
current_file, current);
if (error)
break;
}
return error;
}
static int ep_create_wakeup_source(struct epitem *epi)
{
const char *name;
struct wakeup_source *ws;
if (!epi->ep->ws) {
epi->ep->ws = wakeup_source_register(NULL, "eventpoll");
if (!epi->ep->ws)
return -ENOMEM;
}
name = epi->ffd.file->f_path.dentry->d_name.name;
ws = wakeup_source_register(NULL, name);
if (!ws)
return -ENOMEM;
rcu_assign_pointer(epi->ws, ws);
return 0;
}
/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */
static noinline void ep_destroy_wakeup_source(struct epitem *epi)
{
struct wakeup_source *ws = ep_wakeup_source(epi);
RCU_INIT_POINTER(epi->ws, NULL);
/*
* wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is
* used internally by wakeup_source_remove, too (called by
* wakeup_source_unregister), so we cannot use call_rcu
*/
synchronize_rcu();
wakeup_source_unregister(ws);
}
/*
* Must be called with "mtx" held.
*/
static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
struct file *tfile, int fd, int full_check)
{
int error, pwake = 0;
__poll_t revents;
long user_watches;
struct epitem *epi;
struct ep_pqueue epq;
lockdep_assert_irqs_enabled();
user_watches = atomic_long_read(&ep->user->epoll_watches);
if (unlikely(user_watches >= max_user_watches))
return -ENOSPC;
if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL)))
return -ENOMEM;
/* Item initialization follow here ... */
INIT_LIST_HEAD(&epi->rdllink);
INIT_LIST_HEAD(&epi->fllink);
INIT_LIST_HEAD(&epi->pwqlist);
epi->ep = ep;
ep_set_ffd(&epi->ffd, tfile, fd);
epi->event = *event;
epi->nwait = 0;
epi->next = EP_UNACTIVE_PTR;
if (epi->event.events & EPOLLWAKEUP) {
error = ep_create_wakeup_source(epi);
if (error)
goto error_create_wakeup_source;
} else {
RCU_INIT_POINTER(epi->ws, NULL);
}
/* Initialize the poll table using the queue callback */
epq.epi = epi;
init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
/*
* Attach the item to the poll hooks and get current event bits.
* We can safely use the file* here because its usage count has
* been increased by the caller of this function. Note that after
* this operation completes, the poll callback can start hitting
* the new item.
*/
revents = ep_item_poll(epi, &epq.pt, 1);
/*
* We have to check if something went wrong during the poll wait queue
* install process. Namely an allocation for a wait queue failed due
* high memory pressure.
*/
error = -ENOMEM;
if (epi->nwait < 0)
goto error_unregister;
/* Add the current item to the list of active epoll hook for this file */
spin_lock(&tfile->f_lock);
list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
spin_unlock(&tfile->f_lock);
/*
* Add the current item to the RB tree. All RB tree operations are
* protected by "mtx", and ep_insert() is called with "mtx" held.
*/
ep_rbtree_insert(ep, epi);
/* now check if we've created too many backpaths */
error = -EINVAL;
if (full_check && reverse_path_check())
goto error_remove_epi;
/* We have to drop the new item inside our item list to keep track of it */
write_lock_irq(&ep->lock);
/* record NAPI ID of new item if present */
ep_set_busy_poll_napi_id(epi);
/* If the file is already "ready" we drop it inside the ready list */
if (revents && !ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irq(&ep->lock);
atomic_long_inc(&ep->user->epoll_watches);
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(ep, NULL);
return 0;
error_remove_epi:
spin_lock(&tfile->f_lock);
list_del_rcu(&epi->fllink);
spin_unlock(&tfile->f_lock);
rb_erase_cached(&epi->rbn, &ep->rbr);
error_unregister:
ep_unregister_pollwait(ep, epi);
/*
* We need to do this because an event could have been arrived on some
* allocated wait queue. Note that we don't care about the ep->ovflist
* list, since that is used/cleaned only inside a section bound by "mtx".
* And ep_insert() is called with "mtx" held.
