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epoll: support for disabling items, and a self-test app

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Enhanced epoll_ctl to support EPOLL_CTL_DISABLE, which disables an epoll
item.  If epoll_ctl doesn't return -EBUSY in this case, it is then safe to
delete the epoll item in a multi-threaded environment.  Also added a new
test_epoll self- test app to both demonstrate the need for this feature
and test it.

Signed-off-by: Paton J. Lewis <palewis@adobe.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Paul Holland <pholland@adobe.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paton J. Lewis
2012-10-04 17:13:39 -07:00
committed by Linus Torvalds
parent a0a0a7a94c
commit 03a7beb55b
5 changed files with 392 additions and 4 deletions
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38
fs/eventpoll.c
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@@ -346,7 +346,7 @@ static inline struct epitem *ep_item_from_epqueue(poll_table *p)
/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{
return op != EPOLL_CTL_DEL;
return op == EPOLL_CTL_ADD || op == EPOLL_CTL_MOD;
}
/* Initialize the poll safe wake up structure */
@@ -676,6 +676,34 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
return 0;
}
/*
* Disables a "struct epitem" in the eventpoll set. Returns -EBUSY if the item
* had no event flags set, indicating that another thread may be currently
* handling that item's events (in the case that EPOLLONESHOT was being
* used). Otherwise a zero result indicates that the item has been disabled
* from receiving events. A disabled item may be re-enabled via
* EPOLL_CTL_MOD. Must be called with "mtx" held.
*/
static int ep_disable(struct eventpoll *ep, struct epitem *epi)
{
int result = 0;
unsigned long flags;
spin_lock_irqsave(&ep->lock, flags);
if (epi->event.events & ~EP_PRIVATE_BITS) {
if (ep_is_linked(&epi->rdllink))
list_del_init(&epi->rdllink);
/* Ensure ep_poll_callback will not add epi back onto ready
list: */
epi->event.events &= EP_PRIVATE_BITS;
}
else
result = -EBUSY;
spin_unlock_irqrestore(&ep->lock, flags);
return result;
}
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
@@ -1020,8 +1048,6 @@ static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
rb_insert_color(&epi->rbn, &ep->rbr);
}
#define PATH_ARR_SIZE 5
/*
* These are the number paths of length 1 to 5, that we are allowing to emanate
@@ -1787,6 +1813,12 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
} else
error = -ENOENT;
break;
case EPOLL_CTL_DISABLE:
if (epi)
error = ep_disable(ep, epi);
else
error = -ENOENT;
break;
}
mutex_unlock(&ep->mtx);