Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=0ccf831cbee94df9c5006dd46248c0f07847dd7c
Commit: 0ccf831cbee94df9c5006dd46248c0f07847dd7c
Parent: 96cf49a2c13e8dcf442abaadf6645f6a1fb3ae92
Author: Peter Zijlstra <[EMAIL PROTECTED]>
AuthorDate: Mon Feb 4 22:27:20 2008 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Tue Feb 5 09:44:07 2008 -0800
lockdep: annotate epoll
On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote:
> I remember I talked with Arjan about this time ago. Basically, since 1)
> you can drop an epoll fd inside another epoll fd 2) callback-based wakeups
> are used, you can see a wake_up() from inside another wake_up(), but they
> will never refer to the same lock instance.
> Think about:
>
> 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. Never hit the same queue, to avoid loops like:
>
> epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
> epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...);
> epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...);
> epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...);
>
> The code "if (tncur->wq == wq || ..." prevents re-entering the same
> queue/lock.
Since the epoll code is very careful to not nest same instance locks
allow the recursion.
Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
Tested-by: Stefan Richter <[EMAIL PROTECTED]>
Acked-by: Davide Libenzi <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
fs/eventpoll.c | 2 +-
include/linux/wait.h | 16 ++++++++++++++++
2 files changed, 17 insertions(+), 1 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 81c04ab..a415f42 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -353,7 +353,7 @@ static void ep_poll_safewake(struct poll_safewake *psw,
wait_queue_head_t *wq)
spin_unlock_irqrestore(&psw->lock, flags);
/* Do really wake up now */
- wake_up(wq);
+ wake_up_nested(wq, 1 + wake_nests);
/* Remove the current task from the list */
spin_lock_irqsave(&psw->lock, flags);
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 1f4fb0a..33a2aa9 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -162,6 +162,22 @@ wait_queue_head_t *FASTCALL(bit_waitqueue(void *, int));
#define wake_up_interruptible_all(x) __wake_up(x, TASK_INTERRUPTIBLE, 0,
NULL)
#define wake_up_interruptible_sync(x) __wake_up_sync((x), TASK_INTERRUPTIBLE,
1)
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/*
+ * macro to avoid include hell
+ */
+#define wake_up_nested(x, s) \
+do { \
+ unsigned long flags; \
+ \
+ spin_lock_irqsave_nested(&(x)->lock, flags, (s)); \
+ wake_up_locked(x); \
+ spin_unlock_irqrestore(&(x)->lock, flags); \
+} while (0)
+#else
+#define wake_up_nested(x, s) wake_up(x)
+#endif
+
#define __wait_event(wq, condition) \
do { \
DEFINE_WAIT(__wait); \
-
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