diff options
| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2008-02-04 22:27:20 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-05 09:44:07 -0800 |
| commit | 0ccf831cbee94df9c5006dd46248c0f07847dd7c (patch) | |
| tree | 4de8d53c51dc4aff80f35a95cdd185229f0df79e | |
| parent | 96cf49a2c13e8dcf442abaadf6645f6a1fb3ae92 (diff) | |
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 <a.p.zijlstra@chello.nl>
Tested-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/eventpoll.c | 2 | ||||
| -rw-r--r-- | include/linux/wait.h | 16 |
2 files changed, 17 insertions, 1 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 81c04abfb1a..a415f42d32c 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 1f4fb0a81ec..33a2aa9e02f 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); \ |