*/
write_lock_irq(&ep->lock);
if (ep_is_linked(epi))
list_del_init(&epi->rdllink);
write_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi));
error_create_wakeup_source:
kmem_cache_free(epi_cache, epi);
return error;
}
/*
* Modify the interest event mask by dropping an event if the new mask
* has a match in the current file status. Must be called with "mtx" held.
*/
static int ep_modify(struct eventpoll *ep, struct epitem *epi,
const struct epoll_event *event)
{
int pwake = 0;
poll_table pt;
lockdep_assert_irqs_enabled();
init_poll_funcptr(&pt, NULL);
/*
* Set the new event interest mask before calling f_op->poll();
* otherwise we might miss an event that happens between the
* f_op->poll() call and the new event set registering.
*/
epi->event.events = event->events; /* need barrier below */
epi->event.data = event->data; /* protected by mtx */
if (epi->event.events & EPOLLWAKEUP) {
if (!ep_has_wakeup_source(epi))
ep_create_wakeup_source(epi);
} else if (ep_has_wakeup_source(epi)) {
ep_destroy_wakeup_source(epi);
}
/*
* The following barrier has two effects:
*
* 1) Flush epi changes above to other CPUs. This ensures
* we do not miss events from ep_poll_callback if an
* event occurs immediately after we call f_op->poll().
* We need this because we did not take ep->lock while
* changing epi above (but ep_poll_callback does take
* ep->lock).
*
* 2) We also need to ensure we do not miss _past_ events
* when calling f_op->poll(). This barrier also
* pairs with the barrier in wq_has_sleeper (see
* comments for wq_has_sleeper).
*
* This barrier will now guarantee ep_poll_callback or f_op->poll
* (or both) will notice the readiness of an item.
*/
smp_mb();
/*
* Get current event bits. We can safely use the file* here because
* its usage count has been increased by the caller of this function.
* If the item is "hot" and it is not registered inside the ready
* list, push it inside.
*/
if (ep_item_poll(epi, &pt, 1)) {
write_lock_irq(&ep->lock);
if (!ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
wake_up(&ep->wq);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irq(&ep->lock);
}
/* We have to call this outside the lock */
if (pwake)
ep_poll_safewake(ep, NULL);
return 0;
}
static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv)
{
struct ep_send_events_data *esed = priv;
__poll_t revents;
struct epitem *epi, *tmp;
struct epoll_event __user *uevent = esed->events;
struct wakeup_source *ws;
poll_table pt;
init_poll_funcptr(&pt, NULL);
esed->res = 0;
/*
* We can loop without lock because we are passed a task private list.
* Items cannot vanish during the loop because ep_scan_ready_list() is
* holding "mtx" during this call.
*/
lockdep_assert_held(&ep->mtx);
list_for_each_entry_safe(epi, tmp, head, rdllink) {
if (esed->res >= esed->maxevents)
break;
/*
* Activate ep->ws before deactivating epi->ws to prevent
* triggering auto-suspend here (in case we reactive epi->ws
* below).
*
* This could be rearranged to delay the deactivation of epi->ws
* instead, but then epi->ws would temporarily be out of sync
* with ep_is_linked().
*/
ws = ep_wakeup_source(epi);
if (ws) {
if (ws->active)
__pm_stay_awake(ep->ws);
__pm_relax(ws);
}
list_del_init(&epi->rdllink);
/*
* If the event mask intersect the caller-requested one,
* deliver the event to userspace. Again, ep_scan_ready_list()
* is holding ep->mtx, so no operations coming from userspace
* can change the item.
*/
revents = ep_item_poll(epi, &pt, 1);
if (!revents)
continue;
if (__put_user(revents, &uevent->events) ||
__put_user(epi->event.data, &uevent->data)) {
list_add(&epi->rdllink, head);
ep_pm_stay_awake(epi);
if (!esed->res)
esed->res = -EFAULT;
return 0;
}
esed->res++;
uevent++;
if (epi->event.events & EPOLLONESHOT)
epi->event.events &= EP_PRIVATE_BITS;
else if (!(epi->event.events & EPOLLET)) {
/*
* If this file has been added with Level
* Trigger mode, we need to insert back inside
* the ready list, so that the next call to
* epoll_wait() will check again the events
* availability. At this point, no one can insert
* into ep->rdllist besides us. The epoll_ctl()
* callers are locked out by
* ep_scan_ready_list() holding "mtx" and the
* poll callback will queue them in ep->ovflist.
