[RFC PATCH 21/27] take the common part of ep_eventpoll_poll() and ep_item_poll() into helper

Al Viro
2020-10-04T02:40:31Z

The only reason why ep_item_poll() can't simply call ep_eventpoll_poll()
(or, better yet, call vfs_poll() in all cases) is that we need to tell
lockdep how deep into the hierarchy of ->mtx we are. So let's add
a variant of ep_eventpoll_poll() that would take depth explicitly
and turn ep_eventpoll_poll() into wrapper for that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/eventpoll.c | 57 +++++++++++++++++++++++++++------------------------------
1 file changed, 27 insertions(+), 30 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 39947b71f7af..a50b48d26c55 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -732,6 +732,27 @@ static int ep_eventpoll_release(struct inode *inode, struct file *file)
static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
int depth);

+static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth)
+{
+ struct eventpoll *ep = file->private_data;
+ LIST_HEAD(txlist);
+ __poll_t res;
+
+ /* Insert inside our poll wait queue */
+ poll_wait(file, &ep->poll_wait, wait);
+
+ /*
+ * Proceed to find out if wanted events are really available inside
+ * the ready list.
+ */
+ mutex_lock_nested(&ep->mtx, depth);
+ ep_start_scan(ep, &txlist);
+ res = ep_read_events_proc(ep, &txlist, depth + 1);
+ ep_done_scan(ep, &txlist);
+ mutex_unlock(&ep->mtx);
+ return res;
+}
+
/*
* Differs from ep_eventpoll_poll() in that internal callers already have
* the ep->mtx so we need to start from depth=1, such that mutex_lock_nested()
@@ -740,22 +761,14 @@ static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head
static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt,
int depth)
{
- struct eventpoll *ep;
- LIST_HEAD(txlist);
+ struct file *file = epi->ffd.file;
__poll_t res;

pt->_key = epi->event.events;
- if (!is_file_epoll(epi->ffd.file))
- return vfs_poll(epi->ffd.file, pt) & epi->event.events;
-
- ep = epi->ffd.file->private_data;
- poll_wait(epi->ffd.file, &ep->poll_wait, pt);
-
- mutex_lock_nested(&ep->mtx, depth);
- ep_start_scan(ep, &txlist);
- res = ep_read_events_proc(ep, &txlist, depth + 1);
- ep_done_scan(ep, &txlist);
- mutex_unlock(&ep->mtx);
+ if (!is_file_epoll(file))
+ res = vfs_poll(file, pt);
+ else
+ res = __ep_eventpoll_poll(file, pt, depth);
return res & epi->event.events;
}

@@ -786,23 +799,7 @@ static __poll_t ep_read_events_proc(struct eventpoll *ep, struct list_head *head

static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait)
{
- struct eventpoll *ep = file->private_data;
- LIST_HEAD(txlist);
- __poll_t res;
-
- /* Insert inside our poll wait queue */
- poll_wait(file, &ep->poll_wait, wait);
-
- /*
- * Proceed to find out if wanted events are really available inside
- * the ready list.
- */
- mutex_lock(&ep->mtx);
- ep_start_scan(ep, &txlist);
- res = ep_read_events_proc(ep, &txlist, 1);
- ep_done_scan(ep, &txlist);
- mutex_unlock(&ep->mtx);
- return res;
+ return __ep_eventpoll_poll(file, wait, 0);
}

#ifdef CONFIG_PROC_FS
--
2.11.0