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Message-ID: <send-serie.davidel@xmailserver.org.4556.1179084280.1>
Date: Sun, 13 May 2007 12:24:40 -0700
From: Davide Libenzi <davidel@...ilserver.org>
To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Subject: [patch 1/1] epoll fix some comments ...
Fixes some epoll code comments. Andrew, this goes on top of the two
patches I posted on Friday.
Signed-off-by: Davide Libenzi <davidel@...ilserver.org>
- Davide
Index: linux-2.6.21-git17.epmod/fs/eventpoll.c
===================================================================
--- linux-2.6.21-git17.epmod.orig/fs/eventpoll.c 2007-05-12 12:50:22.000000000 -0700
+++ linux-2.6.21-git17.epmod/fs/eventpoll.c 2007-05-13 12:13:53.000000000 -0700
@@ -134,7 +134,7 @@
* have an entry of this type linked to the "rbr" RB tree.
*/
struct epitem {
- /* RB-Tree node used to link this structure to the eventpoll rb-tree */
+ /* RB tree node used to link this structure to the eventpoll RB tree */
struct rb_node rbn;
/* List header used to link this structure to the eventpoll ready list */
@@ -191,7 +191,7 @@
/* List of ready file descriptors */
struct list_head rdllist;
- /* RB-Tree root used to store monitored fd structs */
+ /* RB tree root used to store monitored fd structs */
struct rb_root rbr;
/*
@@ -241,7 +241,7 @@
static struct kmem_cache *pwq_cache __read_mostly;
-/* Setup the structure that is used as key for the rb-tree */
+/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,
struct file *file, int fd)
{
@@ -249,7 +249,7 @@
ffd->fd = fd;
}
-/* Compare rb-tree keys */
+/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,
struct epoll_filefd *p2)
{
@@ -257,20 +257,20 @@
(p1->file < p2->file ? -1 : p1->fd - p2->fd));
}
-/* Special initialization for the rb-tree node to detect linkage */
+/* Special initialization for the RB tree node to detect linkage */
static inline void ep_rb_initnode(struct rb_node *n)
{
rb_set_parent(n, n);
}
-/* Removes a node from the rb-tree and marks it for a fast is-linked check */
+/* Removes a node from the RB tree and marks it for a fast is-linked check */
static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r)
{
rb_erase(n, r);
rb_set_parent(n, n);
}
-/* Fast check to verify that the item is linked to the main rb-tree */
+/* Fast check to verify that the item is linked to the main RB tree */
static inline int ep_rb_linked(struct rb_node *n)
{
return rb_parent(n) != n;
@@ -531,6 +531,8 @@
* We don't want to get "file->f_ep_lock" because it is not
* necessary. It is not necessary because we're in the "struct file"
* cleanup path, and this means that noone is using this file anymore.
+ * So, for example, epoll_ctl() cannot hit here sicne if we reach this
+ * point, the file counter already went to zero and fget() would fail.
* The only hit might come from ep_free() but by holding the mutex
* will correctly serialize the operation. We do need to acquire
* "ep->mtx" after "epmutex" because ep_remove() requires it when called
@@ -802,7 +804,9 @@
/*
* We need to do this because an event could have been arrived on some
- * allocated wait queue.
+ * allocated wait queue. Note that we don't care about the ep->ovflist
+ * list, since that is used/cleaned only inside a section bound by "mtx".
+ * And ep_insert() is called with "mtx" held.
*/
spin_lock_irqsave(&ep->lock, flags);
if (ep_is_linked(&epi->rdllink))
@@ -845,8 +849,7 @@
/*
* If the item is "hot" and it is not registered inside the ready
- * list, push it inside. If the item is not "hot" and it is currently
- * registered inside the ready list, unlink it.
+ * list, push it inside.
*/
if (revents & event->events) {
if (!ep_is_linked(&epi->rdllink)) {
@@ -966,15 +969,16 @@
ep->ovflist = EP_UNACTIVE_PTR;
/*
- * In case of error in the event-send loop, we might still have items
- * inside the "txlist". We need to splice them back inside ep->rdllist.
+ * In case of error in the event-send loop, or in case the number of
+ * ready events exceeds the userspace limit, we need to splice the
+ * "txlist" back inside ep->rdllist.
*/
list_splice(&txlist, &ep->rdllist);
if (!list_empty(&ep->rdllist)) {
/*
* Wake up (if active) both the eventpoll wait list and the ->poll()
- * wait list.
+ * wait list (delayed after we release the lock).
*/
if (waitqueue_active(&ep->wq))
__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
@@ -1064,11 +1068,10 @@
}
/*
- * It opens an eventpoll file descriptor by suggesting a storage of "size"
- * file descriptors. The size parameter is just an hint about how to size
- * data structures. It won't prevent the user to store more than "size"
- * file descriptors inside the epoll interface. It is the kernel part of
- * the userspace epoll_create(2).
+ * It opens an eventpoll file descriptor. The "size" parameter is there
+ * for historical reasons, when epoll was using an hash instead of an
+ * RB tree. With the current implementation, the "size" parameter is ignored
+ * (besides sanity checks).
*/
asmlinkage long sys_epoll_create(int size)
{
@@ -1114,8 +1117,7 @@
/*
* The following function implements the controller interface for
* the eventpoll file that enables the insertion/removal/change of
- * file descriptors inside the interest set. It represents
- * the kernel part of the user space epoll_ctl(2).
+ * file descriptors inside the interest set.
*/
asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
struct epoll_event __user *event)
@@ -1167,7 +1169,11 @@
mutex_lock(&ep->mtx);
- /* Try to lookup the file inside our RB tree */
+ /*
+ * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
+ * above, we can be sure to be able to use the item looked up by
+ * ep_find() till we release the mutex.
+ */
epi = ep_find(ep, tfile, fd);
error = -EINVAL;
-
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