linux-kernel - [RFC PATCH v2 09/13] epoll: support polling from userspace for ep

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Date:   Mon, 21 Jan 2019 21:14:52 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Roman Penyaev <rpenyaev@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        Jason Baron <jbaron@...mai.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 09/13] epoll: support polling from userspace for ep_remove()

On ep_remove() simply mark a user item with EPOLLREMOVE if the item was
ready (i.e. has some bits set).  That will prevent further user index
entry creation on item ->bit reuse.

Signed-off-by: Roman Penyaev <rpenyaev@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Davidlohr Bueso <dbueso@...e.de>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 fs/eventpoll.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 628a2cadfad6..b9f51f4b94e7 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1025,10 +1025,14 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 
 	rb_erase_cached(&epi->rbn, &ep->rbr);
 
-	write_lock_irq(&ep->lock);
-	if (ep_is_linked(epi))
-		list_del_init(&epi->rdllink);
-	write_unlock_irq(&ep->lock);
+	if (ep_polled_by_user(ep)) {
+		ep_remove_user_item(epi);
+	} else {
+		write_lock_irq(&ep->lock);
+		if (ep_is_linked(epi))
+			list_del_init(&epi->rdllink);
+		write_unlock_irq(&ep->lock);
+	}
 
 	wakeup_source_unregister(ep_wakeup_source(epi));
 	/*
-- 
2.19.1