io_uring: use constants for cq_overflow bitfield

Prepare to use this bitfield for more flags by using constants instead of
magic value 0
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220421091345.2115755-5-dylany@fb.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -431,7 +431,7 @@ struct io_ring_ctx {
 	struct wait_queue_head	sqo_sq_wait;
 	struct list_head	sqd_list;
 
-	unsigned long		check_cq_overflow;
+	unsigned long		check_cq;
 
 	struct {
 		/*
@@ -903,6 +903,10 @@ struct io_cqe {
 	};
 };
 
+enum {
+	IO_CHECK_CQ_OVERFLOW_BIT,
+};
+
 /*
  * NOTE! Each of the iocb union members has the file pointer
  * as the first entry in their struct definition. So you can
@@ -2024,7 +2028,7 @@ static bool __io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
 
 	all_flushed = list_empty(&ctx->cq_overflow_list);
 	if (all_flushed) {
-		clear_bit(0, &ctx->check_cq_overflow);
+		clear_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
 		WRITE_ONCE(ctx->rings->sq_flags,
 			   ctx->rings->sq_flags & ~IORING_SQ_CQ_OVERFLOW);
 	}
@@ -2040,7 +2044,7 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx)
 {
 	bool ret = true;
 
-	if (test_bit(0, &ctx->check_cq_overflow)) {
+	if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq)) {
 		/* iopoll syncs against uring_lock, not completion_lock */
 		if (ctx->flags & IORING_SETUP_IOPOLL)
 			mutex_lock(&ctx->uring_lock);
@@ -2118,7 +2122,7 @@ static bool io_cqring_event_overflow(struct io_ring_ctx *ctx, u64 user_data,
 		return false;
 	}
 	if (list_empty(&ctx->cq_overflow_list)) {
-		set_bit(0, &ctx->check_cq_overflow);
+		set_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq);
 		WRITE_ONCE(ctx->rings->sq_flags,
 			   ctx->rings->sq_flags | IORING_SQ_CQ_OVERFLOW);
 
@@ -2960,7 +2964,7 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min)
 	 * If we do, we can potentially be spinning for commands that
 	 * already triggered a CQE (eg in error).
 	 */
-	if (test_bit(0, &ctx->check_cq_overflow))
+	if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
 		__io_cqring_overflow_flush(ctx, false);
 	if (io_cqring_events(ctx))
 		return 0;
@@ -8300,7 +8304,8 @@ static int io_wake_function(struct wait_queue_entry *curr, unsigned int mode,
 	 * Cannot safely flush overflowed CQEs from here, ensure we wake up
 	 * the task, and the next invocation will do it.
 	 */
-	if (io_should_wake(iowq) || test_bit(0, &iowq->ctx->check_cq_overflow))
+	if (io_should_wake(iowq) ||
+	    test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &iowq->ctx->check_cq))
 		return autoremove_wake_function(curr, mode, wake_flags, key);
 	return -1;
 }
@@ -8328,7 +8333,7 @@ static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
 	if (ret || io_should_wake(iowq))
 		return ret;
 	/* let the caller flush overflows, retry */
-	if (test_bit(0, &ctx->check_cq_overflow))
+	if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
 		return 1;
 
 	if (!schedule_hrtimeout(&timeout, HRTIMER_MODE_ABS))
@@ -10123,7 +10128,8 @@ static __poll_t io_uring_poll(struct file *file, poll_table *wait)
 	 * Users may get EPOLLIN meanwhile seeing nothing in cqring, this
 	 * pushs them to do the flush.
 	 */
-	if (io_cqring_events(ctx) || test_bit(0, &ctx->check_cq_overflow))
+	if (io_cqring_events(ctx) ||
+	    test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
 		mask |= EPOLLIN | EPOLLRDNORM;
 
 	return mask;