Starting with commit 7cffb5f6 (MDEV-23399)
the function buf_flush_page() will first acquire block->lock and only
after that invoke set_io_fix(). Before that, it was possible to reach
a livelock between buf_page_create() and buf_flush_page().

buf_page_create(): Directly try acquiring the exclusive page latch
without checking whether the page is io-fixed or buffer-fixed.
(As a matter of fact, the have_x_latch() check is not strictly necessary,
because we still support recursive X-latches.)
In case of a latch conflict, wait while allowing buf_page_write_complete()
to acquire buf_pool.mutex and release the block->lock.

An attempt to wait for exclusive block->lock while holding buf_pool.mutex
would lead to a hang in the tests parts.part_supported_sql_func_innodb
and stress.ddl_innodb, due to a deadlock between buf_page_write_complete()
and buf_page_create().

Similarly, in case of an I/O fixed compressed-only
ROW_FORMAT=COMPRESSED page, we will sleep before retrying.

In both cases, we will sleep for 1ms or until a flush batch is completed.