From d01f0594d727d2346e4b6ac26ae63e416b60c3f0 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sat, 22 Aug 2020 22:19:12 -0400 Subject: [PATCH] untangling ep_call_nested(): it's all serialized on epmutex. IOW, * no locking is needed to protect the list * the list is actually a stack * no need to check ->ctx * it can bloody well be a static 5-element array - nobody is going to be accessing it in parallel. Signed-off-by: Al Viro --- fs/eventpoll.c | 80 +++++++------------------------------------------- 1 file changed, 11 insertions(+), 69 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index ef73d71a5dc8..43aecae0935c 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -109,25 +109,6 @@ struct epoll_filefd { int fd; } __packed; -/* - * Structure used to track possible nested calls, for too deep recursions - * and loop cycles. - */ -struct nested_call_node { - struct list_head llink; - void *cookie; - void *ctx; -}; - -/* - * This structure is used as collector for nested calls, to check for - * maximum recursion dept and loop cycles. - */ -struct nested_calls { - struct list_head tasks_call_list; - spinlock_t lock; -}; - /* Wait structure used by the poll hooks */ struct eppoll_entry { /* List header used to link this structure to the "struct epitem" */ @@ -273,7 +254,8 @@ static DEFINE_MUTEX(epmutex); static u64 loop_check_gen = 0; /* Used to check for epoll file descriptor inclusion loops */ -static struct nested_calls poll_loop_ncalls; +static void *cookies[EP_MAX_NESTS + 1]; +static int nesting; /* Slab cache used to allocate "struct epitem" */ static struct kmem_cache *epi_cache __read_mostly; @@ -348,13 +330,6 @@ static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p) return container_of(p, struct eppoll_entry, wait)->base; } -/* Initialize the poll safe wake up structure */ -static void ep_nested_calls_init(struct nested_calls *ncalls) -{ - INIT_LIST_HEAD(&ncalls->tasks_call_list); - spin_lock_init(&ncalls->lock); -} - /** * ep_events_available - Checks if ready events might be available. * @@ -465,47 +440,20 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi) static int ep_call_nested(int (*nproc)(void *, void *, int), void *priv, void *cookie) { - int error, call_nests = 0; - unsigned long flags; - struct nested_calls *ncalls = &poll_loop_ncalls; - struct list_head *lsthead = &ncalls->tasks_call_list; - struct nested_call_node *tncur; - struct nested_call_node tnode; + int error, i; - spin_lock_irqsave(&ncalls->lock, flags); + if (nesting > EP_MAX_NESTS) /* too deep nesting */ + return -1; - /* - * Try to see if the current task is already inside this wakeup call. - * We use a list here, since the population inside this set is always - * very much limited. - */ - list_for_each_entry(tncur, lsthead, llink) { - if (tncur->ctx == current && - (tncur->cookie == cookie || ++call_nests > EP_MAX_NESTS)) { - /* - * Ops ... loop detected or maximum nest level reached. - * We abort this wake by breaking the cycle itself. - */ - error = -1; - goto out_unlock; - } + for (i = 0; i < nesting; i++) { + if (cookies[i] == cookie) /* loop detected */ + return -1; } - - /* Add the current task and cookie to the list */ - tnode.ctx = current; - tnode.cookie = cookie; - list_add(&tnode.llink, lsthead); - - spin_unlock_irqrestore(&ncalls->lock, flags); + cookies[nesting++] = cookie; /* Call the nested function */ - error = (*nproc)(priv, cookie, call_nests); - - /* Remove the current task from the list */ - spin_lock_irqsave(&ncalls->lock, flags); - list_del(&tnode.llink); -out_unlock: - spin_unlock_irqrestore(&ncalls->lock, flags); + error = (*nproc)(priv, cookie, nesting - 1); + nesting--; return error; } @@ -2379,12 +2327,6 @@ static int __init eventpoll_init(void) EP_ITEM_COST; BUG_ON(max_user_watches < 0); - /* - * Initialize the structure used to perform epoll file descriptor - * inclusion loops checks. - */ - ep_nested_calls_init(&poll_loop_ncalls); - /* * We can have many thousands of epitems, so prevent this from * using an extra cache line on 64-bit (and smaller) CPUs -- 2.20.1