*/
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
}
}
return 0;
}
static int ep_send_events(struct eventpoll *ep,
struct epoll_event __user *events, int maxevents)
{
struct ep_send_events_data esed;
esed.maxevents = maxevents;
esed.events = events;
ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
return esed.res;
}
static inline struct timespec64 ep_set_mstimeout(long ms)
{
struct timespec64 now, ts = {
.tv_sec = ms / MSEC_PER_SEC,
.tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC),
};
ktime_get_ts64(&now);
return timespec64_add_safe(now, ts);
}
/**
* ep_poll - Retrieves ready events, and delivers them to the caller supplied
* event buffer.
*
* @ep: Pointer to the eventpoll context.
* @events: Pointer to the userspace buffer where the ready events should be
* stored.
* @maxevents: Size (in terms of number of events) of the caller event buffer.
* @timeout: Maximum timeout for the ready events fetch operation, in
* milliseconds. If the @timeout is zero, the function will not block,
* while if the @timeout is less than zero, the function will block
* until at least one event has been retrieved (or an error
* occurred).
*
* Returns: Returns the number of ready events which have been fetched, or an
* error code, in case of error.
*/
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, long timeout)
{
int res = 0, eavail, timed_out = 0;
u64 slack = 0;
wait_queue_entry_t wait;
ktime_t expires, *to = NULL;
lockdep_assert_irqs_enabled();
if (timeout > 0) {
struct timespec64 end_time = ep_set_mstimeout(timeout);
slack = select_estimate_accuracy(&end_time);
to = &expires;
*to = timespec64_to_ktime(end_time);
} else if (timeout == 0) {
/*
* Avoid the unnecessary trip to the wait queue loop, if the
* caller specified a non blocking operation. We still need
* lock because we could race and not see an epi being added
* to the ready list while in irq callback. Thus incorrectly
* returning 0 back to userspace.
*/
timed_out = 1;
write_lock_irq(&ep->lock);
eavail = ep_events_available(ep);
write_unlock_irq(&ep->lock);
goto send_events;
}
fetch_events:
if (!ep_events_available(ep))
ep_busy_loop(ep, timed_out);
eavail = ep_events_available(ep);
if (eavail)
goto send_events;
/*
* Busy poll timed out. Drop NAPI ID for now, we can add
* it back in when we have moved a socket with a valid NAPI
* ID onto the ready list.
*/
ep_reset_busy_poll_napi_id(ep);
do {
/*
* Internally init_wait() uses autoremove_wake_function(),
* thus wait entry is removed from the wait queue on each
* wakeup. Why it is important? In case of several waiters
* each new wakeup will hit the next waiter, giving it the
* chance to harvest new event. Otherwise wakeup can be
* lost. This is also good performance-wise, because on
* normal wakeup path no need to call __remove_wait_queue()
* explicitly, thus ep->lock is not taken, which halts the
* event delivery.
*/
init_wait(&wait);
write_lock_irq(&ep->lock);
/*
* Barrierless variant, waitqueue_active() is called under
* the same lock on wakeup ep_poll_callback() side, so it
* is safe to avoid an explicit barrier.
*/
__set_current_state(TASK_INTERRUPTIBLE);
/*
* Do the final check under the lock. ep_scan_ready_list()
* plays with two lists (->rdllist and ->ovflist) and there
* is always a race when both lists are empty for short
* period of time although events are pending, so lock is
* important.
*/
eavail = ep_events_available(ep);
if (!eavail) {
if (signal_pending(current))
res = -EINTR;
else
__add_wait_queue_exclusive(&ep->wq, &wait);
}
write_unlock_irq(&ep->lock);
if (eavail || res)
break;
if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) {
timed_out = 1;
break;
}
/* We were woken up, thus go and try to harvest some events */
eavail = 1;
} while (0);
__set_current_state(TASK_RUNNING);
if (!list_empty_careful(&wait.entry)) {
write_lock_irq(&ep->lock);
__remove_wait_queue(&ep->wq, &wait);
write_unlock_irq(&ep->lock);
}
send_events:
if (fatal_signal_pending(current)) {
/*
* Always short-circuit for fatal signals to allow
* threads to make a timely exit without the chance of
* finding more events available and fetching
* repeatedly.
