[PATCH v3 03/13] epoll: allocate user header and user events ring for polling from userspace

Roman Penyaev
2019-05-16T08:58:44Z

This one allocates user header and user events ring according to max items
number, passed as a parameter. User events (index) ring is in a pow2.
Pages, which will be shared between kernel and userspace, are accounted
through user->locked_vm counter.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f598442512f3..e3f82ff0b26b 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -231,6 +231,27 @@ struct eventpoll {

struct file *file;

+ /* User header with array of items */
+ struct epoll_uheader *user_header;
+
+ /* User index, which acts as a ring of coming events */
+ unsigned int *user_index;
+
+ /* Actual length of user header, always aligned on page */
+ unsigned int header_length;
+
+ /* Actual length of user index, always pow2 */
+ unsigned int index_length;
+
+ /* Maximum possible event items */
+ unsigned int max_items_nr;
+
+ /* Items bitmap, is used to get a free bit for new registered epi */
+ unsigned long *items_bm;
+
+ /* Length of both items bitmaps, always aligned on page */
+ unsigned int items_bm_length;
+
/* used to optimize loop detection check */
int visited;
struct list_head visited_list_link;
@@ -381,6 +402,27 @@ static void ep_nested_calls_init(struct nested_calls *ncalls)
spin_lock_init(&ncalls->lock);
}

+static inline unsigned int ep_to_items_length(unsigned int nr)
+{
+ struct epoll_uheader *user_header;
+
+ return PAGE_ALIGN(struct_size(user_header, items, nr));
+}
+
+static inline unsigned int ep_to_index_length(unsigned int nr)
+{
+ struct eventpoll *ep;
+ unsigned int size;
+
+ size = roundup_pow_of_two(nr << ilog2(sizeof(*ep->user_index)));
+ return max_t(typeof(size), size, PAGE_SIZE);
+}
+
+static inline unsigned int ep_to_items_bm_length(unsigned int nr)
+{
+ return PAGE_ALIGN(ALIGN(nr, 8) >> 3);
+}
+
/**
* ep_events_available - Checks if ready events might be available.
*
@@ -836,6 +878,38 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
return 0;
}

+static int ep_account_mem(struct eventpoll *ep, struct user_struct *user)
+{
+ unsigned long nr_pages, page_limit, cur_pages, new_pages;
+
+ nr_pages = ep->header_length >> PAGE_SHIFT;
+ nr_pages += ep->index_length >> PAGE_SHIFT;
+
+ /* Don't allow more pages than we can safely lock */
+ page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+ do {
+ cur_pages = atomic_long_read(&user->locked_vm);
+ new_pages = cur_pages + nr_pages;
+ if (new_pages > page_limit && !capable(CAP_IPC_LOCK))
+ return -ENOMEM;
+ } while (atomic_long_cmpxchg(&user->locked_vm, cur_pages,
+ new_pages) != cur_pages);
+
+ return 0;
+}
+
+static void ep_unaccount_mem(struct eventpoll *ep, struct user_struct *user)
+{
+ unsigned long nr_pages;
+
+ nr_pages = ep->header_length >> PAGE_SHIFT;
+ nr_pages += ep->index_length >> PAGE_SHIFT;
+ if (nr_pages)
+ /* When polled by user */
+ atomic_long_sub(nr_pages, &user->locked_vm);
+}
+
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
@@ -883,8 +957,12 @@ static void ep_free(struct eventpoll *ep)

mutex_unlock(&epmutex);
mutex_destroy(&ep->mtx);
- free_uid(ep->user);
wakeup_source_unregister(ep->ws);
+ vfree(ep->user_header);
+ vfree(ep->user_index);
+ vfree(ep->items_bm);
+ ep_unaccount_mem(ep, ep->user);
+ free_uid(ep->user);
kfree(ep);
}

@@ -1037,7 +1115,7 @@ void eventpoll_release_file(struct file *file)
mutex_unlock(&epmutex);
}

