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sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming

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So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.

Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.

To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:

	struct wait_queue_head::task_list	=> ::head
	struct wait_queue_entry::task_list	=> ::entry

For example, this code:

	rqw->wait.task_list.next != &wait->task_list

... is was pretty unclear (to me) what it's doing, while now it's written this way:

	rqw->wait.head.next != &wait->entry

... which makes it pretty clear that we are iterating a list until we see the head.

Other examples are:

	list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
	list_for_each_entry(wq, &fence->wait.task_list, task_list) {

... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:

	list_for_each_entry_safe(pos, next, &x->head, entry) {
	list_for_each_entry(wq, &fence->wait.head, entry) {

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar
2017-06-20 12:06:46 +02:00
parent 5822a454d6
commit 2055da9738
18 changed files with 66 additions and 68 deletions
Download Patch File Download Diff File Expand all files Collapse all files
fs/userfaultfd.c
+11 -11
View File
@@ -129,7 +129,7 @@ static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
* wouldn't be enough, the smp_mb__before_spinlock is
* enough to avoid an explicit smp_mb() here.
*/
list_del_init(&wq->task_list);
list_del_init(&wq->entry);
out:
return ret;
}
@@ -522,13 +522,13 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
* and it's fine not to block on the spinlock. The uwq on this
* kernel stack can be released after the list_del_init.
*/
if (!list_empty_careful(&uwq.wq.task_list)) {
if (!list_empty_careful(&uwq.wq.entry)) {
spin_lock(&ctx->fault_pending_wqh.lock);
/*
* No need of list_del_init(), the uwq on the stack
* will be freed shortly anyway.
*/
list_del(&uwq.wq.task_list);
list_del(&uwq.wq.entry);
spin_unlock(&ctx->fault_pending_wqh.lock);
}
@@ -869,7 +869,7 @@ static inline struct userfaultfd_wait_queue *find_userfault_in(
if (!waitqueue_active(wqh))
goto out;
/* walk in reverse to provide FIFO behavior to read userfaults */
wq = list_last_entry(&wqh->task_list, typeof(*wq), task_list);
wq = list_last_entry(&wqh->head, typeof(*wq), entry);
uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
out:
return uwq;
@@ -1003,14 +1003,14 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
* changes __remove_wait_queue() to use
* list_del_init() in turn breaking the
* !list_empty_careful() check in
* handle_userfault(). The uwq->wq.task_list
* handle_userfault(). The uwq->wq.head list
* must never be empty at any time during the
* refile, or the waitqueue could disappear
* from under us. The "wait_queue_head_t"
* parameter of __remove_wait_queue() is unused
* anyway.
*/
list_del(&uwq->wq.task_list);
list_del(&uwq->wq.entry);
__add_wait_queue(&ctx->fault_wqh, &uwq->wq);
write_seqcount_end(&ctx->refile_seq);
@@ -1032,7 +1032,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
fork_nctx = (struct userfaultfd_ctx *)
(unsigned long)
uwq->msg.arg.reserved.reserved1;
list_move(&uwq->wq.task_list, &fork_event);
list_move(&uwq->wq.entry, &fork_event);
spin_unlock(&ctx->event_wqh.lock);
ret = 0;
break;
@@ -1069,8 +1069,8 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
if (!list_empty(&fork_event)) {
uwq = list_first_entry(&fork_event,
typeof(*uwq),
wq.task_list);
list_del(&uwq->wq.task_list);
wq.entry);
list_del(&uwq->wq.entry);
__add_wait_queue(&ctx->event_wqh, &uwq->wq);
userfaultfd_event_complete(ctx, uwq);
}
@@ -1752,12 +1752,12 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
unsigned long pending = 0, total = 0;
spin_lock(&ctx->fault_pending_wqh.lock);
list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) {
list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
pending++;
total++;
}
list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) {
list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
total++;
}