Hi,
On Wed, Oct 9, 2019 at 5:21 PM Roman Penyaev <rpenyaev@xxxxxxx> wrote:
>
> On 2019-10-09 08:05, hev wrote:
> > From: Heiher <r@xxxxxx>
> >
> > Take the case where we have:
> >
> > t0
> > | (ew)
> > e0
> > | (et)
> > e1
> > | (lt)
> > s0
> >
> > t0: thread 0
> > e0: epoll fd 0
> > e1: epoll fd 1
> > s0: socket fd 0
> > ew: epoll_wait
> > et: edge-trigger
> > lt: level-trigger
> >
> > We remove unnecessary wakeups to prevent the nested epoll that working
> > in edge-
> > triggered mode to waking up continuously.
> >
> > Test code:
> > #include <unistd.h>
> > #include <sys/epoll.h>
> > #include <sys/socket.h>
> >
> > int main(int argc, char *argv[])
> > {
> > int sfd[2];
> > int efd[2];
> > struct epoll_event e;
> >
> > if (socketpair(AF_UNIX, SOCK_STREAM, 0, sfd) < 0)
> > goto out;
> >
> > efd[0] = epoll_create(1);
> > if (efd[0] < 0)
> > goto out;
> >
> > efd[1] = epoll_create(1);
> > if (efd[1] < 0)
> > goto out;
> >
> > e.events = EPOLLIN;
> > if (epoll_ctl(efd[1], EPOLL_CTL_ADD, sfd[0], &e) < 0)
> > goto out;
> >
> > e.events = EPOLLIN | EPOLLET;
> > if (epoll_ctl(efd[0], EPOLL_CTL_ADD, efd[1], &e) < 0)
> > goto out;
> >
> > if (write(sfd[1], "w", 1) != 1)
> > goto out;
> >
> > if (epoll_wait(efd[0], &e, 1, 0) != 1)
> > goto out;
> >
> > if (epoll_wait(efd[0], &e, 1, 0) != 0)
> > goto out;
> >
> > close(efd[0]);
> > close(efd[1]);
> > close(sfd[0]);
> > close(sfd[1]);
> >
> > return 0;
> >
> > out:
> > return -1;
> > }
> >
> > More tests:
> > https://github.com/heiher/epoll-wakeup
> >
> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
> > Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> > Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Eric Wong <e@xxxxxxxxx>
> > Cc: Jason Baron <jbaron@xxxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Roman Penyaev <rpenyaev@xxxxxxx>
> > Cc: Sridhar Samudrala <sridhar.samudrala@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> > Signed-off-by: hev <r@xxxxxx>
> > ---
> > fs/eventpoll.c | 16 ----------------
> > 1 file changed, 16 deletions(-)
> >
> > diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> > index c4159bcc05d9..75fccae100b5 100644
> > --- a/fs/eventpoll.c
> > +++ b/fs/eventpoll.c
> > @@ -671,7 +671,6 @@ static __poll_t ep_scan_ready_list(struct eventpoll
> > *ep,
> > void *priv, int depth, bool ep_locked)
> > {
> > __poll_t res;
> > - int pwake = 0;
> > struct epitem *epi, *nepi;
> > LIST_HEAD(txlist);
> >
> > @@ -738,26 +737,11 @@ static __poll_t ep_scan_ready_list(struct
> > eventpoll *ep,
> > */
> > list_splice(&txlist, &ep->rdllist);
> > __pm_relax(ep->ws);
> > -
> > - if (!list_empty(&ep->rdllist)) {
> > - /*
> > - * Wake up (if active) both the eventpoll wait list and
> > - * the ->poll() wait list (delayed after we release the lock).
> > - */
> > - if (waitqueue_active(&ep->wq))
> > - wake_up(&ep->wq);
> > - if (waitqueue_active(&ep->poll_wait))
> > - pwake++;
> > - }
> > write_unlock_irq(&ep->lock);
> >
> > if (!ep_locked)
> > mutex_unlock(&ep->mtx);
> >
> > - /* We have to call this outside the lock */
> > - if (pwake)
> > - ep_poll_safewake(&ep->poll_wait);
> > -
> > return res;
> > }
>
> This looks good to me. Heiher, mind to make kselftest out of your test
> suite?
>
> Reviewed-by: Roman Penyaev <rpenyaev@xxxxxxx>
>
> --
> Roman
>
>
>
Need to back port this patch to stable branches?
--
Best regards!
Hev
https://hev.cc