*/
res = -EINTR;
}
/*
* Try to transfer events to user space. In case we get 0 events and
* there's still timeout left over, we go trying again in search of
* more luck.
*/
if (!res && eavail &&
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
goto fetch_events;
return res;
}
/**
* ep_loop_check_proc - Callback function to be passed to the @ep_call_nested()
* API, to verify that adding an epoll file inside another
* epoll structure, does not violate the constraints, in
* terms of closed loops, or too deep chains (which can
* result in excessive stack usage).
*
* @priv: Pointer to the epoll file to be currently checked.
* @cookie: Original cookie for this call. This is the top-of-the-chain epoll
* data structure pointer.
* @call_nests: Current dept of the @ep_call_nested() call stack.
*
* Returns: Returns zero if adding the epoll @file inside current epoll
* structure @ep does not violate the constraints, or -1 otherwise.
*/
static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
{
int error = 0;
struct file *file = priv;
struct eventpoll *ep = file->private_data;
struct eventpoll *ep_tovisit;
struct rb_node *rbp;
struct epitem *epi;
mutex_lock_nested(&ep->mtx, call_nests + 1);
ep->visited = 1;
list_add(&ep->visited_list_link, &visited_list);
for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) {
epi = rb_entry(rbp, struct epitem, rbn);
if (unlikely(is_file_epoll(epi->ffd.file))) {
ep_tovisit = epi->ffd.file->private_data;
if (ep_tovisit->visited)
continue;
error = ep_call_nested(&poll_loop_ncalls,
ep_loop_check_proc, epi->ffd.file,
ep_tovisit, current);
if (error != 0)
break;
} else {
/*
* If we've reached a file that is not associated with
* an ep, then we need to check if the newly added
* links are going to add too many wakeup paths. We do
* this by adding it to the tfile_check_list, if it's
* not already there, and calling reverse_path_check()
* during ep_insert().
*/
if (list_empty(&epi->ffd.file->f_tfile_llink)) {
if (get_file_rcu(epi->ffd.file))
list_add(&epi->ffd.file->f_tfile_llink,
&tfile_check_list);
}
}
}
mutex_unlock(&ep->mtx);
return error;
}
/**
* ep_loop_check - Performs a check to verify that adding an epoll file (@file)
* another epoll file (represented by @ep) does not create
* closed loops or too deep chains.
*
* @ep: Pointer to the epoll private data structure.
* @file: Pointer to the epoll file to be checked.
*
* Returns: Returns zero if adding the epoll @file inside current epoll
* structure @ep does not violate the constraints, or -1 otherwise.
*/
static int ep_loop_check(struct eventpoll *ep, struct file *file)
{
int ret;
struct eventpoll *ep_cur, *ep_next;
ret = ep_call_nested(&poll_loop_ncalls,
ep_loop_check_proc, file, ep, current);
/* clear visited list */
list_for_each_entry_safe(ep_cur, ep_next, &visited_list,
visited_list_link) {
ep_cur->visited = 0;
list_del(&ep_cur->visited_list_link);
}
return ret;
}
static void clear_tfile_check_list(void)
{
struct file *file;
/* first clear the tfile_check_list */
while (!list_empty(&tfile_check_list)) {
file = list_first_entry(&tfile_check_list, struct file,
f_tfile_llink);
list_del_init(&file->f_tfile_llink);
fput(file);
}
INIT_LIST_HEAD(&tfile_check_list);
}
/*
* Open an eventpoll file descriptor.
*/
static int do_epoll_create(int flags)
{
int error, fd;
struct eventpoll *ep = NULL;
struct file *file;
/* Check the EPOLL_* constant for consistency. */
BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
if (flags & ~EPOLL_CLOEXEC)
return -EINVAL;
/*
* Create the internal data structure ("struct eventpoll").
*/
error = ep_alloc(&ep);
if (error < 0)
return error;
/*
* Creates all the items needed to setup an eventpoll file. That is,
* a file structure and a free file descriptor.