-static int ep_alloc(struct eventpoll **pep)
+static int ep_alloc(struct eventpoll **pep, int flags, size_t max_items)
{
int error;
struct user_struct *user;
@@ -1049,6 +1127,38 @@ static int ep_alloc(struct eventpoll **pep)
if (unlikely(!ep))
goto free_uid;

+ if (flags & EPOLL_USERPOLL) {
+ BUILD_BUG_ON(sizeof(*ep->user_header) !=
+ EPOLL_USERPOLL_HEADER_SIZE);
+ BUILD_BUG_ON(sizeof(ep->user_header->items[0]) != 16);
+
+ if (!max_items || max_items > EP_USERPOLL_MAX_ITEMS_NR) {
+ error = -EINVAL;
+ goto free_ep;
+ }
+ ep->max_items_nr = max_items;
+ ep->header_length = ep_to_items_length(max_items);
+ ep->index_length = ep_to_index_length(max_items);
+ ep->items_bm_length = ep_to_items_bm_length(max_items);
+
+ error = ep_account_mem(ep, user);
+ if (error)
+ goto free_ep;
+
+ ep->user_header = vmalloc_user(ep->header_length);
+ ep->user_index = vmalloc_user(ep->index_length);
+ ep->items_bm = vzalloc(ep->items_bm_length);
+ if (!ep->user_header || !ep->user_index || !ep->items_bm)
+ goto unaccount_mem;
+
+ *ep->user_header = (typeof(*ep->user_header)) {
+ .magic = EPOLL_USERPOLL_HEADER_MAGIC,
+ .header_length = ep->header_length,
+ .index_length = ep->index_length,
+ .max_items_nr = ep->max_items_nr,
+ };
+ }
+
mutex_init(&ep->mtx);
rwlock_init(&ep->lock);
init_waitqueue_head(&ep->wq);
@@ -1062,6 +1172,13 @@ static int ep_alloc(struct eventpoll **pep)

return 0;

+unaccount_mem:
+ ep_unaccount_mem(ep, user);
+free_ep:
+ vfree(ep->user_header);
+ vfree(ep->user_index);
+ vfree(ep->items_bm);
+ kfree(ep);
free_uid:
free_uid(user);
return error;
@@ -2066,7 +2183,7 @@ static void clear_tfile_check_list(void)
/*
* Open an eventpoll file descriptor.
*/
-static int do_epoll_create(int flags)
+static int do_epoll_create(int flags, size_t size)
{
int error, fd;
struct eventpoll *ep = NULL;
@@ -2075,12 +2192,12 @@ static int do_epoll_create(int flags)
/* Check the EPOLL_* constant for consistency. */
BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);

- if (flags & ~EPOLL_CLOEXEC)
+ if (flags & ~(EPOLL_CLOEXEC | EPOLL_USERPOLL))
return -EINVAL;
/*
* Create the internal data structure ("struct eventpoll").
*/
- error = ep_alloc(&ep);
+ error = ep_alloc(&ep, flags, size);
if (error < 0)
return error;
/*
@@ -2111,7 +2228,7 @@ static int do_epoll_create(int flags)

SYSCALL_DEFINE1(epoll_create1, int, flags)
{
- return do_epoll_create(flags);
+ return do_epoll_create(flags, 0);
}

SYSCALL_DEFINE1(epoll_create, int, size)
@@ -2119,7 +2236,7 @@ SYSCALL_DEFINE1(epoll_create, int, size)
if (size <= 0)
return -EINVAL;

- return do_epoll_create(0);
+ return do_epoll_create(0, 0);
}

/*
diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
index 161dfcbcf3b5..95ac0b564529 100644
--- a/include/uapi/linux/eventpoll.h
+++ b/include/uapi/linux/eventpoll.h
@@ -20,7 +20,8 @@
#include <linux/types.h>

/* Flags for epoll_create1. */
-#define EPOLL_CLOEXEC O_CLOEXEC
+#define EPOLL_CLOEXEC O_CLOEXEC
+#define EPOLL_USERPOLL 1

/* Valid opcodes to issue to sys_epoll_ctl() */
#define EPOLL_CTL_ADD 1
--
2.21.0