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authorDavide Libenzi <davidel@xmailserver.org>2006-06-25 05:48:14 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-25 10:01:13 -0700
commit3419b23a919698f75944d3e0d97eb1d9c51e4bb6 (patch)
treee1b4b6aad754c6a40137c0a563d823074501da2d
parent4ad3bcf3146aa12f41262bb5dd1d9f1778e085b1 (diff)
downloadop-kernel-dev-3419b23a919698f75944d3e0d97eb1d9c51e4bb6.zip
op-kernel-dev-3419b23a919698f75944d3e0d97eb1d9c51e4bb6.tar.gz
[PATCH] epoll: use unlocked wqueue operations
A few days ago Arjan signaled a lockdep red flag on epoll locks, and precisely between the epoll's device structure lock (->lock) and the wait queue head lock (->lock). Like I explained in another email, and directly to Arjan, this can't happen in reality because of the explicit check at eventpoll.c:592, that does not allow to drop an epoll fd inside the same epoll fd. Since lockdep is working on per-structure locks, it will never be able to know of policies enforced in other parts of the code. It was decided time ago of having the ability to drop epoll fds inside other epoll fds, that triggers a very trick wakeup operations (due to possibly reentrant callback-driven wakeups) handled by the ep_poll_safewake() function. While looking again at the code though, I noticed that all the operations done on the epoll's main structure wait queue head (->wq) are already protected by the epoll lock (->lock), so that locked-style functions can be used to manipulate the ->wq member. This makes both a lock-acquire save, and lockdep happy. Running totalmess on my dual opteron for a while did not reveal any problem so far: http://www.xmailserver.org/totalmess.c Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--fs/eventpoll.c17
-rw-r--r--include/linux/eventpoll.h2
2 files changed, 11 insertions, 8 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 08e7e6a..9c677bb 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1,6 +1,6 @@
/*
* fs/eventpoll.c ( Efficent event polling implementation )
- * Copyright (C) 2001,...,2003 Davide Libenzi
+ * Copyright (C) 2001,...,2006 Davide Libenzi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@@ -1004,7 +1004,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
- wake_up(&ep->wq);
+ __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
@@ -1083,7 +1083,8 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
/* Notify waiting tasks that events are available */
if (waitqueue_active(&ep->wq))
- wake_up(&ep->wq);
+ __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
+ TASK_INTERRUPTIBLE);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
@@ -1260,7 +1261,8 @@ is_linked:
* wait list.
*/
if (waitqueue_active(&ep->wq))
- wake_up(&ep->wq);
+ __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
+ TASK_INTERRUPTIBLE);
if (waitqueue_active(&ep->poll_wait))
pwake++;
@@ -1444,7 +1446,8 @@ static void ep_reinject_items(struct eventpoll *ep, struct list_head *txlist)
* wait list.
*/
if (waitqueue_active(&ep->wq))
- wake_up(&ep->wq);
+ __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
+ TASK_INTERRUPTIBLE);
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
@@ -1516,7 +1519,7 @@ retry:
* ep_poll_callback() when events will become available.
*/
init_waitqueue_entry(&wait, current);
- add_wait_queue(&ep->wq, &wait);
+ __add_wait_queue(&ep->wq, &wait);
for (;;) {
/*
@@ -1536,7 +1539,7 @@ retry:
jtimeout = schedule_timeout(jtimeout);
write_lock_irqsave(&ep->lock, flags);
}
- remove_wait_queue(&ep->wq, &wait);
+ __remove_wait_queue(&ep->wq, &wait);
set_current_state(TASK_RUNNING);
}
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 1e4bdfc..84cfa8b 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -1,6 +1,6 @@
/*
* include/linux/eventpoll.h ( Efficent event polling implementation )
- * Copyright (C) 2001,...,2003 Davide Libenzi
+ * Copyright (C) 2001,...,2006 Davide Libenzi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
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