*/
fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC));
if (fd < 0) {
error = fd;
goto out_free_ep;
}
file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep,
O_RDWR | (flags & O_CLOEXEC));
if (IS_ERR(file)) {
error = PTR_ERR(file);
goto out_free_fd;
}
ep->file = file;
fd_install(fd, file);
return fd;
out_free_fd:
put_unused_fd(fd);
out_free_ep:
ep_free(ep);
return error;
}
SYSCALL_DEFINE1(epoll_create1, int, flags)
{
return do_epoll_create(flags);
}
SYSCALL_DEFINE1(epoll_create, int, size)
{
if (size <= 0)
return -EINVAL;
return do_epoll_create(0);
}
static inline int epoll_mutex_lock(struct mutex *mutex, int depth,
bool nonblock)
{
if (!nonblock) {
mutex_lock_nested(mutex, depth);
return 0;
}
if (mutex_trylock(mutex))
return 0;
return -EAGAIN;
}
int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
bool nonblock)
{
int error;
int full_check = 0;
struct fd f, tf;
struct eventpoll *ep;
struct epitem *epi;
struct eventpoll *tep = NULL;
error = -EBADF;
f = fdget(epfd);
if (!f.file)
goto error_return;
/* Get the "struct file *" for the target file */
tf = fdget(fd);
if (!tf.file)
goto error_fput;
/* The target file descriptor must support poll */
error = -EPERM;
if (!file_can_poll(tf.file))
goto error_tgt_fput;
/* Check if EPOLLWAKEUP is allowed */
if (ep_op_has_event(op))
ep_take_care_of_epollwakeup(epds);
/*
* We have to check that the file structure underneath the file descriptor
* the user passed to us _is_ an eventpoll file. And also we do not permit
* adding an epoll file descriptor inside itself.
*/
error = -EINVAL;
if (f.file == tf.file || !is_file_epoll(f.file))
goto error_tgt_fput;
/*
* epoll adds to the wakeup queue at EPOLL_CTL_ADD time only,
* so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
* Also, we do not currently supported nested exclusive wakeups.
*/
if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) {
if (op == EPOLL_CTL_MOD)
goto error_tgt_fput;
if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
(epds->events & ~EPOLLEXCLUSIVE_OK_BITS)))
goto error_tgt_fput;
}
/*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
ep = f.file->private_data;
/*
* When we insert an epoll file descriptor, inside another epoll file
* descriptor, there is the change of creating closed loops, which are
* better be handled here, than in more critical paths. While we are
* checking for loops we also determine the list of files reachable
* and hang them on the tfile_check_list, so we can check that we
* haven't created too many possible wakeup paths.
*
* We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
* the epoll file descriptor is attaching directly to a wakeup source,
* unless the epoll file descriptor is nested. The purpose of taking the
* 'epmutex' on add is to prevent complex toplogies such as loops and
* deep wakeup paths from forming in parallel through multiple
* EPOLL_CTL_ADD operations.
*/
error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
if (error)
goto error_tgt_fput;
if (op == EPOLL_CTL_ADD) {
if (!list_empty(&f.file->f_ep_links) ||
is_file_epoll(tf.file)) {
mutex_unlock(&ep->mtx);
error = epoll_mutex_lock(&epmutex, 0, nonblock);
if (error)
goto error_tgt_fput;
full_check = 1;
if (is_file_epoll(tf.file)) {
error = -ELOOP;
if (ep_loop_check(ep, tf.file) != 0)
goto error_tgt_fput;
} else {
get_file(tf.file);
list_add(&tf.file->f_tfile_llink,
&tfile_check_list);
}
error = epoll_mutex_lock(&ep->mtx, 0, nonblock);
if (error)
goto error_tgt_fput;
if (is_file_epoll(tf.file)) {
tep = tf.file->private_data;
error = epoll_mutex_lock(&tep->mtx, 1, nonblock);
if (error) {
mutex_unlock(&ep->mtx);
goto error_tgt_fput;
}
}
}
}
/*
* Try to lookup the file inside our RB tree, Since we grabbed "mtx"
* above, we can be sure to be able to use the item looked up by
* ep_find() till we release the mutex.
