* Christoph Hellwig <hch@xxxxxx> wrote:
> The eoll code currently always uses the unlocked waitqueue helpers for
s/eoll
/epoll
> ep->wq, but instead of holding the lock inside the waitqueue around these
> calls, as expected by the epoll code uses its own lock.
Hm, that reads a bit weirdly. How about:
The epoll code currently uses the unlocked waitqueue helpers for managing
ep->wq, but instead of holding the waitqueue lock around these calls, it
uses its own ep->lock spinlock.
> Given that the
> waitqueue is not exposed to the rest of the kernel this actually works
> ok at the moment, but prevents the epoll locking rules from being
> enforced using lockdep. Remove ep->lock and use the waitqueue lock
> to not only reduce the size of struct eventpoll but also make sure we
> can assert locking invariations in the waitqueue code.
s/but also make sure
but also to make sure
s/invariations
/invariants
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/eventpoll.c | 46 ++++++++++++++++++++++------------------------
> 1 file changed, 22 insertions(+), 24 deletions(-)
>
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index afd548ebc328..2b2c5ac80e26 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -182,11 +182,10 @@ struct epitem {
> * This structure is stored inside the "private_data" member of the file
> * structure and represents the main data structure for the eventpoll
> * interface.
> + *
> + * Access to it is protected by the lock inside wq.
> */
> struct eventpoll {
> - /* Protect the access to this structure */
> - spinlock_t lock;
> -
> /*
> * This mutex is used to ensure that files are not removed
> * while epoll is using them. This is held during the event
> @@ -210,7 +209,7 @@ struct eventpoll {
> /*
> * This is a single linked list that chains all the "struct epitem" that
> * happened while transferring ready events to userspace w/out
> - * holding ->lock.
> + * holding ->wq.lock.
> */
Neat trick!
This exposes some waitqueue internals, but AFAICS the FUSE code already does a
similar trick with fiq->waitq.lock so there's precedent.
Peter, what do you think?
Thanks,
Ingo