*/
epi = ep_find(ep, tf.file, fd);
error = -EINVAL;
switch (op) {
case EPOLL_CTL_ADD:
if (!epi) {
epds->events |= EPOLLERR | EPOLLHUP;
error = ep_insert(ep, epds, tf.file, fd, full_check);
} else
error = -EEXIST;
break;
case EPOLL_CTL_DEL:
if (epi)
error = ep_remove(ep, epi);
else
error = -ENOENT;
break;
case EPOLL_CTL_MOD:
if (epi) {
if (!(epi->event.events & EPOLLEXCLUSIVE)) {
epds->events |= EPOLLERR | EPOLLHUP;
error = ep_modify(ep, epi, epds);
}
} else
error = -ENOENT;
break;
}
if (tep != NULL)
mutex_unlock(&tep->mtx);
mutex_unlock(&ep->mtx);
error_tgt_fput:
if (full_check) {
clear_tfile_check_list();
mutex_unlock(&epmutex);
}
fdput(tf);
error_fput:
fdput(f);
error_return:
return error;
}
/*
* The following function implements the controller interface for
* the eventpoll file that enables the insertion/removal/change of
* file descriptors inside the interest set.
*/
SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
struct epoll_event __user *, event)
{
struct epoll_event epds;
if (ep_op_has_event(op) &&
copy_from_user(&epds, event, sizeof(struct epoll_event)))
return -EFAULT;
return do_epoll_ctl(epfd, op, fd, &epds, false);
}
/*
* Implement the event wait interface for the eventpoll file. It is the kernel
* part of the user space epoll_wait(2).
*/
static int do_epoll_wait(int epfd, struct epoll_event __user *events,
int maxevents, int timeout)
{
int error;
struct fd f;
struct eventpoll *ep;
/* The maximum number of event must be greater than zero */
if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
return -EINVAL;
/* Verify that the area passed by the user is writeable */
if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
return -EFAULT;
/* Get the "struct file *" for the eventpoll file */
f = fdget(epfd);
if (!f.file)
return -EBADF;
/*
* We have to check that the file structure underneath the fd
* the user passed to us _is_ an eventpoll file.
*/
error = -EINVAL;
if (!is_file_epoll(f.file))
goto error_fput;
/*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
ep = f.file->private_data;
/* Time to fish for events ... */
error = ep_poll(ep, events, maxevents, timeout);
error_fput:
fdput(f);
return error;
}
SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout)
{
return do_epoll_wait(epfd, events, maxevents, timeout);
}
/*
* Implement the event wait interface for the eventpoll file. It is the kernel
* part of the user space epoll_pwait(2).
*/
SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout, const sigset_t __user *, sigmask,
size_t, sigsetsize)
{
int error;
/*
* If the caller wants a certain signal mask to be set during the wait,
* we apply it here.
*/
error = set_user_sigmask(sigmask, sigsetsize);
if (error)
return error;
error = do_epoll_wait(epfd, events, maxevents, timeout);
restore_saved_sigmask_unless(error == -EINTR);
return error;
}
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
struct epoll_event __user *, events,
int, maxevents, int, timeout,
const compat_sigset_t __user *, sigmask,
compat_size_t, sigsetsize)
{
long err;
/*
* If the caller wants a certain signal mask to be set during the wait,
* we apply it here.
*/
err = set_compat_user_sigmask(sigmask, sigsetsize);
if (err)
return err;
err = do_epoll_wait(epfd, events, maxevents, timeout);
restore_saved_sigmask_unless(err == -EINTR);
return err;
}
#endif
static int __init eventpoll_init(void)
{
struct sysinfo si;
si_meminfo(&si);
/*
* Allows top 4% of lomem to be allocated for epoll watches (per user).
*/
max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) /
EP_ITEM_COST;
BUG_ON(max_user_watches < 0);
/*
* Initialize the structure used to perform epoll file descriptor
* inclusion loops checks.
*/
ep_nested_calls_init(&poll_loop_ncalls);
/*
* We can have many thousands of epitems, so prevent this from
* using an extra cache line on 64-bit (and smaller) CPUs
*/
BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128);
/* Allocates slab cache used to allocate "struct epitem" items */
epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
/* Allocates slab cache used to allocate "struct eppoll_entry" */
pwq_cache = kmem_cache_create("eventpoll_pwq",
sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL);
return 0;
}
fs_initcall(eventpoll_init);
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